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ntbtls: use of shorter hash for ECC
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Description

Need to check the TLS protocol spec., but it seems that rejecting shorter hash algo for ECC may be wrong.

The point in question is:

diff --git a/src/pkglue.c b/src/pkglue.c
index af8cf92..44de028 100644
--- a/src/pkglue.c
+++ b/src/pkglue.c
@@ -152,8 +152,10 @@ _ntbtls_pk_verify (x509_cert_t chain, pk_algo_t pk_alg, md_algo_t md_alg,
           {
             debug_msg (1, "a %u bit hash is not valid for a %u bit ECC key",
                        (unsigned int)hashlen*8, qbits);
+#if 0
             err = gpg_error (GPG_ERR_DIGEST_ALGO);
             goto leave;
+#endif
           }
 
         if (hashlen > qbits/8)

I ran the command ntbtls-cli --debug 999 dev.gnupg.org which has ECDSA key with NIST P-384, and it fails without the change above.

Revisions and Commits

rT Not Too Bad TLS
rT5d3d9d9904d2 Allow server's use of SHA256 hash with secpr384 key.

Related Objects

Event Timeline

• gniibe triaged this task as Normal priority.Jul 6 2022, 6:57 AM
• gniibe created this task.
• gniibe added a comment.Jul 8 2022, 2:30 AM

There is a description: https://datatracker.ietf.org/doc/html/rfc8422#section-5.10

It seems that it's OK to use SHA256 for ECDSA with secpr384 (as dev.gnupg.org does).

So, I'm going to remove the restriction from NtbTLS.

• gniibe added a project: Restricted Project.Jul 8 2022, 9:53 AM

Pushed the change.

• gniibe added a commit: rT5d3d9d9904d2: Allow server's use of SHA256 hash with secpr384 key..Jul 8 2022, 10:49 AM
• werner changed the task status from Open to Testing.Sep 22 2022, 10:53 AM
• werner removed a project: Restricted Project.
• werner added a project: Restricted Project.Sep 18 2023, 4:03 PM
• werner added a subscriber: • werner.

Well, even out new versions.gnupg.org uses a shorter hash. Better get that released asap.

• werner moved this task from Restricted Project Column to Restricted Project Column on the Restricted Project board.Sep 18 2023, 4:03 PM
aheinecke added a project: vsd32.Nov 15 2023, 9:46 AM
aheinecke added a subscriber: aheinecke.

So the last thing to do here would be an NTBTLS release? Then we should make sure not to forget to do that?

• werner edited projects, added Feature Request; removed vsd32.Jan 8 2024, 2:01 PM

Yeah we should do an ntbtls release. As a core library it does no matter much which workboard we use. Let's remove it the vsd tag.

• werner moved this task from Backlog to WIP on the ntbtls board.Jan 8 2024, 2:04 PM
• werner mentioned this in T6925: Release ntbtls 0.3.2.Jan 12 2024, 7:45 AM
• gniibe closed this task as Resolved.Jan 26 2024, 1:04 AM

Fixed in 0.3.2.