Why is a SHA-1 Hash 40 characters long if it is only 160 bit?

Question

The title of the question says it all. I have been researching SHA-1 and most places I see it being 40 Hex Characters long which to me is 640bit. Could it not be represented

Answer 1

I think the OP's confusion comes from a string representing a SHA1 hash takes 40 bytes (at least if you are using ASCII), which equals 320 bits (not 640 bits).

The reason is that the hash is in binary and the hex string is just an encoding of that. So if you were to use a more efficient encoding (or no encoding at all), you could take only 160 bits of space (20 bytes), but the problem with that is it won't be binary safe.

You could use base64 though, in which case you'd need about 27-28 bytes (or characters) instead of 40 (see this page).