CMS SignedData

sm-crypto-wasm/cms provides CMS SignedData signing and verification with SM2:

• detached (default) and attached modes;
• builds the contentType / messageDigest / signingTime signed attributes;
• verifies over the original DER bytes of signedAttrs, never re-encoding;
• accepts BER indefinite-length input;
• returns structured failure reasons.

Only SignedData is implemented — no EnvelopedData or RFC 3161 timestamps, and no trust-chain building. Certificate validity, usage and CRL/OCSP checks are the caller's responsibility.

Signing

import { cms, sm2, sm3 } from 'sm-crypto-wasm';

await sm2.ensureLoaded();
await sm3.ensureLoaded();

const signed = cms.signData({
  data: 'message',                // strings are encoded as UTF-8 (not hex/base64)
  privateKey: privateKeyPem,
  certificate: certificatePem,    // signer certificate
  certificates: [caPem],          // optional extra chain certificates
  detached: true,                 // default
  signingTime: new Date(),        // default now; false to omit
});

signed.der;     // Uint8Array
signed.pem;     // -----BEGIN CMS-----
signed.base64;

The signer identifier is issuerAndSerialNumber, taken from the signer certificate.

Verification

const result = cms.verifySignedData(signed.der, {
  detachedData: 'message',
  certificates: [extraPem],       // optional extra candidates
});

result.valid;                     // true only if every signer is valid
result.signers[0]?.valid;
result.signers[0]?.certificate;
result.signers[0]?.signingTime;
result.signers[0]?.errorCode;
result.signers[0]?.error;

errorCode:

Value	Meaning
NO_CERTIFICATE	the signer certificate is neither embedded nor supplied
DIGEST_MISMATCH	messageDigest / contentType does not match the content
SIGNATURE_INVALID	malformed signature value or failed SM2 verification
UNSUPPORTED_ALGORITHM	digest/signature algorithm is not SM3 / SM3withSM2
MALFORMED	malformed CMS, or detached mode without detachedData

Completely unparseable input returns a MALFORMED result instead of throwing; environment errors such as unloaded wasm still throw.

Input formats

verifySignedData / parseSignedData accept:

• PEM (-----BEGIN CMS----- or -----BEGIN PKCS7-----);
• base64 / hex;
• DER or BER bytes.

User id

CMS signing uses the empty SM2 user id by default, matching OpenSSL's CMS path. For the GM/T default id:

import { DEFAULT_SM2_USER_ID } from 'sm-crypto-wasm/x509';

cms.signData({ data, privateKey, certificate, userID: DEFAULT_SM2_USER_ID });
cms.verifySignedData(der, { detachedData: data, userID: DEFAULT_SM2_USER_ID });

When userID is omitted during verification, the empty id is tried first and the GM/T default second.

Security boundaries

• verifies only that the signature matches the content — not that the certificate is trusted; callers must perform chain / policy / validity checks;
• certificate usage is not checked;
• signData neither generates nor manages private keys.