diff --git a/src/Constants.php b/src/Constants.php
index 1a1f2656..7b39c159 100644
--- a/src/Constants.php
+++ b/src/Constants.php
@@ -152,4 +152,7 @@ class Constants extends \SimpleSAML\XML\Constants
     public const XMLENC_ELEMENT = 'http://www.w3.org/2001/04/xmlenc#Element';
     public const XMLENC_ENCRYPTEDKEY = 'http://www.w3.org/2001/04/xmlenc#EncryptedKey';
     public const XMLENC_EXI = 'http://www.w3.org/2009/xmlenc11#EXI';
+
+    // The namespace for the Elliptic Curve Diffie-Hellman Ephemeral Static (ECDH-ES) algorithm
+    public const XMLENC11_ECDH_ES = 'http://www.w3.org/2009/xmlenc11#ECDH-ES';
 }
diff --git a/src/XML/ds/AbstractKeyInfoType.php b/src/XML/ds/AbstractKeyInfoType.php
new file mode 100644
index 00000000..b266045f
--- /dev/null
+++ b/src/XML/ds/AbstractKeyInfoType.php
@@ -0,0 +1,117 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\ds;
+
+use DOMElement;
+use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+use SimpleSAML\XML\ExtendableElementTrait;
+use SimpleSAML\XML\SerializableElementInterface;
+use SimpleSAML\XML\XsNamespace as NS;
+use SimpleSAML\XMLSecurity\Constants as C;
+use SimpleSAML\XMLSecurity\Exception\InvalidArgumentException;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractDsElement;
+
+/**
+ * Abstract class representing the KeyInfoType.
+ *
+ * @package simplesamlphp/xml-security
+ */
+abstract class AbstractKeyInfoType extends AbstractDsElement
+{
+    use ExtendableElementTrait;
+
+    /** @var \SimpleSAML\XML\XsNamespace */
+    public const XS_ANY_ELT_NAMESPACE = NS::OTHER;
+
+
+    /**
+     * Initialize a KeyInfo element.
+     *
+     * @param (
+     *     \SimpleSAML\XMLSecurity\XML\ds\KeyName|
+     *     \SimpleSAML\XMLSecurity\XML\ds\KeyValue|
+     *     \SimpleSAML\XMLSecurity\XML\ds\RetrievalMethod|
+     *     \SimpleSAML\XMLSecurity\XML\ds\X509Data|
+     *     \SimpleSAML\XML\SerializableElementInterface
+     * )[] $info
+     * @param string|null $Id
+     */
+    final public function __construct(
+        protected array $info,
+        protected ?string $Id = null,
+    ) {
+        Assert::notEmpty(
+            $info,
+            sprintf(
+                '%s:%s cannot be empty',
+                static::getNamespacePrefix(),
+                static::getLocalName(),
+            ),
+            InvalidArgumentException::class,
+        );
+        Assert::maxCount($info, C::UNBOUNDED_LIMIT);
+        Assert::allIsInstanceOf(
+            $info,
+            SerializableElementInterface::class,
+            InvalidArgumentException::class,
+        );
+        Assert::nullOrValidNCName($Id);
+
+        foreach ($info as $item) {
+            if ($item instanceof AbstractDsElement) {
+                Assert::isInstanceOfAny(
+                    $item,
+                    [KeyName::class, KeyValue::class, RetrievalMethod::class, X509Data::class],
+                    SchemaViolationException::class,
+                );
+            }
+        }
+    }
+
+
+    /**
+     * Collect the value of the Id-property
+     *
+     * @return string|null
+     */
+    public function getId(): ?string
+    {
+        return $this->Id;
+    }
+
+
+    /**
+     * Collect the value of the info-property
+     *
+     * @return list<\SimpleSAML\XML\SerializableElementInterface>
+     */
+    public function getInfo(): array
+    {
+        return $this->info;
+    }
+
+
+    /**
+     * Convert this KeyInfo to XML.
+     *
+     * @param \DOMElement|null $parent The element we should append this KeyInfo to.
+     * @return \DOMElement
+     */
+    public function toXML(DOMElement $parent = null): DOMElement
+    {
+        $e = $this->instantiateParentElement($parent);
+
+        if ($this->getId() !== null) {
+            $e->setAttribute('Id', $this->getId());
+        }
+
+        foreach ($this->getInfo() as $elt) {
+            $elt->toXML($e);
+        }
+
+        return $e;
+    }
+}
diff --git a/src/XML/ds/KeyInfo.php b/src/XML/ds/KeyInfo.php
index 1c013590..5f499345 100644
--- a/src/XML/ds/KeyInfo.php
+++ b/src/XML/ds/KeyInfo.php
@@ -7,86 +7,16 @@
 use DOMElement;
 use SimpleSAML\Assert\Assert;
 use SimpleSAML\XML\Exception\InvalidDOMElementException;
-use SimpleSAML\XML\Exception\SchemaViolationException;
-use SimpleSAML\XML\ExtendableElementTrait;
-use SimpleSAML\XML\SerializableElementInterface;
-use SimpleSAML\XML\XsNamespace as NS;
-use SimpleSAML\XMLSecurity\Constants as C;
-use SimpleSAML\XMLSecurity\Exception\InvalidArgumentException;
-use SimpleSAML\XMLSecurity\XML\ds\AbstractDsElement;
+
+use function array_merge;
 
 /**
  * Class representing a ds:KeyInfo element.
  *
  * @package simplesamlphp/xml-security
  */
-final class KeyInfo extends AbstractDsElement
+final class KeyInfo extends AbstractKeyInfoType
 {
-    use ExtendableElementTrait;
-
-    /** @var \SimpleSAML\XML\XsNamespace */
-    public const XS_ANY_ELT_NAMESPACE = NS::OTHER;
-
-
-    /**
-     * Initialize a KeyInfo element.
-     *
-     * @param (
-     *     \SimpleSAML\XMLSecurity\XML\ds\KeyName|
-     *     \SimpleSAML\XMLSecurity\XML\ds\KeyValue|
-     *     \SimpleSAML\XMLSecurity\XML\ds\RetrievalMethod|
-     *     \SimpleSAML\XMLSecurity\XML\ds\X509Data|
-     *     \SimpleSAML\XML\SerializableElementInterface
-     * )[] $info
-     * @param string|null $Id
-     */
-    public function __construct(
-        protected array $info,
-        protected ?string $Id = null,
-    ) {
-        Assert::notEmpty($info, 'ds:KeyInfo cannot be empty', InvalidArgumentException::class);
-        Assert::maxCount($info, C::UNBOUNDED_LIMIT);
-        Assert::allIsInstanceOf(
-            $info,
-            SerializableElementInterface::class,
-            InvalidArgumentException::class,
-        );
-        Assert::nullOrValidNCName($Id);
-
-        foreach ($info as $item) {
-            if ($item instanceof AbstractDsElement) {
-                Assert::isInstanceOfAny(
-                    $item,
-                    [KeyName::class, KeyValue::class, RetrievalMethod::class, X509Data::class],
-                    SchemaViolationException::class,
-                );
-            }
-        }
-    }
-
-
-    /**
-     * Collect the value of the Id-property
-     *
-     * @return string|null
-     */
-    public function getId(): ?string
-    {
-        return $this->Id;
-    }
-
-
-    /**
-     * Collect the value of the info-property
-     *
-     * @return list<\SimpleSAML\XML\SerializableElementInterface>
-     */
-    public function getInfo(): array
-    {
-        return $this->info;
-    }
-
-
     /**
      * Convert XML into a KeyInfo
      *
@@ -125,26 +55,4 @@ public static function fromXML(DOMElement $xml): static
 
         return new static($info, $Id);
     }
-
-
-    /**
-     * Convert this KeyInfo to XML.
-     *
-     * @param \DOMElement|null $parent The element we should append this KeyInfo to.
-     * @return \DOMElement
-     */
-    public function toXML(DOMElement $parent = null): DOMElement
-    {
-        $e = $this->instantiateParentElement($parent);
-
-        if ($this->getId() !== null) {
-            $e->setAttribute('Id', $this->getId());
-        }
-
-        foreach ($this->getInfo() as $elt) {
-            $elt->toXML($e);
-        }
-
-        return $e;
-    }
 }
diff --git a/src/XML/element.registry.php b/src/XML/element.registry.php
index 5a371ef8..9a55180d 100644
--- a/src/XML/element.registry.php
+++ b/src/XML/element.registry.php
@@ -43,10 +43,10 @@
         'InclusiveNamespaces' => '\SimpleSAML\XMLSecurity\XML\ec\InclusiveNamespaces',
     ],
     'http://www.w3.org/2001/04/xmlenc#' => [
-//        'AgreementMethod' => '\SimpleSAML\XMLSecurity\XML\xenc\AgreementMethod',
+        'AgreementMethod' => '\SimpleSAML\XMLSecurity\XML\xenc\AgreementMethod',
         'CipherData' => '\SimpleSAML\XMLSecurity\XML\xenc\CipherData',
         'CipherReference' => '\SimpleSAML\XMLSecurity\XML\xenc\CipherReference',
-//        'DHKeyValue' => '\SimpleSAML\XMLSecurity\XML\xenc\DHKeyValue',
+        'DHKeyValue' => '\SimpleSAML\XMLSecurity\XML\xenc\DHKeyValue',
         'EncryptedData' => '\SimpleSAML\XMLSecurity\XML\xenc\EncryptedData',
         'EncryptedKey' => '\SimpleSAML\XMLSecurity\XML\xenc\EncryptedKey',
         'EncryptionProperties' => '\SimpleSAML\XMLSecurity\XML\xenc\EncryptionProperties',
diff --git a/src/XML/xenc/AbstractAgreementMethodType.php b/src/XML/xenc/AbstractAgreementMethodType.php
new file mode 100644
index 00000000..009887d0
--- /dev/null
+++ b/src/XML/xenc/AbstractAgreementMethodType.php
@@ -0,0 +1,159 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use DOMElement;
+use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Exception\InvalidDOMElementException;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+use SimpleSAML\XML\Exception\TooManyElementsException;
+use SimpleSAML\XML\ExtendableElementTrait;
+use SimpleSAML\XML\XsNamespace as NS;
+
+use function array_pop;
+
+/**
+ * A class implementing the xenc:AbstractAgreementMethodType element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+abstract class AbstractAgreementMethodType extends AbstractXencElement
+{
+    use ExtendableElementTrait;
+
+    /** The namespace-attribute for the xs:any element */
+    public const XS_ANY_ELT_NAMESPACE = NS::OTHER;
+
+
+    /**
+     * AgreementMethodType constructor.
+     *
+     * @param string $algorithm
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\KANonce|null $kaNonce
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\OriginatorKeyInfo|null $originatorKeyInfo
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\RecipientKeyInfo|null $recipientKeyInfo
+     * @param list<\SimpleSAML\XML\SerializableElementInterface> $children
+     */
+    final public function __construct(
+        protected string $algorithm,
+        protected ?KANonce $kaNonce = null,
+        protected ?OriginatorKeyInfo $originatorKeyInfo = null,
+        protected ?RecipientKeyInfo $recipientKeyInfo = null,
+        protected array $children = [],
+    ) {
+        Assert::validURI($algorithm, SchemaViolationException::class); // Covers the empty string
+
+        $this->setElements($children);
+    }
+
+
+    /**
+     * Get the URI identifying the algorithm used by this agreement method.
+     *
+     * @return string
+     */
+    public function getAlgorithm(): string
+    {
+        return $this->algorithm;
+    }
+
+
+    /**
+     * Get the KA-Nonce.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\KANonce|null
+     */
+    public function getKANonce(): ?KANonce
+    {
+        return $this->kaNonce;
+    }
+
+
+    /**
+     * Get the Originator KeyInfo.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\OriginatorKeyInfo|null
+     */
+    public function getOriginatorKeyInfo(): ?OriginatorKeyInfo
+    {
+        return $this->originatorKeyInfo;
+    }
+
+
+    /**
+     * Get the Recipient KeyInfo.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\RecipientKeyInfo|null
+     */
+    public function getRecipientKeyInfo(): ?RecipientKeyInfo
+    {
+        return $this->recipientKeyInfo;
+    }
+
+
+    /**
+     * Initialize an AgreementMethod object from an existing XML.
+     *
+     * @param \DOMElement $xml
+     * @return static
+     *
+     * @throws \SimpleSAML\XML\Exception\InvalidDOMElementException
+     *   if the qualified name of the supplied element is wrong
+     * @throws \SimpleSAML\XML\Exception\MissingAttributeException
+     *   if the supplied element is missing one of the mandatory attributes
+     * @throws \SimpleSAML\XML\Exception\TooManyElementsException
+     *   if too many child-elements of a type are specified
+     */
+    public static function fromXML(DOMElement $xml): static
+    {
+        Assert::same($xml->localName, 'AgreementMethod', InvalidDOMElementException::class);
+        Assert::same($xml->namespaceURI, static::NS, InvalidDOMElementException::class);
+
+        $algorithm = self::getAttribute($xml, 'Algorithm');
+
+        $kaNonce = KANonce::getChildrenOfClass($xml);
+        Assert::maxCount($kaNonce, 1, TooManyElementsException::class);
+
+        $originatorKeyInfo = OriginatorKeyInfo::getChildrenOfClass($xml);
+        Assert::maxCount($originatorKeyInfo, 1, TooManyElementsException::class);
+
+        $recipientKeyInfo = RecipientKeyInfo::getChildrenOfClass($xml);
+        Assert::maxCount($recipientKeyInfo, 1, TooManyElementsException::class);
+
+        $children = self::getChildElementsFromXML($xml);
+
+        return new static(
+            $algorithm,
+            array_pop($kaNonce),
+            array_pop($originatorKeyInfo),
+            array_pop($recipientKeyInfo),
+            $children,
+        );
+    }
+
+
+    /**
+     * Convert this AgreementMethod object to XML.
+     *
+     * @param \DOMElement|null $parent The element we should append this AgreementMethod to.
+     * @return \DOMElement
+     */
+    public function toXML(DOMElement $parent = null): DOMElement
+    {
+        $e = $this->instantiateParentElement($parent);
+        $e->setAttribute('Algorithm', $this->getAlgorithm());
+
+        $this->getKANonce()?->toXML($e);
+
+        foreach ($this->getElements() as $child) {
+            $child->toXML($e);
+        }
+
+        $this->getOriginatorKeyInfo()?->toXML($e);
+        $this->getRecipientKeyInfo()?->toXML($e);
+
+        return $e;
+    }
+}
diff --git a/src/XML/xenc/AbstractDHKeyValueType.php b/src/XML/xenc/AbstractDHKeyValueType.php
new file mode 100644
index 00000000..66b60d81
--- /dev/null
+++ b/src/XML/xenc/AbstractDHKeyValueType.php
@@ -0,0 +1,188 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use DOMElement;
+use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Exception\InvalidDOMElementException;
+use SimpleSAML\XML\Exception\MissingElementException;
+use SimpleSAML\XML\Exception\SchemaViolationException;
+use SimpleSAML\XML\Exception\TooManyElementsException;
+
+use function array_pop;
+
+/**
+ * A class implementing the xenc:AbstractDHKeyValueType element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+abstract class AbstractDHKeyValueType extends AbstractXencElement
+{
+    /**
+     * DHKeyValueType constructor.
+     *
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\XencPublic $xencPublic
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\P|null $p
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\Q|null $q
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\Generator|null $generator
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\Seed|null $seed
+     * @param \SimpleSAML\XMLSecurity\XML\xenc\PgenCounter|null $pgenCounter
+     */
+    final public function __construct(
+        protected XencPublic $xencPublic,
+        protected ?P $p = null,
+        protected ?Q $q = null,
+        protected ?Generator $generator = null,
+        protected ?Seed $seed = null,
+        protected ?PgenCounter $pgenCounter = null,
+    ) {
+        if ($p !== null || $q !== null || $generator !== null) {
+            Assert::allNotNull([$p, $q, $generator], SchemaViolationException::class);
+        } else {
+            Assert::allNull([$p, $q, $generator], SchemaViolationException::class);
+        }
+
+        if ($seed !== null || $pgenCounter !== null) {
+            Assert::allNotNull([$seed, $pgenCounter], SchemaViolationException::class);
+        } else {
+            Assert::allNull([$seed, $pgenCounter], SchemaViolationException::class);
+        }
+    }
+
+
+    /**
+     * Get the Public.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\XencPublic
+     */
+    public function getPublic(): XencPublic
+    {
+        return $this->xencPublic;
+    }
+
+
+    /**
+     * Get the P.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\P|null
+     */
+    public function getP(): ?P
+    {
+        return $this->p;
+    }
+
+
+    /**
+     * Get the Q.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\Q|null
+     */
+    public function getQ(): ?Q
+    {
+        return $this->q;
+    }
+
+
+    /**
+     * Get the Generator.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\Generator|null
+     */
+    public function getGenerator(): ?Generator
+    {
+        return $this->generator;
+    }
+
+
+    /**
+     * Get the Seed.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\Seed|null
+     */
+    public function getSeed(): ?Seed
+    {
+        return $this->seed;
+    }
+
+
+    /**
+     * Get the PgenCounter.
+     *
+     * @return \SimpleSAML\XMLSecurity\XML\xenc\PgenCounter|null
+     */
+    public function getPgenCounter(): ?PgenCounter
+    {
+        return $this->pgenCounter;
+    }
+
+
+    /**
+     * Initialize an DHKeyValue object from an existing XML.
+     *
+     * @param \DOMElement $xml
+     * @return static
+     *
+     * @throws \SimpleSAML\XML\Exception\InvalidDOMElementException
+     *   if the qualified name of the supplied element is wrong
+     * @throws \SimpleSAML\XML\Exception\MissingAttributeException
+     *   if the supplied element is missing one of the mandatory attributes
+     * @throws \SimpleSAML\XML\Exception\TooManyElementsException
+     *   if too many child-elements of a type are specified
+     */
+    public static function fromXML(DOMElement $xml): static
+    {
+        Assert::same($xml->localName, 'DHKeyValue', InvalidDOMElementException::class);
+        Assert::same($xml->namespaceURI, static::NS, InvalidDOMElementException::class);
+
+        $xencPublic = XencPublic::getChildrenOfClass($xml);
+        Assert::minCount($xencPublic, 1, MissingElementException::class);
+        Assert::maxCount($xencPublic, 1, TooManyElementsException::class);
+
+        $p = P::getChildrenOfClass($xml);
+        Assert::maxCount($p, 1, TooManyElementsException::class);
+
+        $q = Q::getChildrenOfClass($xml);
+        Assert::maxCount($q, 1, TooManyElementsException::class);
+
+        $generator = Generator::getChildrenOfClass($xml);
+        Assert::maxCount($generator, 1, TooManyElementsException::class);
+
+        $seed = Seed::getChildrenOfClass($xml);
+        Assert::maxCount($seed, 1, TooManyElementsException::class);
+
+        $pgenCounter = PgenCounter::getChildrenOfClass($xml);
+        Assert::maxCount($pgenCounter, 1, TooManyElementsException::class);
+
+        return new static(
+            array_pop($xencPublic),
+            array_pop($p),
+            array_pop($q),
+            array_pop($generator),
+            array_pop($seed),
+            array_pop($pgenCounter),
+        );
+    }
+
+
+    /**
+     * Convert this DHKeyValue object to XML.
+     *
+     * @param \DOMElement|null $parent The element we should append this DHKeyValue to.
+     * @return \DOMElement
+     */
+    public function toXML(DOMElement $parent = null): DOMElement
+    {
+        $e = $this->instantiateParentElement($parent);
+
+        $this->getP()?->toXML($e);
+        $this->getQ()?->toXML($e);
+        $this->getGenerator()?->toXML($e);
+        $this->getPublic()->toXML($e);
+        $this->getSeed()?->toXML($e);
+        $this->getPgenCounter()?->toXML($e);
+
+        return $e;
+    }
+}
diff --git a/src/XML/xenc/AgreementMethod.php b/src/XML/xenc/AgreementMethod.php
new file mode 100644
index 00000000..3a7bc106
--- /dev/null
+++ b/src/XML/xenc/AgreementMethod.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+/**
+ * A class implementing the xenc:AgreementMethod element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+final class AgreementMethod extends AbstractAgreementMethodType
+{
+}
diff --git a/src/XML/xenc/DHKeyValue.php b/src/XML/xenc/DHKeyValue.php
new file mode 100644
index 00000000..66ab7082
--- /dev/null
+++ b/src/XML/xenc/DHKeyValue.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+/**
+ * A class implementing the xenc:DHKeyValue element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+final class DHKeyValue extends AbstractDHKeyValueType
+{
+}
diff --git a/src/XML/xenc/Generator.php b/src/XML/xenc/Generator.php
new file mode 100644
index 00000000..7adba9d2
--- /dev/null
+++ b/src/XML/xenc/Generator.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use SimpleSAML\XML\Base64ElementTrait;
+
+/**
+ * Class representing a xenc:Generator element.
+ *
+ * @package simplesaml/xml-security
+ */
+final class Generator extends AbstractXencElement
+{
+    use Base64ElementTrait;
+
+
+    /**
+     * @param string $content
+     */
+    public function __construct(string $content)
+    {
+        $this->setContent($content);
+    }
+}
diff --git a/src/XML/xenc/KANonce.php b/src/XML/xenc/KANonce.php
new file mode 100644
index 00000000..44e72e2a
--- /dev/null
+++ b/src/XML/xenc/KANonce.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use SimpleSAML\XML\Base64ElementTrait;
+
+/**
+ * Class representing a xenc:KA-Nonce element.
+ *
+ * @package simplesaml/xml-security
+ */
+final class KANonce extends AbstractXencElement
+{
+    use Base64ElementTrait;
+
+    /** @var string */
+    public const LOCALNAME = 'KA-Nonce';
+
+
+    /**
+     * @param string $content
+     */
+    public function __construct(string $content)
+    {
+        $this->setContent($content);
+    }
+}
diff --git a/src/XML/xenc/OriginatorKeyInfo.php b/src/XML/xenc/OriginatorKeyInfo.php
new file mode 100644
index 00000000..2f7db9a1
--- /dev/null
+++ b/src/XML/xenc/OriginatorKeyInfo.php
@@ -0,0 +1,71 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use DOMElement;
+use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Exception\InvalidDOMElementException;
+use SimpleSAML\XMLSecurity\Constants as C;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractKeyInfoType;
+use SimpleSAML\XMLSecurity\XML\ds\KeyName;
+use SimpleSAML\XMLSecurity\XML\ds\KeyValue;
+use SimpleSAML\XMLSecurity\XML\ds\RetrievalMethod;
+use SimpleSAML\XMLSecurity\XML\ds\X509Data;
+
+use function array_merge;
+
+/**
+ * Class representing a xenc:OriginatorKeyInfo element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+final class OriginatorKeyInfo extends AbstractKeyInfoType
+{
+    /** @var string */
+    public const NS = C::NS_XENC;
+
+    /** @var string */
+    public const NS_PREFIX = 'xenc';
+
+
+    /**
+     * Convert XML into a OriginatorKeyInfo
+     *
+     * @param \DOMElement $xml The XML element we should load
+     * @return static
+     *
+     * @throws \SimpleSAML\XML\Exception\InvalidDOMElementException
+     *   If the qualified name of the supplied element is wrong
+     */
+    public static function fromXML(DOMElement $xml): static
+    {
+        Assert::same($xml->localName, 'OriginatorKeyInfo', InvalidDOMElementException::class);
+        Assert::same($xml->namespaceURI, OriginatorKeyInfo::NS, InvalidDOMElementException::class);
+
+        $Id = self::getOptionalAttribute($xml, 'Id', null);
+
+        $keyName = KeyName::getChildrenOfClass($xml);
+        $keyValue = KeyValue::getChildrenOfClass($xml);
+        $retrievalMethod = RetrievalMethod::getChildrenOfClass($xml);
+        $x509Data = X509Data::getChildrenOfClass($xml);
+        //$pgpData = PGPData::getChildrenOfClass($xml);
+        //$spkiData = SPKIData::getChildrenOfClass($xml);
+        //$mgmtData = MgmtData::getChildrenOfClass($xml);
+        $other = self::getChildElementsFromXML($xml);
+
+        $info = array_merge(
+            $keyName,
+            $keyValue,
+            $retrievalMethod,
+            $x509Data,
+            //$pgpdata,
+            //$spkidata,
+            //$mgmtdata,
+            $other,
+        );
+
+        return new static($info, $Id);
+    }
+}
diff --git a/src/XML/xenc/P.php b/src/XML/xenc/P.php
new file mode 100644
index 00000000..a9f4a530
--- /dev/null
+++ b/src/XML/xenc/P.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use SimpleSAML\XML\Base64ElementTrait;
+
+/**
+ * Class representing a xenc:P element.
+ *
+ * @package simplesaml/xml-security
+ */
+final class P extends AbstractXencElement
+{
+    use Base64ElementTrait;
+
+
+    /**
+     * @param string $content
+     */
+    public function __construct(string $content)
+    {
+        $this->setContent($content);
+    }
+}
diff --git a/src/XML/xenc/PgenCounter.php b/src/XML/xenc/PgenCounter.php
new file mode 100644
index 00000000..5350a3c4
--- /dev/null
+++ b/src/XML/xenc/PgenCounter.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use SimpleSAML\XML\Base64ElementTrait;
+
+/**
+ * Class representing a xenc:pgenCounter element.
+ *
+ * @package simplesaml/xml-security
+ */
+final class PgenCounter extends AbstractXencElement
+{
+    use Base64ElementTrait;
+
+    /** @var string */
+    public const LOCALNAME = 'pgenCounter';
+
+
+    /**
+     * @param string $content
+     */
+    public function __construct(string $content)
+    {
+        $this->setContent($content);
+    }
+}
diff --git a/src/XML/xenc/Q.php b/src/XML/xenc/Q.php
new file mode 100644
index 00000000..379ecb54
--- /dev/null
+++ b/src/XML/xenc/Q.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use SimpleSAML\XML\Base64ElementTrait;
+
+/**
+ * Class representing a xenc:Q element.
+ *
+ * @package simplesaml/xml-security
+ */
+final class Q extends AbstractXencElement
+{
+    use Base64ElementTrait;
+
+
+    /**
+     * @param string $content
+     */
+    public function __construct(string $content)
+    {
+        $this->setContent($content);
+    }
+}
diff --git a/src/XML/xenc/RecipientKeyInfo.php b/src/XML/xenc/RecipientKeyInfo.php
new file mode 100644
index 00000000..c5eb61b9
--- /dev/null
+++ b/src/XML/xenc/RecipientKeyInfo.php
@@ -0,0 +1,71 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use DOMElement;
+use SimpleSAML\Assert\Assert;
+use SimpleSAML\XML\Exception\InvalidDOMElementException;
+use SimpleSAML\XMLSecurity\Constants as C;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractKeyInfoType;
+use SimpleSAML\XMLSecurity\XML\ds\KeyName;
+use SimpleSAML\XMLSecurity\XML\ds\KeyValue;
+use SimpleSAML\XMLSecurity\XML\ds\RetrievalMethod;
+use SimpleSAML\XMLSecurity\XML\ds\X509Data;
+
+use function array_merge;
+
+/**
+ * Class representing a xenc:RecipientKeyInfo element.
+ *
+ * @package simplesamlphp/xml-security
+ */
+final class RecipientKeyInfo extends AbstractKeyInfoType
+{
+    /** @var string */
+    public const NS = C::NS_XENC;
+
+    /** @var string */
+    public const NS_PREFIX = 'xenc';
+
+
+    /**
+     * Convert XML into a RecipientKeyInfo
+     *
+     * @param \DOMElement $xml The XML element we should load
+     * @return static
+     *
+     * @throws \SimpleSAML\XML\Exception\InvalidDOMElementException
+     *   If the qualified name of the supplied element is wrong
+     */
+    public static function fromXML(DOMElement $xml): static
+    {
+        Assert::same($xml->localName, 'RecipientKeyInfo', InvalidDOMElementException::class);
+        Assert::same($xml->namespaceURI, RecipientKeyInfo::NS, InvalidDOMElementException::class);
+
+        $Id = self::getOptionalAttribute($xml, 'Id', null);
+
+        $keyName = KeyName::getChildrenOfClass($xml);
+        $keyValue = KeyValue::getChildrenOfClass($xml);
+        $retrievalMethod = RetrievalMethod::getChildrenOfClass($xml);
+        $x509Data = X509Data::getChildrenOfClass($xml);
+        //$pgpData = PGPData::getChildrenOfClass($xml);
+        //$spkiData = SPKIData::getChildrenOfClass($xml);
+        //$mgmtData = MgmtData::getChildrenOfClass($xml);
+        $other = self::getChildElementsFromXML($xml);
+
+        $info = array_merge(
+            $keyName,
+            $keyValue,
+            $retrievalMethod,
+            $x509Data,
+            //$pgpdata,
+            //$spkidata,
+            //$mgmtdata,
+            $other,
+        );
+
+        return new static($info, $Id);
+    }
+}
diff --git a/src/XML/xenc/Seed.php b/src/XML/xenc/Seed.php
new file mode 100644
index 00000000..7eb7823a
--- /dev/null
+++ b/src/XML/xenc/Seed.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use SimpleSAML\XML\Base64ElementTrait;
+
+/**
+ * Class representing a xenc:seed element.
+ *
+ * @package simplesaml/xml-security
+ */
+final class Seed extends AbstractXencElement
+{
+    use Base64ElementTrait;
+
+    /** @var string */
+    public const LOCALNAME = 'seed';
+
+
+    /**
+     * @param string $content
+     */
+    public function __construct(string $content)
+    {
+        $this->setContent($content);
+    }
+}
diff --git a/src/XML/xenc/XencPublic.php b/src/XML/xenc/XencPublic.php
new file mode 100644
index 00000000..d8169c0e
--- /dev/null
+++ b/src/XML/xenc/XencPublic.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\XML\xenc;
+
+use SimpleSAML\XML\Base64ElementTrait;
+
+/**
+ * Class representing a xenc:Public element.
+ *
+ * @package simplesaml/xml-security
+ */
+final class XencPublic extends AbstractXencElement
+{
+    use Base64ElementTrait;
+
+    /** @var string */
+    public const LOCALNAME = 'Public';
+
+
+    /**
+     * @param string $content
+     */
+    public function __construct(string $content)
+    {
+        $this->setContent($content);
+    }
+}
diff --git a/tests/XML/ds/KeyInfoTest.php b/tests/XML/ds/KeyInfoTest.php
index e8e9f547..44e25513 100644
--- a/tests/XML/ds/KeyInfoTest.php
+++ b/tests/XML/ds/KeyInfoTest.php
@@ -13,6 +13,7 @@
 use SimpleSAML\XMLSecurity\Exception\InvalidArgumentException;
 use SimpleSAML\XMLSecurity\TestUtils\PEMCertificatesMock;
 use SimpleSAML\XMLSecurity\XML\ds\AbstractDsElement;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractKeyInfoType;
 use SimpleSAML\XMLSecurity\XML\ds\KeyInfo;
 use SimpleSAML\XMLSecurity\XML\ds\KeyName;
 use SimpleSAML\XMLSecurity\XML\ds\X509Certificate;
@@ -30,6 +31,7 @@
  * @package simplesamlphp/xml-security
  */
 #[CoversClass(AbstractDsElement::class)]
+#[CoversClass(AbstractKeyInfoType::class)]
 #[CoversClass(KeyInfo::class)]
 final class KeyInfoTest extends TestCase
 {
@@ -115,7 +117,7 @@ public function testMarshallingEmpty(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('ds:KeyInfo cannot be empty');
 
-        $keyInfo = new KeyInfo([]);
+        new KeyInfo([]);
     }
 
 
@@ -128,6 +130,6 @@ public function testUnmarshallingEmpty(): void
         $this->expectException(InvalidArgumentException::class);
         $this->expectExceptionMessage('ds:KeyInfo cannot be empty');
 
-        $keyInfo = KeyInfo::fromXML($document->documentElement);
+        KeyInfo::fromXML($document->documentElement);
     }
 }
diff --git a/tests/XML/xenc/AgreementMethodTest.php b/tests/XML/xenc/AgreementMethodTest.php
new file mode 100644
index 00000000..46ec79dd
--- /dev/null
+++ b/tests/XML/xenc/AgreementMethodTest.php
@@ -0,0 +1,220 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\XML\Chunk;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\{SerializableElementTestTrait, SchemaValidationTestTrait};
+use SimpleSAML\XMLSecurity\Constants as C;
+use SimpleSAML\XMLSecurity\TestUtils\PEMCertificatesMock;
+use SimpleSAML\XMLSecurity\Utils\XPath;
+use SimpleSAML\XMLSecurity\XML\ds\{DigestMethod, KeyName, X509Certificate, X509Data, X509SubjectName};
+use SimpleSAML\XMLSecurity\XML\xenc\{AbstractAgreementMethodType, AbstractXencElement};
+use SimpleSAML\XMLSecurity\XML\xenc\{AgreementMethod, KANonce, OriginatorKeyInfo, RecipientKeyInfo};
+
+use function dirname;
+use function openssl_x509_parse;
+use function str_replace;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\AgreementMethodTest
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(AbstractAgreementMethodType::class)]
+#[CoversClass(AgreementMethod::class)]
+final class AgreementMethodTest extends TestCase
+{
+    use SchemaValidationTestTrait;
+    use SerializableElementTestTrait;
+
+    /** @var string */
+    private static string $certificate;
+
+    /** @var string[] */
+    private static array $certData;
+
+
+    /**
+     */
+    public function setUp(): void
+    {
+        self::$testedClass = AgreementMethod::class;
+
+        self::$schemaFile = dirname(__FILE__, 4) . '/resources/schemas/xenc-schema.xsd';
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_AgreementMethod.xml',
+        );
+
+        self::$certificate = str_replace(
+            [
+                '-----BEGIN CERTIFICATE-----',
+                '-----END CERTIFICATE-----',
+                '-----BEGIN RSA PUBLIC KEY-----',
+                '-----END RSA PUBLIC KEY-----',
+                "\r\n",
+                "\n",
+            ],
+            [
+                '',
+                '',
+                '',
+                '',
+                "\n",
+                '',
+            ],
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+
+        self::$certData = openssl_x509_parse(
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $kaNonce = new KANonce('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $digestMethod = new DigestMethod(
+            C::DIGEST_SHA256,
+            [
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<some:Chunk xmlns:some="urn:x-simplesamlphp:namespace">some</some:Chunk>',
+                )->documentElement),
+            ],
+        );
+
+        $originatorKeyInfo = new OriginatorKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">originator</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed123',
+        );
+
+        $recipientKeyInfo = new RecipientKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">recipient</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed654',
+        );
+
+        $agreementMethod = new AgreementMethod(
+            C::XMLENC11_ECDH_ES,
+            $kaNonce,
+            $originatorKeyInfo,
+            $recipientKeyInfo,
+            [$digestMethod],
+        );
+
+        $this->assertEquals(
+            self::$xmlRepresentation->saveXML(self::$xmlRepresentation->documentElement),
+            strval($agreementMethod),
+        );
+    }
+
+
+    public function testMarshallingElementOrdering(): void
+    {
+        $kaNonce = new KANonce('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $digestMethod = new DigestMethod(
+            C::DIGEST_SHA256,
+            [
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<some:Chunk xmlns:some="urn:x-simplesamlphp:namespace">some</some:Chunk>',
+                )->documentElement),
+            ],
+        );
+
+        $originatorKeyInfo = new OriginatorKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">originator</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed321',
+        );
+
+        $recipientKeyInfo = new RecipientKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">recipient</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed654',
+        );
+
+        $agreementMethod = new AgreementMethod(
+            C::XMLENC11_ECDH_ES,
+            $kaNonce,
+            $originatorKeyInfo,
+            $recipientKeyInfo,
+            [$digestMethod],
+        );
+
+        // Marshall it to a \DOMElement
+        $agreementMethodElement = $agreementMethod->toXML();
+
+        $xpCache = XPath::getXPath($agreementMethodElement);
+
+        // Test for an KA-Nonce
+        /** @var \DOMElement[] $kaNonceElements */
+        $kaNonceElements = XPath::xpQuery($agreementMethodElement, './xenc:KA-Nonce', $xpCache);
+        $this->assertCount(1, $kaNonceElements);
+
+        // Test ordering of AgreementMethod contents
+        /** @var \DOMElement[] $agreementMethodElements */
+        $agreementMethodElements = XPath::xpQuery(
+            $agreementMethodElement,
+            './xenc:KA-Nonce/following-sibling::*',
+            $xpCache,
+        );
+
+        $this->assertCount(3, $agreementMethodElements);
+        $this->assertEquals('ds:DigestMethod', $agreementMethodElements[0]->tagName);
+        $this->assertEquals('xenc:OriginatorKeyInfo', $agreementMethodElements[1]->tagName);
+        $this->assertEquals('xenc:RecipientKeyInfo', $agreementMethodElements[2]->tagName);
+    }
+}
diff --git a/tests/XML/xenc/DHKeyValueTest.php b/tests/XML/xenc/DHKeyValueTest.php
new file mode 100644
index 00000000..7545a420
--- /dev/null
+++ b/tests/XML/xenc/DHKeyValueTest.php
@@ -0,0 +1,113 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SchemaValidationTestTrait;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Utils\XPath;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractDHKeyValueType;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\DHKeyValue;
+use SimpleSAML\XMLSecurity\XML\xenc\Generator;
+use SimpleSAML\XMLSecurity\XML\xenc\P;
+use SimpleSAML\XMLSecurity\XML\xenc\PgenCounter;
+use SimpleSAML\XMLSecurity\XML\xenc\Q;
+use SimpleSAML\XMLSecurity\XML\xenc\Seed;
+use SimpleSAML\XMLSecurity\XML\xenc\XencPublic;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\DHKeyValueTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractDHKeyValueType
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\DHKeyValue
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(AbstractDHKeyValueType::class)]
+#[CoversClass(DHKeyValue::class)]
+final class DHKeyValueTest extends TestCase
+{
+    use SchemaValidationTestTrait;
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = DHKeyValue::class;
+
+        self::$schemaFile = dirname(__FILE__, 4) . '/resources/schemas/xenc-schema.xsd';
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_DHKeyValue.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $xencPublic = new XencPublic('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $p = new P('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $q = new Q('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $generator = new Generator('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $seed = new Seed('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $pgenCounter = new PgenCounter('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $dhKeyValue = new DHKeyValue($xencPublic, $p, $q, $generator, $seed, $pgenCounter);
+
+        $this->assertEquals(
+            self::$xmlRepresentation->saveXML(self::$xmlRepresentation->documentElement),
+            strval($dhKeyValue),
+        );
+    }
+    /**
+     */
+    public function testMarshallingElementOrder(): void
+    {
+        $xencPublic = new XencPublic('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $p = new P('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $q = new Q('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $generator = new Generator('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $seed = new Seed('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+        $pgenCounter = new PgenCounter('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $dhKeyValue = new DHKeyValue($xencPublic, $p, $q, $generator, $seed, $pgenCounter);
+
+        // Marshall it to a \DOMElement
+        $dhKeyValueElement = $dhKeyValue->toXML();
+
+        $xpCache = XPath::getXPath($dhKeyValueElement);
+
+        // Test for an P
+        /** @var \DOMElement[] $pElements */
+        $pElements = XPath::xpQuery($dhKeyValueElement, './xenc:P', $xpCache);
+        $this->assertCount(1, $pElements);
+
+        // Test ordering of DHKeyValue contents
+        /** @var \DOMElement[] $dhKeyValueElements */
+        $dhKeyValueElements = XPath::xpQuery(
+            $dhKeyValueElement,
+            './xenc:P/following-sibling::*',
+            $xpCache,
+        );
+
+        $this->assertCount(5, $dhKeyValueElements);
+        $this->assertEquals('xenc:Q', $dhKeyValueElements[0]->tagName);
+        $this->assertEquals('xenc:Generator', $dhKeyValueElements[1]->tagName);
+        $this->assertEquals('xenc:Public', $dhKeyValueElements[2]->tagName);
+        $this->assertEquals('xenc:seed', $dhKeyValueElements[3]->tagName);
+        $this->assertEquals('xenc:pgenCounter', $dhKeyValueElements[4]->tagName);
+    }
+}
diff --git a/tests/XML/xenc/GeneratorTest.php b/tests/XML/xenc/GeneratorTest.php
new file mode 100644
index 00000000..eb7e6c0d
--- /dev/null
+++ b/tests/XML/xenc/GeneratorTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Test\XML\XMLDumper;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\Generator;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\GeneratorTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\Generator
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(Generator::class)]
+final class GeneratorTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = Generator::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_Generator.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $generator = new Generator('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $this->assertEquals(
+            XMLDumper::dumpDOMDocumentXMLWithBase64Content(self::$xmlRepresentation),
+            strval($generator),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingNotBase64(): void
+    {
+        $this->expectException(AssertionFailedException::class);
+        new Generator('/CTj3d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+    }
+}
diff --git a/tests/XML/xenc/KANonceTest.php b/tests/XML/xenc/KANonceTest.php
new file mode 100644
index 00000000..fb72c681
--- /dev/null
+++ b/tests/XML/xenc/KANonceTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Test\XML\XMLDumper;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\KANonce;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\KANonceTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\KANonce
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(KANonce::class)]
+final class KANonceTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = KANonce::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_KA-Nonce.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $kaNonce = new KANonce('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $this->assertEquals(
+            XMLDumper::dumpDOMDocumentXMLWithBase64Content(self::$xmlRepresentation),
+            strval($kaNonce),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingNotBase64(): void
+    {
+        $this->expectException(AssertionFailedException::class);
+        new KANonce('/CTj3d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+    }
+}
diff --git a/tests/XML/xenc/OriginatorKeyInfoTest.php b/tests/XML/xenc/OriginatorKeyInfoTest.php
new file mode 100644
index 00000000..69522d79
--- /dev/null
+++ b/tests/XML/xenc/OriginatorKeyInfoTest.php
@@ -0,0 +1,133 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\XML\Chunk;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Exception\InvalidArgumentException;
+use SimpleSAML\XMLSecurity\TestUtils\PEMCertificatesMock;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractDsElement;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractKeyInfoType;
+use SimpleSAML\XMLSecurity\XML\ds\KeyName;
+use SimpleSAML\XMLSecurity\XML\ds\X509Certificate;
+use SimpleSAML\XMLSecurity\XML\ds\X509Data;
+use SimpleSAML\XMLSecurity\XML\ds\X509SubjectName;
+use SimpleSAML\XMLSecurity\XML\xenc\OriginatorKeyInfo;
+
+use function dirname;
+use function openssl_x509_parse;
+use function str_replace;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\OriginatorKeyInfoTest
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractDsElement::class)]
+#[CoversClass(AbstractKeyInfoType::class)]
+#[CoversClass(OriginatorKeyInfo::class)]
+final class OriginatorKeyInfoTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /** @var string */
+    private static string $certificate;
+
+    /** @var string[] */
+    private static array $certData;
+
+
+    /**
+     */
+    public function setUp(): void
+    {
+        self::$testedClass = OriginatorKeyInfo::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_OriginatorKeyInfo.xml',
+        );
+
+        self::$certificate = str_replace(
+            [
+                '-----BEGIN CERTIFICATE-----',
+                '-----END CERTIFICATE-----',
+                '-----BEGIN RSA PUBLIC KEY-----',
+                '-----END RSA PUBLIC KEY-----',
+                "\r\n",
+                "\n",
+            ],
+            [
+                '',
+                '',
+                '',
+                '',
+                "\n",
+                '',
+            ],
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+
+        self::$certData = openssl_x509_parse(
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $originatorKeyInfo = new OriginatorKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">some</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed654',
+        );
+
+        $this->assertEquals(
+            self::$xmlRepresentation->saveXML(self::$xmlRepresentation->documentElement),
+            strval($originatorKeyInfo),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingEmpty(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('xenc:OriginatorKeyInfo cannot be empty');
+
+        new OriginatorKeyInfo([]);
+    }
+
+
+    /**
+     */
+    public function testUnmarshallingEmpty(): void
+    {
+        $document = DOMDocumentFactory::fromString(
+            '<xenc:OriginatorKeyInfo xmlns:xenc="' . OriginatorKeyInfo::NS . '"/>',
+        );
+
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('xenc:OriginatorKeyInfo cannot be empty');
+
+        OriginatorKeyInfo::fromXML($document->documentElement);
+    }
+}
diff --git a/tests/XML/xenc/PTest.php b/tests/XML/xenc/PTest.php
new file mode 100644
index 00000000..0e6c4cc8
--- /dev/null
+++ b/tests/XML/xenc/PTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Test\XML\XMLDumper;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\P;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\PTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\P
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(P::class)]
+final class PTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = P::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_P.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $p = new P('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $this->assertEquals(
+            XMLDumper::dumpDOMDocumentXMLWithBase64Content(self::$xmlRepresentation),
+            strval($p),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingNotBase64(): void
+    {
+        $this->expectException(AssertionFailedException::class);
+        new P('/CTj3d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+    }
+}
diff --git a/tests/XML/xenc/PgenCounterTest.php b/tests/XML/xenc/PgenCounterTest.php
new file mode 100644
index 00000000..bf5b9652
--- /dev/null
+++ b/tests/XML/xenc/PgenCounterTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Test\XML\XMLDumper;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\PgenCounter;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\PgenCounterTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\PgenCounter
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(PgenCounter::class)]
+final class PgenCounterTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = PgenCounter::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_pgenCounter.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $pgenCounter = new PgenCounter('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $this->assertEquals(
+            XMLDumper::dumpDOMDocumentXMLWithBase64Content(self::$xmlRepresentation),
+            strval($pgenCounter),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingNotBase64(): void
+    {
+        $this->expectException(AssertionFailedException::class);
+        new PgenCounter('/CTj3d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+    }
+}
diff --git a/tests/XML/xenc/PublicTest.php b/tests/XML/xenc/PublicTest.php
new file mode 100644
index 00000000..425979d3
--- /dev/null
+++ b/tests/XML/xenc/PublicTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Test\XML\XMLDumper;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\XencPublic;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\PublicTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\XencPublic
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(XencPublic::class)]
+final class PublicTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = XencPublic::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_Public.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $public = new XencPublic('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $this->assertEquals(
+            XMLDumper::dumpDOMDocumentXMLWithBase64Content(self::$xmlRepresentation),
+            strval($public),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingNotBase64(): void
+    {
+        $this->expectException(AssertionFailedException::class);
+        new XencPublic('/CTj3d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+    }
+}
diff --git a/tests/XML/xenc/QTest.php b/tests/XML/xenc/QTest.php
new file mode 100644
index 00000000..46ddcb12
--- /dev/null
+++ b/tests/XML/xenc/QTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Test\XML\XMLDumper;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\Q;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\QTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\Q
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(Q::class)]
+final class QTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = Q::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_Q.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $q = new Q('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $this->assertEquals(
+            XMLDumper::dumpDOMDocumentXMLWithBase64Content(self::$xmlRepresentation),
+            strval($q),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingNotBase64(): void
+    {
+        $this->expectException(AssertionFailedException::class);
+        new Q('/CTj3d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+    }
+}
diff --git a/tests/XML/xenc/RecipientKeyInfoTest.php b/tests/XML/xenc/RecipientKeyInfoTest.php
new file mode 100644
index 00000000..3fdce621
--- /dev/null
+++ b/tests/XML/xenc/RecipientKeyInfoTest.php
@@ -0,0 +1,133 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\XML\Chunk;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Exception\InvalidArgumentException;
+use SimpleSAML\XMLSecurity\TestUtils\PEMCertificatesMock;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractDsElement;
+use SimpleSAML\XMLSecurity\XML\ds\AbstractKeyInfoType;
+use SimpleSAML\XMLSecurity\XML\ds\KeyName;
+use SimpleSAML\XMLSecurity\XML\ds\X509Certificate;
+use SimpleSAML\XMLSecurity\XML\ds\X509Data;
+use SimpleSAML\XMLSecurity\XML\ds\X509SubjectName;
+use SimpleSAML\XMLSecurity\XML\xenc\RecipientKeyInfo;
+
+use function dirname;
+use function openssl_x509_parse;
+use function str_replace;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\RecipientKeyInfoTest
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractDsElement::class)]
+#[CoversClass(AbstractKeyInfoType::class)]
+#[CoversClass(RecipientKeyInfo::class)]
+final class RecipientKeyInfoTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /** @var string */
+    private static string $certificate;
+
+    /** @var string[] */
+    private static array $certData;
+
+
+    /**
+     */
+    public function setUp(): void
+    {
+        self::$testedClass = RecipientKeyInfo::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_RecipientKeyInfo.xml',
+        );
+
+        self::$certificate = str_replace(
+            [
+                '-----BEGIN CERTIFICATE-----',
+                '-----END CERTIFICATE-----',
+                '-----BEGIN RSA PUBLIC KEY-----',
+                '-----END RSA PUBLIC KEY-----',
+                "\r\n",
+                "\n",
+            ],
+            [
+                '',
+                '',
+                '',
+                '',
+                "\n",
+                '',
+            ],
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+
+        self::$certData = openssl_x509_parse(
+            PEMCertificatesMock::getPlainCertificate(PEMCertificatesMock::SELFSIGNED_CERTIFICATE),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $recipientKeyInfo = new RecipientKeyInfo(
+            [
+                new KeyName('testkey'),
+                new X509Data(
+                    [
+                        new X509Certificate(self::$certificate),
+                        new X509SubjectName(self::$certData['name']),
+                    ],
+                ),
+                new Chunk(DOMDocumentFactory::fromString(
+                    '<ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">some</ssp:Chunk>',
+                )->documentElement),
+            ],
+            'fed654',
+        );
+
+        $this->assertEquals(
+            self::$xmlRepresentation->saveXML(self::$xmlRepresentation->documentElement),
+            strval($recipientKeyInfo),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingEmpty(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('xenc:RecipientKeyInfo cannot be empty');
+
+        new RecipientKeyInfo([]);
+    }
+
+
+    /**
+     */
+    public function testUnmarshallingEmpty(): void
+    {
+        $document = DOMDocumentFactory::fromString(
+            '<xenc:RecipientKeyInfo xmlns:xenc="' . RecipientKeyInfo::NS . '"/>',
+        );
+
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('xenc:RecipientKeyInfo cannot be empty');
+
+        RecipientKeyInfo::fromXML($document->documentElement);
+    }
+}
diff --git a/tests/XML/xenc/SeedTest.php b/tests/XML/xenc/SeedTest.php
new file mode 100644
index 00000000..03a581f1
--- /dev/null
+++ b/tests/XML/xenc/SeedTest.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\XMLSecurity\Test\XML\xenc;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\Assert\AssertionFailedException;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSecurity\Test\XML\XMLDumper;
+use SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement;
+use SimpleSAML\XMLSecurity\XML\xenc\Seed;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\XMLSecurity\Test\XML\xenc\SeedTest
+ *
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\AbstractXencElement
+ * @covers \SimpleSAML\XMLSecurity\XML\xenc\Seed
+ *
+ * @package simplesamlphp/xml-security
+ */
+#[CoversClass(AbstractXencElement::class)]
+#[CoversClass(Seed::class)]
+final class SeedTest extends TestCase
+{
+    use SerializableElementTestTrait;
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = Seed::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 3) . '/resources/xml/xenc_seed.xml',
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $seed = new Seed('/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+
+        $this->assertEquals(
+            XMLDumper::dumpDOMDocumentXMLWithBase64Content(self::$xmlRepresentation),
+            strval($seed),
+        );
+    }
+
+
+    /**
+     */
+    public function testMarshallingNotBase64(): void
+    {
+        $this->expectException(AssertionFailedException::class);
+        new Seed('/CTj3d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=');
+    }
+}
diff --git a/tests/resources/xml/xenc_AgreementMethod.xml b/tests/resources/xml/xenc_AgreementMethod.xml
new file mode 100644
index 00000000..f4847ade
--- /dev/null
+++ b/tests/resources/xml/xenc_AgreementMethod.xml
@@ -0,0 +1,22 @@
+<xenc:AgreementMethod xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Algorithm="http://www.w3.org/2009/xmlenc11#ECDH-ES">
+  <xenc:KA-Nonce>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:KA-Nonce>
+  <ds:DigestMethod xmlns:ds="http://www.w3.org/2000/09/xmldsig#" Algorithm="http://www.w3.org/2001/04/xmlenc#sha256">
+    <some:Chunk xmlns:some="urn:x-simplesamlphp:namespace">some</some:Chunk>
+  </ds:DigestMethod>
+  <xenc:OriginatorKeyInfo Id="fed123">
+    <ds:KeyName xmlns:ds="http://www.w3.org/2000/09/xmldsig#">testkey</ds:KeyName>
+    <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+      <ds:X509Certificate>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</ds:X509Certificate>
+      <ds:X509SubjectName>/CN=selfsigned.simplesamlphp.org/O=SimpleSAMLphp HQ/L=Honolulu/ST=Hawaii/C=US</ds:X509SubjectName>
+    </ds:X509Data>
+    <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">originator</ssp:Chunk>
+  </xenc:OriginatorKeyInfo>
+  <xenc:RecipientKeyInfo Id="fed654">
+    <ds:KeyName xmlns:ds="http://www.w3.org/2000/09/xmldsig#">testkey</ds:KeyName>
+    <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+      <ds:X509Certificate>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</ds:X509Certificate>
+      <ds:X509SubjectName>/CN=selfsigned.simplesamlphp.org/O=SimpleSAMLphp HQ/L=Honolulu/ST=Hawaii/C=US</ds:X509SubjectName>
+    </ds:X509Data>
+    <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">recipient</ssp:Chunk>
+  </xenc:RecipientKeyInfo>
+</xenc:AgreementMethod>
diff --git a/tests/resources/xml/xenc_DHKeyValue.xml b/tests/resources/xml/xenc_DHKeyValue.xml
new file mode 100644
index 00000000..68e0969f
--- /dev/null
+++ b/tests/resources/xml/xenc_DHKeyValue.xml
@@ -0,0 +1,8 @@
+<xenc:DHKeyValue xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
+  <xenc:P>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:P>
+  <xenc:Q>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:Q>
+  <xenc:Generator>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:Generator>
+  <xenc:Public>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:Public>
+  <xenc:seed>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:seed>
+  <xenc:pgenCounter>/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:pgenCounter>
+</xenc:DHKeyValue>
diff --git a/tests/resources/xml/xenc_Generator.xml b/tests/resources/xml/xenc_Generator.xml
new file mode 100644
index 00000000..a87db221
--- /dev/null
+++ b/tests/resources/xml/xenc_Generator.xml
@@ -0,0 +1 @@
+<xenc:Generator xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:Generator>
diff --git a/tests/resources/xml/xenc_KA-Nonce.xml b/tests/resources/xml/xenc_KA-Nonce.xml
new file mode 100644
index 00000000..28552277
--- /dev/null
+++ b/tests/resources/xml/xenc_KA-Nonce.xml
@@ -0,0 +1 @@
+<xenc:KA-Nonce xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:KA-Nonce>
diff --git a/tests/resources/xml/xenc_OriginatorKeyInfo.xml b/tests/resources/xml/xenc_OriginatorKeyInfo.xml
new file mode 100644
index 00000000..080836d0
--- /dev/null
+++ b/tests/resources/xml/xenc_OriginatorKeyInfo.xml
@@ -0,0 +1,8 @@
+<xenc:OriginatorKeyInfo xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Id="fed654">
+  <ds:KeyName xmlns:ds="http://www.w3.org/2000/09/xmldsig#">testkey</ds:KeyName>
+  <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+    <ds:X509Certificate>MIICxDCCAi2gAwIBAgIUZ9QDx+SBFHednUWDFGm9tyVKrgQwDQYJKoZIhvcNAQELBQAwczElMCMGA1UEAwwcc2VsZnNpZ25lZC5zaW1wbGVzYW1scGhwLm9yZzEZMBcGA1UECgwQU2ltcGxlU0FNTHBocCBIUTERMA8GA1UEBwwISG9ub2x1bHUxDzANBgNVBAgMBkhhd2FpaTELMAkGA1UEBhMCVVMwIBcNMjIxMjAzMTAzNTQwWhgPMjEyMjExMDkxMDM1NDBaMHMxJTAjBgNVBAMMHHNlbGZzaWduZWQuc2ltcGxlc2FtbHBocC5vcmcxGTAXBgNVBAoMEFNpbXBsZVNBTUxwaHAgSFExETAPBgNVBAcMCEhvbm9sdWx1MQ8wDQYDVQQIDAZIYXdhaWkxCzAJBgNVBAYTAlVTMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDessdFRVDTMQQW3Na81B1CjJV1tmY3nopoIhZrkbDxLa+pv7jGDRcYreyu1DoQxEs06V2nHLoyOPhqJXSFivqtUwVYhR6NYgbNI6RRSsIJCweH0YOdlHna7gULPcLX0Bfbi4odStaFwG9yzDySwSEPtsKxm5pENPjNVGh+jJ+H/QIDAQABo1MwUTAdBgNVHQ4EFgQUvV75t8EoQo2fVa0E9otdtIGK5X0wHwYDVR0jBBgwFoAUvV75t8EoQo2fVa0E9otdtIGK5X0wDwYDVR0TAQH/BAUwAwEB/zANBgkqhkiG9w0BAQsFAAOBgQANQUeiwPJXkWMXuaDHToEBKcezYGqGEYnGUi9LMjeb+Kln7X8nn5iknlz4k77rWCbSwLPC/WDr0ySYQA+HagaeUaFpoiYFJKS6uFlK1HYWnM3W4PUiGHg1/xeZlMO44wTwybXVo0y9KMhchfB5XNbDdoJcqWYvi6xtmZZNRbxUyw==</ds:X509Certificate>
+    <ds:X509SubjectName>/CN=selfsigned.simplesamlphp.org/O=SimpleSAMLphp HQ/L=Honolulu/ST=Hawaii/C=US</ds:X509SubjectName>
+  </ds:X509Data>
+  <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">some</ssp:Chunk>
+</xenc:OriginatorKeyInfo>
diff --git a/tests/resources/xml/xenc_P.xml b/tests/resources/xml/xenc_P.xml
new file mode 100644
index 00000000..9c7ff0e6
--- /dev/null
+++ b/tests/resources/xml/xenc_P.xml
@@ -0,0 +1 @@
+<xenc:P xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:P>
diff --git a/tests/resources/xml/xenc_Public.xml b/tests/resources/xml/xenc_Public.xml
new file mode 100644
index 00000000..55f5b592
--- /dev/null
+++ b/tests/resources/xml/xenc_Public.xml
@@ -0,0 +1 @@
+<xenc:Public xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:Public>
diff --git a/tests/resources/xml/xenc_Q.xml b/tests/resources/xml/xenc_Q.xml
new file mode 100644
index 00000000..421da4f6
--- /dev/null
+++ b/tests/resources/xml/xenc_Q.xml
@@ -0,0 +1 @@
+<xenc:Q xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:Q>
diff --git a/tests/resources/xml/xenc_RecipientKeyInfo.xml b/tests/resources/xml/xenc_RecipientKeyInfo.xml
new file mode 100644
index 00000000..bee00ede
--- /dev/null
+++ b/tests/resources/xml/xenc_RecipientKeyInfo.xml
@@ -0,0 +1,8 @@
+<xenc:RecipientKeyInfo xmlns:xenc="http://www.w3.org/2001/04/xmlenc#" Id="fed654">
+  <ds:KeyName xmlns:ds="http://www.w3.org/2000/09/xmldsig#">testkey</ds:KeyName>
+  <ds:X509Data xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
+    <ds:X509Certificate>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</ds:X509Certificate>
+    <ds:X509SubjectName>/CN=selfsigned.simplesamlphp.org/O=SimpleSAMLphp HQ/L=Honolulu/ST=Hawaii/C=US</ds:X509SubjectName>
+  </ds:X509Data>
+  <ssp:Chunk xmlns:ssp="urn:x-simplesamlphp:namespace">some</ssp:Chunk>
+</xenc:RecipientKeyInfo>
diff --git a/tests/resources/xml/xenc_pgenCounter.xml b/tests/resources/xml/xenc_pgenCounter.xml
new file mode 100644
index 00000000..f56ccdd4
--- /dev/null
+++ b/tests/resources/xml/xenc_pgenCounter.xml
@@ -0,0 +1 @@
+<xenc:pgenCounter xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:pgenCounter>
diff --git a/tests/resources/xml/xenc_seed.xml b/tests/resources/xml/xenc_seed.xml
new file mode 100644
index 00000000..019a5caf
--- /dev/null
+++ b/tests/resources/xml/xenc_seed.xml
@@ -0,0 +1 @@
+<xenc:seed xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">/CTj03d1DB5e2t7CTo9BEzCf5S9NRzwnBgZRlm32REI=</xenc:seed>