[gnutls-help] Incompability between gnutls 3.5.8 and 3.6.5 for gnutls_encode_rs_value and gnutls_decode_rs_value

[Nicolas Mora]

Hello,

Last year I asked a question about encoding and decoding messages with 
ECDSA using GnuTLS. At that time, the functions to achieve this were 
present but not exported in GnuTLS 3.5.8. So the solution was to 
manually export them in my code [1] and it works like a charm for this 
version of GnuTLS [2].
Unfortunately, it seems that my code no longer works with GnuTLS 3.6.

I realized this by building and testing libjwt with gnutls backend under 
a Debian Stretch (GnuTLS 3.5.8), and a Debian testing (currently GnuTLS 
3.6.5).

My question is: Are there differences between GnuTLS 3.5.x and 3.6.x on 
the functions gnutls_encode_rs_value and gnutls_decode_rs_value or in 
the ECDSA encoding/decoding?

And if so, Are there a way to fix my code in order to encode and decode 
messages with ECDSA algorithm?

Thanks in advance for the help.

[1] - https://lists.gnupg.org/pipermail/gnutls-help/2017-May/004314.html
[2] - 
https://github.com/benmcollins/libjwt/blob/master/libjwt/jwt-gnutls.c#L25