Bug#885127: GnuTLS update breaks self-signed certificates

[Daniel Kahn Gillmor]

Control: tags 885127 + moreinfo unreproducible

On Fri 2017-12-29 14:38:14 +0200, Rémi Denis-Courmont wrote:
> The version of GnuTLS in Debian incorrectly flags self-signed certificates as 
> insecure certificate chain algorithm. This makes no sense; the flag is for 
> certificate chains using insecure algorithms such as MD2, MD5 and SHA-1.

sorry, i'm having a hard time seeing this.  In the example you give below:

> This is reproducible also with gnutls-bin (both with Debian and upstream 
> GnuTLS):
>
> # gnutls-cli self-signed.badssl.com
> Processed 148 CA certificate(s).
> Resolving 'self-signed.badssl.com:443'...
> Connecting to '104.154.89.105:443'...
> - Certificate type: X.509
> - Got a certificate list of 1 certificates.
> - Certificate[0] info:
>  - subject `CN=*.badssl.com,O=BadSSL,L=San Francisco,ST=California,C=US', 
> issuer `CN=*.badssl.com,O=BadSSL,L=San Francisco,ST=California,C=US', serial 
> 0x0086fb4dc8e5dd0f18, RSA key 2048 bits, signed using RSA-SHA256, activated 
> `2016-08-08 21:17:05 UTC', expires `2018-08-08 21:17:05 UTC', pin-
> sha256="9SLklscvzMYj8f+52lp5ze/hY0CFHyLSPQzSpYYIBm8="
>         Public Key ID:
>                 sha1:7965dfc93c6ae6fe8381ec482216ec44ef47282a
>                 sha256:f522e496c72fccc623f1ffb9da5a79cdefe16340851f22d23d0cd2a58608066f
>         Public Key PIN:
>                 pin-sha256:9SLklscvzMYj8f+52lp5ze/hY0CFHyLSPQzSpYYIBm8=
>         Public key's random art:
>                 +--[ RSA 2048]----+
>                 |                 |
>                 |     .           |
>                 |    o . .   o    |
>                 |     = o o o .o..|
>                 |    + + S o . .=.|
>                 | E . + o + o .. .|
>                 |  . . . + o  +o  |
>                 |         . .+. . |
>                 |            .o...|
>                 +-----------------+
>
> - Status: The certificate is NOT trusted. The certificate issuer is unknown. 
> The certificate chain uses insecure algorithm. 
> *** PKI verification of server certificate failed...
> *** Fatal error: Error in the certificate.
> *** handshake has failed: Error in the certificate.


the error says "The certificate issuer is unknown", which is surely the
*correct* response for a self-signed certificate when you haven't added
that certificate to your list of X.509 root authorities.

In the forwarded bug report
(https://gitlab.com/gnutls/gnutls/issues/347), Andreas says:

>>> a) gnutls-cli self-signed.badssl.com
>>> b) Generate a test-cert with "certtool --generate-self-signed " with
>>> default algoritms and use gnutls-serv/gnutls-cli

(though presumably not in that order)

well, i tried that, and things still worked for me.

in particular, to generate the self-signed certificate, i did:

   certtool --generate-privkey --outfile key.pem
   certtool --generate-self-signed --load-privkey key.pem --outfile cert.pem

when answering the questions in the second invocation, i just hit enter
on everything except:


Common name: bad.example
The certificate will expire in (days): 30
Is this a TLS web server certificate? (y/N): y
Will the certificate be used for encryption (RSA ciphersuites)? (Y/n): n

Once that was done, i pointed bad.example to 127.0.0.1 in /etc/hosts,
launched the server with:

   gnutls-serv --x509keyfile key.pem --x509certfile cert.pem

and then connected with the client like so:

   gnutls-cli --x509cafile cert.pem bad.example:5556


everything worked successfully.

Can you give a clearer example of the problem you're seeing?  I don't
see anything broken in my tests.

    --dkg
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