On Wed, 6 Feb 2002, -l0rt- wrote: > When using password auth, how difficult would it be for someone > to sniff my connection and extract/crack my password? I only ask > because someone mentioned that it would not be too difficult. What > are the primary differences between password auth and pubkey? Is using > password auth really that much less secure? Please give me the > details.. i covered these topics in a recent linux journal piece i wrote: http://www.linuxjournal.com/article.php?sid=5672 briefly: o password recovery from password authentication http://www.openwall.com/advisories/OW-003-ssh-traffic-analysis.txt in a nutshell, the exact length of the password used in SSH-1.5 (protocol) can be observed by an eavesdropper. then, using a password cracker, they can improve tehir efficiency and speed things up by a factor of 50 at the outside. note that this isn't terribly huge if you have a strong password, but it can be noticable. secondly, this doesn't affect SSH-2 (the protocol). o differences between password and public key auth ssh can use DSA or RSA keys for authentication. the client sends, rather than a password, a reply encrypted with your private key, which your public key (which the server has been told about by you) can decrypt. you are now verified, as only your key could have done that. these keys are protected on your system, typically, by using a passphrase. a great discussion of how to do this is: http://www-106.ibm.com/developerworks/library/l-keyc.html to compare these two methods of authentication, password and public key, is pretty simple in many respects. first, the search space for passwords is significantly smaller than that for ssh RSA/DSA keypairs. secondly, you can protect your ssh identity with longer passphrases, which are typically stronger, all things being equal. the risk here is a compromise of your host to capture the key (either an unprotected key or a capture of your passphrase or a capture of the stored key in your agent). good host security will help protect against this. in a nutshell, look at public key authentication using SSH-2 (not SSH-1.5), as i discuss in my LJ piece (where i looked at the attacks in the year 2001 against the ssh toolset and make some reccomendations), written to answer these kinds of questions. all the best, ____________________________ jose nazario joseat_private PGP: 89 B0 81 DA 5B FD 7E 00 99 C3 B2 CD 48 A0 07 80 PGP key ID 0xFD37F4E5 (pgp.mit.edu)
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