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Bug 1238333 - GnuTLS does not interoperate with OpenSSL and NSS in TLS1.1 and 2048 bit DSA keys
Summary: GnuTLS does not interoperate with OpenSSL and NSS in TLS1.1 and 2048 bit DSA ...
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: gnutls
Version: 7.1
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Nikos Mavrogiannopoulos
QA Contact: BaseOS QE Security Team
URL:
Whiteboard:
: 1418018 (view as bug list)
Depends On:
Blocks: 1218420
TreeView+ depends on / blocked
 
Reported: 2015-07-01 15:40 UTC by Hubert Kario
Modified: 2017-02-21 16:34 UTC (History)
6 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2015-10-22 09:09:16 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)
DSA certificates for reproducer (37.97 KB, application/x-gzip)
2015-07-01 15:40 UTC, Hubert Kario 		no flags Details
View All

Description Hubert Kario 2015-07-01 15:40:07 UTC 
Created attachment 1045132 [details]
DSA certificates for reproducer

Description of problem:
When the clients and servers use 2048 or 3072 bit DSA certificates with GnuTLS and TLS1.1, the connection is rejected.

Version-Release number of selected component (if applicable):
nss-3.19.1-5.el7_1.x86_64
gnutls-3.3.8-12.el7.x86_64
openssl-1.0.1e-42.el7_1.6.x86_64

How reproducible:
Always

Steps to Reproduce:
1. tar xzf ~/dsa-certificates.tar.gz
2. cd dsa-certificates/
3. Pick a server and a client, start them:

# openssl server
openssl s_server -key dsa-server/key.pem -cert dsa-server/cert.pem -CAfile <(cat ca/cert.pem dsa-ca/cert.pem) -cipher EDH-DSS-DES-CBC3-SHA -Verify 1

# NSS server
/usr/lib64/nss/unsupported-tools/selfserv -d sql:./nssdb/ -p 4433 -V tls1.0: -c :0013 -H 1 -rr -S dsa-server

# GnuTLS server
gnutls-serv --http -p 4433 --x509keyfile dsa-server/key.pem --x509certfile <(cat dsa-server/cert.pem dsa-ca/cert.pem) --x509cafile <(cat ca/cert.pem dsa-ca/cert.pem) --require-client-cert --verify-client-cert

# openssl client
openssl s_client -CAfile ca/cert.pem -cipher EDH-DSS-DES-CBC3-SHA -connect localhost:4433 -cert dsa-client/cert.pem -key dsa-client/key.pem -tls1_1

# NSS client
/usr/lib64/nss/unsupported-tools/tstclnt -h localhost -p 4433 -d sql:./nsscl/ -c :0013 -V tls1.0:tls1.1 -n dsa-client

# GnuTLS client
gnutls-cli --x509cafile ca/cert.pem --x509keyfile dsa-client/key.pem --x509certfile dsa-client/cert.pem --priority NORMAL:-VERS-TLS1.2 -p 4433 localhost

Actual results:
Connections between GnuTLS and any other implementation fail, connections between NSS and OpenSSL work.

Expected results:
All combinations should work

Additional info:
When used with 1024 bit DSA certificates, the connections work as expected.

While the bug is filed for GnuTLS, I'm not sure if this is actually GnuTLS fault, but since OpenSSL and NSS do interoperate with each other, other implementations will likely aim for same behaviour...
Comment 3 Nikos Mavrogiannopoulos 2015-07-02 10:40:17 UTC 
That non-interoperation is intentional. According to DSS standard you cannot use 2048+ bit keys with SHA1, and given that TLS 1.1 only uses SHA1 it cannot be used with those keys.

That's the reason gnutls doesn't interoperate. It refuses to violate the DSS standard. I have described that in a TLS profile (not adopted by the TLS WG):
https://tools.ietf.org/html/draft-mavrogiannopoulos-tls-dss-01

So I believe the bug should be reported against openssl and NSS which violate DSS.
Comment 4 Nikos Mavrogiannopoulos 2015-07-02 10:41:05 UTC 
(to clarify the above message, the SHA1 with DSS refers to the ServerKeyExchange signature)
Comment 5 Tomas Mraz 2015-07-02 11:04:24 UTC 
I agree with Nikos here, that the fix should be in NSS and OpenSSL if anywhere. We should simply declare the DSS support in TLS for keys >= 2048bits as experimental and non-interoperable due to missing standards.

The DSS should be considered a legacy anyway and it does not make sense to spend too many resources on it.
Comment 6 Hubert Kario 2015-07-03 10:48:03 UTC 
(In reply to Tomas Mraz from comment #5)
> I agree with Nikos here, that the fix should be in NSS and OpenSSL if
> anywhere. We should simply declare the DSS support in TLS for keys >=
> 2048bits as experimental and non-interoperable due to missing standards.
> 
> The DSS should be considered a legacy anyway and it does not make sense to
> spend too many resources on it.

It's only the TLS 1.0 and TLS 1.1 with >= 2048 bit DSA that is lacking standards.

TLS 1.2 has provisions for DSA keys of this size and FIPS requirements can be easily met there.
(e.g DSA is listed as /the/ reason why the signature algorithms and hash algorithms are listed in pairs, not as two separate lists in Signature Algorithms extension)

So, yes, I agree that we should declare very specific combinations as unsupported (>= 2048 DSA with TLS 1.1), even if they appear to sometimes work (but violate standards). And then declare some combinations as experimental (any DSA with TLS 1.2).
Comment 7 Hubert Kario 2017-02-21 16:34:37 UTC 
*** Bug 1418018 has been marked as a duplicate of this bug. ***
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