`rnpkeys --import` rejects an OpenPGP certificate with a signature with an unknown subpacket unless i use `--permissive`

dkg commented 2 months ago

This OpenPGP certificate contains a "1st party approved 3rd party certifications" (1pa3pc) signature over its User ID:

When i try to import it with rnpkeys, i get a failure:

$ rnpkeys --import test.cert
[parse() ./src/librepgp/stream-sig.cpp:405] unknown subpacket : 37
[parse_v4() ./src/librepgp/stream-sig.cpp:1290] failed to parse hashed subpackets
[process_pgp_key_signatures() ./src/librepgp/stream-key.cpp:243] failed to parse signature at 422
failed to import key(s) from -, stopping.
Import finished: 0 keys processed, 0 new public keys, 0 new secret keys, 0 updated, 0 unchanged.
$ rnpkeys --version
rnp 0.17.0-3
Ribose Inc. <rnpgp@ribose.com>
Backend: Botan
Backend version: 2.19.4
Supported algorithms:
Public key:  RSA, ELGAMAL, DSA, ECDH, ECDSA, EDDSA, SM2
Encryption:  IDEA, TRIPLEDES, CAST5, BLOWFISH, AES128, AES192, AES256, TWOFISH, CAMELLIA128, CAMELLIA192, CAMELLIA256, SM4
AEAD:  None, EAX, OCB
Key protection:  CFB
Hash:  MD5, SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224, SHA3-256, SHA3-512, SM3
Compression:  Uncompressed, ZIP, ZLIB, BZip2
Curves:  NIST P-256, NIST P-384, NIST P-521, Ed25519, Curve25519, brainpoolP256r1, brainpoolP384r1, brainpoolP512r1, secp256k1, SM2 P-256
Please report security issues at (https://www.rnpgp.org/feedback) and
general bugs at https://github.com/rnpgp/rnp/issues.
$

If i try to import it without the 1pa3pc selfsig, rnpkeys imports it just fine. Likewise, if i import it with rnpkeys --import --permissive test.cert it also

rnpkeys being brittle here presents a challenge to the whole ecosystem for deploying any new kind of signature or subpacket.

I think this is related to #2204 -- it is almost certainly a similar policy issue.

ni4 commented 2 months ago

Hi, thanks for letting us know. Yeah, here by default we reject unknown subpacket and signature which includes it, being stricter by default. However user may ignore this error via the CLI (or FFI for API user).

kaie commented 1 month ago

Why is the subpacket type 37 marked as critical? If you want it to be ignored by implementations that don't understand it, shouldn't it be marked non-critical?

dkg commented 1 month ago

The subpacket is marked as critical because if you don't understand that kind of subpacket, you should not be accepting that kind of signature.

But, if you ignore this signature (or treat it as invalid), the remaining certificate is still just fine. Rejecting the whole certificate because one signature in it is invalid -- even though you would have accepted the entire certificate had that signature not been there -- this is what makes the implementation unnecessarily brittle. And that brittleness makes it harder to improve the ecosystem as a whole, because implementations (including RNP!) can't deploy newer parts of OpenPGP without worrying that old versions of RNP will choke when they see these things.

rnpgp / rnp

`rnpkeys --import` rejects an OpenPGP certificate with a signature with an unknown subpacket unless i use `--permissive` #2223