[SSHD-330] Handshake fails (wrong shared secret) 1 out of 256 times

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.11.0
• Fix Version/s: 0.12.0
• Assignee: Guillaume Nodet
• Reporter: Pasi Eronen
• Created: 12/Jun/14 09:26
• Updated: 01/Apr/16 09:24
• Resolved: 16/Jun/14 07:31

Description

The shared secret returned by KeyAgreement.generateSecret() is a byte array, which can (by chance, roughly 1 out of 256 times) begin with zero byte. In SSH, the shared secret is an integer, so we need to strip the leading zero(es).

Some JCE providers might strip leading zeroes, though. SunJCE used to do this in Java 6, I think, but not anymore in Java 7 – and there was an almost identical bug (handshake fails 1 out of 256 times) in Java's SSL/TLS implementation in early Java 7 versions (see http://bugs.java.com/view_bug.do?bug_id=8014618).

Pull request here:
https://github.com/apache/mina-sshd/pull/5

How to reproduce with OpenSSH client (assuming Mina SSH server running in port 9922):

for x in

{1..500}; do sshpass -p wrong ssh -p9922 -oKexAlgorithms=diffie-hellman-group-exchange-sha1 someuser@localhost; done

for x in {1..500}

; do sshpass -p wrong ssh -p9922 -oKexAlgorithms=ecdh-sha2-nistp256 someuser@localhost; done

Issue Links

• depends upon: SSHD-356 Backport SSHD-330 Handshake fails (wrong shared secret) to 0.9 release
• relates to: SSHD-346 "key_verify failed for server_host_key" Error