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salt-cryptographycrypt

salt two-character string 12 bits

Hi everyone my question as dumb as it seems is the following:
Using the man crypt()
salt is a two-character string chosen from the set [a–zA–Z0–9./] and it's a 12 bits how is that since it's a two-character string it should be a 16 bits hence a char size is a byte ??

Solution

  • If you count total number of characters in the set you'll see there are 64 (2^6) elements: 26 latin uppercase letters, 26 lowercase, 10 digits plus 2 extra characters: period and slash.

    Two 6-bit characters -- 12 bits.

    Evidently, crypt() must be mapping salt characters to bit sequences using something-else-than-ASCII (for user convenience, I suspect).