crypt() isn't a full system for encrypting and decrypting data. It is a one way 'hash' used for encrypting passwords. The old system for unixish password protection used crypt().

The salt is a two character string that is "blended" into to given password when hashing to help confuse the reversing of hashes back to passwords. The stored password is of the form: SSHHHHHHHHHHH. When you are given a password and you want to check it against the stored hash, you simply do:

sub passtest {
  $passtotest=shift;
  $crypted=shift;
  return ( crypt($passtotest,$crypted) eq $crypted );
}
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The crypt function will just take the first two characters off of it's second argument and thus use the same salt as the originally crypted password. See perldoc -f crypt for more on this.

Just please don't think you can get data back out of crypt() =)

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                  Pronunciation: &-'solt
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                  Etymology: Middle English assaut, from Old French, from
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                  Date: 14th century
                  1 a : a violent physical or verbal attack b : a military attack
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