feat(ext/sw): sshsig — SSHSIG framing over sign_for_git for git-valid commit signatures

extension/src/service-worker/__tests__/sshsig.test.ts

@@ -0,0 +1,114 @@
+import { createPrivateKey, sign as nodeSign } from 'node:crypto';
+import { describe, expect, test } from 'vitest';
+import { buildSshSig } from '../sshsig';
+
+// ---------------------------------------------------------------------------
+// Fixed-seed deterministic ed25519 signer (Node-only; test-only).
+// sshsig.ts itself uses only Web APIs — the signer is injected.
+// ---------------------------------------------------------------------------
+
+const SEED_HEX =
+  '000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f';
+
+const PUB_OPENSSH =
+  'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAOhB7/zzhC+HXDdGOdLwJln5NYwm6UNXx3chmQSVTG4';
+
+const PAYLOAD =
+  'tree 4b825dc642cb6eb9a060e54bf8d69288fbee4904\nauthor Owner <o@acme> 1750000000 +0000\ncommitter Owner <o@acme> 1750000000 +0000\n\norg add\n';
+
+// Byte-exact golden vector — already confirmed against real `git verify-commit`.
+const GOLDEN_ARMOR =
+  '-----BEGIN SSH SIGNATURE-----\n' +
+  'U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgA6EHv/POEL4dcN0Y50vAmWfk1j\n' +
+  'CbpQ1fHdyGZBJVMbgAAAADZ2l0AAAAAAAAAAZzaGE1MTIAAABTAAAAC3NzaC1lZDI1NTE5\n' +
+  'AAAAQFLDkEyykOw6Z+I9qLKtTDToj2pXIfgvn+PoNDa5PfE6DQ/BmetpymL2aVdQXSpQ4k\n' +
+  'i4fjWKgx63Q43NsyR/cAs=\n' +
+  '-----END SSH SIGNATURE-----';
+
+function fixedSigner() {
+  const pkcs8 = Buffer.concat([
+    Buffer.from('302e020100300506032b657004220420', 'hex'),
+    Buffer.from(SEED_HEX, 'hex'),
+  ]);
+  const key = createPrivateKey({ key: pkcs8, format: 'der', type: 'pkcs8' });
+  return (data: Uint8Array) =>
+    new Uint8Array(nodeSign(null, Buffer.from(data), key));
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+describe('buildSshSig', () => {
+  test('matches the golden vector byte-for-byte (synchronous rawSign)', async () => {
+    const armor = await buildSshSig(
+      new TextEncoder().encode(PAYLOAD),
+      PUB_OPENSSH,
+      fixedSigner(),
+    );
+    expect(armor).toBe(GOLDEN_ARMOR);
+  });
+
+  test('matches the golden vector when rawSign returns a Promise (async rawSign)', async () => {
+    const syncSigner = fixedSigner();
+    const asyncSigner = (data: Uint8Array): Promise<Uint8Array> =>
+      Promise.resolve(syncSigner(data));
+    const armor = await buildSshSig(
+      new TextEncoder().encode(PAYLOAD),
+      PUB_OPENSSH,
+      asyncSigner,
+    );
+    expect(armor).toBe(GOLDEN_ARMOR);
+  });
+
+  test('structural: armor has correct PEM markers and SSHSIG binary header', async () => {
+    const armor = await buildSshSig(
+      new TextEncoder().encode(PAYLOAD),
+      PUB_OPENSSH,
+      fixedSigner(),
+    );
+
+    expect(armor.startsWith('-----BEGIN SSH SIGNATURE-----')).toBe(true);
+    expect(armor.endsWith('-----END SSH SIGNATURE-----')).toBe(true);
+
+    // Extract and decode the base64 body (lines between the markers).
+    const lines = armor.split('\n');
+    const body = lines.slice(1, lines.length - 1).join('');
+    const decoded = Uint8Array.from(atob(body), (c) => c.charCodeAt(0));
+
+    // First 6 bytes must be ASCII "SSHSIG".
+    const header = new TextDecoder().decode(decoded.slice(0, 6));
+    expect(header).toBe('SSHSIG');
+
+    // Bytes 6-9: u32be version = 1.
+    const version = new DataView(decoded.buffer).getUint32(6, false);
+    expect(version).toBe(1);
+
+    // The namespace string "git" must appear as a length-prefixed field.
+    // str("git") = [0,0,0,3,0x67,0x69,0x74]
+    const gitBytes = new Uint8Array([0, 0, 0, 3, 0x67, 0x69, 0x74]);
+    let foundGit = false;
+    for (let i = 0; i <= decoded.length - gitBytes.length; i++) {
+      if (gitBytes.every((b, j) => decoded[i + j] === b)) {
+        foundGit = true;
+        break;
+      }
+    }
+    expect(foundGit).toBe(true);
+  });
+
+  test('determinism/sensitivity: different payload produces different armor', async () => {
+    const signer = fixedSigner();
+    const armor1 = await buildSshSig(
+      new TextEncoder().encode(PAYLOAD),
+      PUB_OPENSSH,
+      signer,
+    );
+    const armor2 = await buildSshSig(
+      new TextEncoder().encode(PAYLOAD + ' modified'),
+      PUB_OPENSSH,
+      signer,
+    );
+    expect(armor1).not.toBe(armor2);
+  });
+});