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Reject weak Ed25519 keys in CasePack checkpoint verification #103

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Merged
EauDoon merged 1 commit into from
Oct 2, 2026
Merged

Reject weak Ed25519 keys in CasePack checkpoint verification #103

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8 changes: 2 additions & 6 deletions src/casepack/validate.ts
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Original file line number Diff line number Diff line change
@@ -1,8 +1,5 @@
import { Buffer } from "node:buffer";
import {
createPublicKey,
type JsonWebKeyInput,
} from "node:crypto";
import { jwkThumbprint } from "../crypto.js";
import {
isSha256Digest,
} from "../canonical.js";
Expand Down Expand Up @@ -388,8 +385,7 @@ function validatePublicJwk(value: unknown, path: string, issues: ValidationIssue
return false;
}
try {
const key = createPublicKey({ key: value as unknown as JsonWebKeyInput["key"], format: "jwk" });
if (key.asymmetricKeyType !== "ed25519") throw new TypeError("Unexpected key type");
jwkThumbprint(value as unknown as Ed25519PublicJwk);
} catch {
addIssue(issues, path, "MBCP_SCHEMA_INVALID", "External public key is malformed");
return false;
Expand Down
31 changes: 31 additions & 0 deletions test/casepack-v11.test.mjs
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Expand Up @@ -790,6 +790,37 @@ test("caller-pinned external trust verifies a signed source checkpoint without e
assert.equal(report.coverageStatus, "satisfied");
assert.equal(report.nativeBundle.trustChecked, false);

// Identity-point public keys permit R=identity, S=0 without a private key.
// Pinning such a snapshot must not turn this forgery into source evidence.
const identity = Buffer.alloc(32);
identity[0] = 1;
const identitySnapshot = sealExternalTrustSnapshot({
...externalTrustSnapshot,
keys: [{
...externalTrustSnapshot.keys[0],
publicJwk: { kty: "OKP", crv: "Ed25519", x: identity.toString("base64url") },
}],
snapshotDigest: undefined,
});
const forgedCheckpoint = {
...checkpoint,
proofs: [{
...checkpoint.proofs[0],
signature: Buffer.concat([identity, Buffer.alloc(32)]).toString("base64url"),
}],
};
const identityReport = verifyMandateBoundCasePack(
resealPack({
...candidate,
externalTrustSnapshot: identitySnapshot,
sourceCheckpoints: [forgedCheckpoint],
}),
{ ...anchors, externalTrustSnapshotDigest: identitySnapshot.snapshotDigest },
);
assert.equal(identityReport.valid, false);
assert.ok(identityReport.issues.some((issue) =>
issue.code === "MBCP_SCHEMA_INVALID" && issue.path.endsWith(".publicJwk")));

const lateKeySnapshot = sealExternalTrustSnapshot({
...externalTrustSnapshot,
keys: [{
Expand Down
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