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Issue better error message for invalid OpenPGP RSA keys
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During testing of RNP's OpenSSL backend got to the case when GnuPG randomly generated invalid RSA signatures.
Further debugging showed that P and Q didn't meet the rule P < Q (yielding invalid U).
RNP worked with such keys, and my guess is libgcrypt utilizes U in calculations, while OpenSSL doesn't.

While it's okay to behave incorrectly on an invalid secret key, confusing things here are:

  • import of invalid secret key without any warning
  • randomly erroring signing: it may happen on 2nd sign operation or succeed for 100 calls.

Sample secret key and some helper scripts attached.



Event Timeline

werner triaged this task as Normal priority.Oct 11 2021, 5:45 PM
werner edited projects, added Feature Request, gnupg (gpg23); removed Bug Report.
werner added a subscriber: werner.

OpenPGP requires the P < U property and gpg does also. In some parts of the GnuPG we re-calculate the CRT parameters but not in these code paths. Right, a better error message would be appropriate. I'll turn this into a feature request.

werner renamed this task from GnuPG randomly generates invalid RSA signatures if secret key has P > Q. to Issue better error message for invalid OpenPGP RSA keys.Oct 11 2021, 5:45 PM
werner added a project: OpenPGP.