Thank you very much Dave, _Motty
On 10/31/2015 10:47 AM, Dave Platt wrote:
Thanks Jeff, just to confirm, password are not sent in plain text? I want to safeguard against man in the middle attacks, sniffing traffic of clients.That's correct. The way it works is: - Both the client, and Asterisk, know what the password is. - The client sends a SIP message which would require authorization (a register or invite, for example). It provides the username in the message. - The server generates a random "nonce" (basically a big random number) and sends it back to the client... basically saying "Use this nonce, and your password, to prove who you are." - The client combines the nonce, and the password, and uses the combined data as input into a hashing function (I can't recall whether MD-5, SHA-1, or something more modern is used). I *think* some of the other details of the original message are also included in the hash but don't recall for certain. - The client re-sends the original message, and includes its username, the nonce, and the hash. It does not send the password at all. - The server makes sure that the nonce is is the most recent one it sent, and that this is the first time the client has sent back that particular nonce. Once that's certain, the server uses the nonce and its copy of the password to compute the hash, and compares this with the hash the client sent. - If the hashes match, the server "knows" that the client knows the correct password (to a very high degree of certainty) and it allows the command to proceed. If they don't match, the client doesn't know the password, and the command is rejected. The hash functions that are used, are ones which would make it extremely difficult (months or years of computing time) to figure out what the password is, by breaking the hash algorithm. Of course, if a "weak" (short, guessable) password is used, it can be broken by a dictionary attack or brute force - the hash technique can't defend against this.
-- _____________________________________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- New to Asterisk? Join us for a live introductory webinar every Thurs: http://www.asterisk.org/hello asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
