Peter wrote: > Note that I am not a security expert. But you sure do a fine job of playing one on Linux-il, while trying to contradict people who make a living from being security experts, such as Aviram and myself. >> How is hash a digital signature? > > A hash is a checksum that has the property of being hard to duplicate > with a different data set (as in, message). A, mostly correct explanation of what a hash is snipped. > For a message, if a hash sum is computed and stored somewhere (perhaps > in the message itself, .. > then the content of the message cannot be tampered with without > changing the sum. But if the sum is part of the message, and I can tamper with the message, the only conclusion is that I can also tamper with the sum.
In other words, if you receive a message that has a SHA-1 of it in it, the only thing you can deduct is that whoever wrote this message (or someone in between) knows how to apply SHA-1 to it. It does not tell you that the person who wrote this message is the person written in the "From:" address, which means that for all intent and purposes, the message is not signed. A cryptographic hash is an irreversible function that can be applied the right way by anyone and the wrong way by no one. That's what makes it useful. A signing algorithm (at least, a public key signing algorithm) is a function that can be applied in one way only by someone who knows a secret part of a key, and the other way by anyone who knows the public part of the same key. Also, the public and private part must be tied by a 1:1 relationship. Shachar -- Shachar Shemesh Lingnu Open Source Consulting ltd. Have you backed up today's work? http://www.lingnu.com/backup.html ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
