![]() ![]() ![]() Here the issue is not cipher mis-matches - but use of an archaic PKI pair - based on DSA. On my server I have an 'old' client and the 'latest' client installed - and get different behavior connecting to a server. (chosen_kex = NULL, chosen_host_key = ssh-rsa)ĭebug: Ssh2Common: DISCONNECT received: Algorithm negotiation failed.Įdit: added 0 New Section - what about keys that stop working? ![]() server list : Ssh2Transport: lang s to c: `', lang c to s: `'ĭebug: Ssh2Transport: Couldn't agree on kex or hostkey alg. server list : Ssh2Transport: Algorithm negotiation failed for s_to_c_cipher: client list: aes128-cbc,3des-cbc,twofish128-cbc,cast128-cbc,twofish-cbc,blowfish-cbc,aes192-cbc,aes256-cbc,twofish192-cbc,twofish256-cbc,arcfour vs. debug: OpenSSH: Major: 7 Minor: 3 Revision: 0ĭebug: Ssh2Transport: All versions of OpenSSH handle kex guesses incorrectly.ĭebug: Ssh2Transport: Algorithm negotiation failed for c_to_s_cipher: client list: aes128-cbc,3des-cbc,twofish128-cbc,cast128-cbc,twofish-cbc,blowfish-cbc,aes192-cbc,aes256-cbc,twofish192-cbc,twofish256-cbc,arcfour vs. supported (OpenSSH should have the option -Q) just start a connection to yourself, e.g., ssh -v localhost and there are lines such as this to tell you wat is known: debug1: SSH2_MSG_KEXINIT sentĭebug2: kex_parse_kexinit: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-grousha1,diffie-hellman-group1-sha1ĭebug2: kex_parse_kexinit: kex_parse_kexinit: what was found (and used): debug2: mac_setup: found hmac-sha1ĭebug1: kex: server->client aes128-ctr hmac-sha1 noneĭebug1: kex: client->server aes128-ctr hmac-sha1 noneĮxtra: debug info from a failed connect - more details If you client does not have an option to provide the keys, etc. ![]() Looking above you can see it does not support any of the - 15 years later - preferred algorithms, not even one -cbr (rotating), only -cbc (block-copy). Mine - was - an very old client - for my desktop. Product: SSH Secure Shell for Workstations Macs hmac-sha2-256,hmac-sha2-512,hmac-sha1-96,hmac-sha1Īn easy way to see what ciphers you current client supports (assuming CLI) is ssh -h and see if that provides something like: Supported MAC useful command is: ssh -V ssh2: SSH Secure Shell 3.2.9 Windows Client # consider removing hmac-sha1-96,hmac-sha1,hmac-md5 "Soon!" KexAlgorithms MAC message authentification code # and this should be deleted ASAP as it is clearly "one of the problems" with SSL based encryption # only adding diffie-hellman-group-sha1 as an "old" KEX # an older kex are: none,KexAlgorithms diffie-hellman-group1-sha1 # only adding aes256-cbc as an "old" cipher # ciphers aes128-cbc,aes192-cbc,aes256-cbc,blowfish-cbc,arcfour # older clients may need an older cipher, e.g. # The dafaults starting with OpenSSH 6.7 are: The key lines to change/add in sshd_config being: ciphers hmac-sha2-256,hmac-sha2-512,hmac-sha1-96,hmac-sha1 Server solution: bring back "old" settings so "old" clients can continue to connect that is, - friendly to existing clients - edit the sshd_config file and add back (enough) of the old ciphers. Two solution paths: fix/patch the server or - fix/patch the client. My problem is I have an old client that does not have any of the new defaults, so it cannot connect. The full set of algorithms remains available if configuredĮxplicitly via the Ciphers and MACs sshd_config options. Sshd(8): The default set of ciphers and MACs has been altered to Turns out the new version was not broken - but OpenBSD/OpenSSH starting changing the key exchange defaults starting with OpenSSH-6.7p1 see:, noteably: Changes since OpenSSH 6.6 There is a massive hint - that I did not notice when this first happened to me (using the GUI interface, and I just clicked it away and 'was angry' with 'stupid update - new version is broken'. This can 'break' things that are, read were, working well. OpenBSD (who maintain/develop OpenSSH) have a policy of OpenBSD to not be concerned about backwards compatibility. With OpenSSH - defaults change frequently. After an update - side-effects may come into play. ![]()
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