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Verify RSA host key signatures by encoding - #1359
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wolfSSH_RsaVerify() now returns WS_RSA_E when the signature is longer than the modulus, so trailing bytes after a valid signature no longer verify. A shorter signature is still left-padded with zeros. - tests: unit test with one byte appended to a valid signature
DoKexDhReply() now checks an RSA host key signature over H the same way userauth does: it hashes H, encodes the DigestInfo, and compares whole blocks with wolfSSH_RsaVerify() per RFC 8332 Section 5.3, in place of wc_SignatureVerify(). This also restores ssh-rsa host keys on wolfSSL 5.9.2 and later, which refuse SHA-1 in wc_SignatureVerify(). - tests: ssh-rsa host key handshake, valid and corrupted signature - tests: host key signature with a trailing byte is rejected Issue: F-17075
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🟢 Approval recommended
No active review issues block approval of the RSA host key verification changes.
No open issues 🎉
What changed in this PR
This PR restores ssh-rsa host key verification with wolfSSL 5.9.2 and later by using encoded DigestInfo comparison, consistent with user authentication.
Changes:
- Replaces RSA host key verification with hashing, DigestInfo encoding, and
wolfSSH_RsaVerify(). - Rejects RSA signatures longer than the key modulus.
- Adds handshake and unit coverage for valid, corrupted, and overlong signatures.
| File | Description |
|---|---|
| tests/unit.c | Tests rejection of RSA signatures with an appended byte. |
| tests/regress.c | Adds valid and corrupted ssh-rsa handshake tests and an overlong RSA signature test. |
| src/internal.c | Uses encoded DigestInfo for RSA host key verification and rejects overlong signatures. |
Review effort: Balanced
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Fenrir Automated Review — PR #1359
Scan targets checked: wolfssh-src, wolfssh-bugs
Coverage: 3 of 3 in-scope changed file(s) opened by the reviewer
Fenrir result: Approved ✅
No new issues found in the changed files.
Advisory only — this automated result does not count as a GitHub approval.
Review tier: Lite
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DoKexDhReply() checks an RSA host key signature by encoding the
DigestInfo and comparing whole blocks, as userauth does (RFC 8332
Section 5.3). This restores ssh-rsa host keys on wolfSSL 5.9.2 and up.
over-long signatures
Issue: F-17075