Dispatch recipients on bech32 HRP instead of string prefixes

Age.Cli/AgeCommand.cs

@@ -132,21 +132,8 @@ private static List<IIdentity> CollectDecryptIdentities(bool passphrase, string[
         _ => null
     };
 
-    private static IRecipient ParseRecipient(string s)
-    {
-        var callbacks = new CliPluginCallbacks();
-
-        if (s.StartsWith("age1pq"))
-            return MlKem768X25519Recipient.Parse(s);
-        if (s.StartsWith("age1") && s.IndexOf('1', 4) > 0)
-            return new PluginRecipient(s, callbacks);
-        if (s.StartsWith("age1"))
-            return X25519Recipient.Parse(s);
-        if (s.StartsWith("ssh-"))
-            return AgeKeygen.ParseSshRecipient(s);
-
-        throw new FormatException($"unknown recipient type: {s}");
-    }
+    private static IRecipient ParseRecipient(string s) =>
+        AgeKeygen.ParseRecipientLine(s, new CliPluginCallbacks());
 
     private static List<IIdentity> LoadIdentities(string path, IPluginCallbacks callbacks)
     {

Age.Tests/RecipientsFileTests.cs

@@ -1,11 +1,17 @@
 using Age;
+using Age.Crypto;
 using Age.Recipients;
 using Xunit;
 
 namespace Age.Tests;
 
 public class RecipientsFileTests
 {
+    // Found by brute force: a real X25519 key whose recipient's bech32 data happens to start
+    // with "pq", so the string begins "age1pq" exactly like an ML-KEM-768 recipient does.
+    private const string PqLookalikeIdentity = "AGE-SECRET-KEY-1LRKLPKJT609NGXMQ8FJ2T985FU95PK29M9YZRPAW4WWZ5WWZWFRSNV7M2H";
+    private const string PqLookalikeRecipient = "age1pqw26wvuhkqsmmqh0flpkkt7hmn2mrwmr83v84fm8zjmalnqavuq2tj4sg";
+
     [Fact]
     public void ParseRecipientsFile_X25519()
     {
@@ -75,7 +81,44 @@ public void ParseRecipientsFile_UnrecognizedLine_Throws()
     {
         var text = "NOT-A-VALID-RECIPIENT\n";
         var ex = Assert.Throws<FormatException>(() => AgeKeygen.ParseRecipientsFile(text));
-        Assert.Contains("unrecognized line", ex.Message);
+        Assert.Contains("unrecognized recipient", ex.Message);
+    }
+
+    [Fact]
+    public void ParseRecipientsFile_X25519StartingWithAge1Pq_ParsesAsX25519()
+    {
+        using var identity = X25519Identity.Parse(PqLookalikeIdentity);
+        Assert.Equal(PqLookalikeRecipient, identity.Recipient.ToString());
+
+        var parsed = AgeKeygen.ParseRecipientsFile($"{PqLookalikeRecipient}\n");
+        Assert.Single(parsed);
+        Assert.IsType<X25519Recipient>(parsed[0]);
+    }
+
+    [Fact]
+    public void ParseRecipientsFile_X25519StartingWithAge1Pq_RoundTrips()
+    {
+        using var identity = X25519Identity.Parse(PqLookalikeIdentity);
+        var recipients = AgeKeygen.ParseRecipientsFile($"{PqLookalikeRecipient}\n");
+        var plaintext = "pq-lookalike recipient"u8.ToArray();
+
+        using var encInput = new MemoryStream(plaintext);
+        using var encOutput = new MemoryStream();
+        AgeEncrypt.Encrypt(encInput, encOutput, recipients.ToArray());
+
+        encOutput.Position = 0;
+        using var decOutput = new MemoryStream();
+        AgeEncrypt.Decrypt(encOutput, decOutput, identity);
+        Assert.Equal(plaintext, decOutput.ToArray());
+    }
+
+    [Fact]
+    public void ParseRecipientsFile_PluginNameStartingWithPq_ParsesAsPlugin()
+    {
+        var recipient = Bech32.Encode("age1pqtest", [0x01, 0x02, 0x03]);
+        var parsed = AgeKeygen.ParseRecipientsFile($"{recipient}\n");
+        Assert.Single(parsed);
+        Assert.IsType<PluginRecipient>(parsed[0]);
     }
 
     [Fact]

Age/Age.csproj

@@ -29,6 +29,7 @@
 
   <ItemGroup>
     <InternalsVisibleTo Include="Age.Tests" />
+    <InternalsVisibleTo Include="Age.Cli" />
   </ItemGroup>
 
   <ItemGroup>

Age/AgeKeygen.cs

@@ -68,14 +68,26 @@ public static IReadOnlyList<IRecipient> ParseRecipientsFile(string text, IPlugin
             .Select(line => ParseRecipientLine(line, callbacks))
             .ToList();
 
-    private static IRecipient ParseRecipientLine(string line, IPluginCallbacks? callbacks) => line switch
+    /// <summary>
+    /// Parses a single recipient string: age X25519, ML-KEM-768, plugin, or SSH public key.
+    /// </summary>
+    internal static IRecipient ParseRecipientLine(string line, IPluginCallbacks? callbacks)
     {
-        _ when line.StartsWith("age1pq") => MlKem768X25519Recipient.Parse(line),
-        _ when line.StartsWith("age1") && line.IndexOf('1', 4) > 0 => new PluginRecipient(line, callbacks),
-        _ when line.StartsWith("age1") => X25519Recipient.Parse(line),
-        _ when line.StartsWith("ssh-") => ParseSshRecipient(line),
-        _ => throw new FormatException($"unrecognized line in recipients file: {line}")
-    };
+        // Dispatch on the true bech32 HRP — everything before the LAST '1' (BIP-173), since
+        // data never contains '1'. String prefixes are ambiguous here: 'p' and 'q' are data
+        // characters, so an X25519 recipient's data can itself start with "pq" ("age1pq...").
+        var sep = line.LastIndexOf('1');
+        var hrp = sep > 0 ? line[..sep] : "";
+
+        return hrp switch
+        {
+            "age" => X25519Recipient.Parse(line),
+            "age1pq" => MlKem768X25519Recipient.Parse(line),
+            _ when hrp.StartsWith("age1") => new PluginRecipient(line, callbacks),
+            _ when line.StartsWith("ssh-") => ParseSshRecipient(line),
+            _ => throw new FormatException($"unrecognized recipient: {line}")
+        };
+    }
 
     /// <summary>
     /// Parses a plaintext identity file containing AGE-SECRET-KEY lines, plugin identities, comments, and blank lines.