SHA1 is a cryptographic function that takes as input a 2^64 bits maximum length message, and outputs a 160 bits hash, 40 caracters. SHA1 is an improvement of Sha-0, it was created by the NSA, and improve cryptographic security by increasing the number of operations before a collision (theory says 2^63 operations), however SHA1 is not considered as secure because 2^63 could be reach pretty easily.
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