diff --git a/js-src/IdentityAssertion.spec.ts b/js-src/IdentityAssertion.spec.ts
index 0b1221a..50d993f 100644
--- a/js-src/IdentityAssertion.spec.ts
+++ b/js-src/IdentityAssertion.spec.ts
@@ -16,7 +16,7 @@
 import type { Manifest } from "@contentauth/c2pa-types";
 import * as fs from "fs-extra";
 import * as crypto from "crypto";
-import { encode } from "cbor2";
+import { encode, Tag } from "cbor2";
 
 import type {
   JsCallbackSignerConfig,
@@ -41,14 +41,69 @@ class TestSigner {
     sign.end();
     return sign.sign(this.privateKey);
   };
+
+  signP1363 = async (bytes: Buffer): Promise<Buffer> => {
+    const sign = crypto.createSign("SHA256");
+    sign.update(bytes);
+    sign.end();
+    return sign.sign({ key: this.privateKey, dsaEncoding: "ieee-p1363" });
+  };
 }
 
-class TestCawgSigner {
-  constructor(private manifestSigner: TestSigner) {}
+/**
+ * COSE_Sign1 credential holder for cawg.x509.cose identity assertions.
+ *
+ * The sig_type "cawg.x509.cose" requires the credential holder callback to
+ * return a complete COSE_Sign1 envelope (RFC 9052), not a raw signature.
+ *
+ * Protocol:
+ * 1. CBOR-encode the SignerPayload → detached payload
+ * 2. Build protected header { 1: alg_id } as CBOR bstr
+ * 3. Build Sig_structure = ["Signature1", protected, external_aad, payload]
+ * 4. Sign CBOR(Sig_structure) with IEEE P1363 format (COSE requirement)
+ * 5. Return CBOR(Tag(18, [protected, {}, nil, signature]))
+ *
+ * IMPORTANT: Use Uint8Array (not Buffer) for byte strings passed to cbor2's
+ * encode(). Buffer causes cbor2 to unwrap CBOR content instead of encoding
+ * it as a bstr, which produces "got map, expected bstr" errors in the
+ * COSE parser.
+ */
+class CoseCawgSigner {
+  private static readonly ES256_ALG_ID = -7;
+
+  constructor(private signer: TestSigner) {}
 
   sign = async (payload: SignerPayload): Promise<Buffer> => {
-    const cborBytes = Buffer.from(encode(payload));
-    return this.manifestSigner.sign(cborBytes);
+    // CBOR-encode the SignerPayload (detached content)
+    const payloadCbor = new Uint8Array(encode(payload));
+
+    // Protected header: { 1: -7 } (alg = ES256) — must be Uint8Array for bstr
+    const protectedBytes = new Uint8Array(
+      encode(new Map([[1, CoseCawgSigner.ES256_ALG_ID]])),
+    );
+
+    // Sig_structure per RFC 9052 §4.4
+    const sigStructure = [
+      "Signature1",
+      protectedBytes,
+      new Uint8Array(0), // external_aad
+      payloadCbor,
+    ];
+    const sigStructureCbor = Buffer.from(encode(sigStructure));
+
+    // Sign with IEEE P1363 format (required by COSE ES256)
+    const rawSignature = new Uint8Array(
+      await this.signer.signP1363(sigStructureCbor),
+    );
+
+    // COSE_Sign1 = Tag(18, [protected, unprotected, payload(nil), signature])
+    const coseSign1 = new Tag(18, [
+      protectedBytes,
+      new Map(),
+      null,
+      rawSignature,
+    ]);
+    return Buffer.from(encode(coseSign1));
   };
 }
 
@@ -123,9 +178,9 @@ describe("IdentityAssertionBuilder", () => {
       "./tests/fixtures/certs/es256.pem",
     );
     const c2paPublicKey = await fs.readFile("./tests/fixtures/certs/es256.pub");
-    // Use the same signer for both C2PA manifest and COSE signing
 
-    // Create signer configurations
+    // Create signer configurations — use directCoseHandling: false with P1363
+    // signatures for the manifest signer
     const c2paConfig: JsCallbackSignerConfig = {
       alg: "es256" as SigningAlg,
       certs: [c2paPublicKey],
@@ -133,20 +188,22 @@ describe("IdentityAssertionBuilder", () => {
       tsaUrl: undefined,
       tsaHeaders: undefined,
       tsaBody: undefined,
-      directCoseHandling: true,
+      directCoseHandling: false,
     };
 
     // Create signers
     const c2paTestSigner = new TestSigner(c2paPrivateKey);
     const c2paSigner = CallbackSigner.newSigner(
       c2paConfig,
-      c2paTestSigner.sign,
+      c2paTestSigner.signP1363,
     );
-    const cawgTestSigner = new TestCawgSigner(c2paTestSigner);
+
+    // COSE_Sign1 credential holder — returns a proper COSE envelope
+    const coseSigner = new CoseCawgSigner(c2paTestSigner);
     const cawgSigner = CallbackCredentialHolder.newCallbackCredentialHolder(
       10000,
       "cawg.x509.cose",
-      cawgTestSigner.sign,
+      coseSigner.sign,
     );
 
     const source = {
@@ -183,9 +240,27 @@ describe("IdentityAssertionBuilder", () => {
     await builder.signAsync(iaSigner, source, dest);
 
     // Verify the manifest
-    await Reader.fromAsset({
+    const reader = await Reader.fromAsset({
       buffer: dest.buffer! as Buffer,
       mimeType: "image/jpeg",
     });
+
+    // Verify cawg.identity assertion is present
+    const active = reader!.getActive() as any;
+    const assertions: string[] =
+      active?.assertions?.map((a: any) => a.label) ?? [];
+    expect(assertions).toContain("cawg.identity");
+
+    // Verify no integrity errors (trust warnings from self-signed certs are OK)
+    const store = reader!.json() as any;
+    const validationStatus: Array<{ code: string }> =
+      store?.validation_status ?? [];
+    const integrityErrors = validationStatus.filter(
+      (s) =>
+        !s.code.startsWith("signingCredential.") &&
+        !s.code.startsWith("trust.") &&
+        !s.code.startsWith("certificate."),
+    );
+    expect(integrityErrors).toHaveLength(0);
   });
 });