Circa 2005-04-20 dixit Jim C. Nasby:
: Actually, it's not as silly as you think. You can download rainbow
: tables for Windows/LanMan passwords up to 14 or 15 characters in length.
: Given the password hash and some code, you can determine the user's
: password in a matter of minutes.
I thought the idea of the salt was to aid in expanding the keyspace.
Even though the salt is known (in traditional Unix
passwd/shadow/master.passwd databases, it's stored at the beginning of
the password field), appending the salt to the password expands the
keyspace to length(password) + length(salt). With a (barely) reasonable
8-byte password and an 8-byte salt, that gives you a 128-bit key (if you
use password+salt as the key). Remember that the keyspace for a 16-byte
password is (theoretically) 256 times as large as the keyspace for a
15-byte password. If you require 10- or 12-byte passwords and add 12
bytes of salt, you approach 192-bit keys and get a keyspace between
10^14 and 10^21 times as large as 15-byte passwords (assuming your
password hash algorithm can handle 192-bit keys). Even a 160-bit key
(20 bytes = 10-byte password + 10-byte salt) has a formidable keyspace,
for now, assuming high-quality keys: 10^48 keys * 20 bytes is a lot of
storage space.
: Simply put, MD5 is no longer strong enough for protecting secrets. It's
: just too easy to brute-force. SHA1 is ok for now, but it's days are
: numbered as well. I think it would be good to alter SHA1 (or something
: stronger) as an alternative to MD5[...].
"Something stronger" being bcrypt-2a, based on Blowfish. Solar
Designer's public domain implementation is here:
http://www.openwall.com/crypt/
--
jim knoble | jmknoble@pobox.com | http://www.pobox.com/~jmknoble/
(GnuPG fingerprint: 809F:09B9:9686:D035:4AB0::9455:124B:0A62:DD6A:76D6)
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