[106393] in cryptography@c2.net mail archive
Password vs data entropy
daemon@ATHENA.MIT.EDU (Alex Pankratov)
Fri Oct 26 09:57:51 2007
From: "Alex Pankratov" <ap@poneyhot.org>
To: <cryptography@metzdowd.com>
Date: Thu, 25 Oct 2007 21:16:21 -0700
Say, we have a random value of 4 kilobits that someone wants
to keep secret by the means of protecting it with a password.
Empirical entropy estimate for an English text is 1.3 bits of
randomness per character, IIRC.
Assuming the password is an English word or a phrase, and the
secret is truly random, does it mean that the password needs
to be 3100+ characters in size in order to provide a "proper"
degree of protection to the value ?
Or, rephrasing, what should the entropy of the password be
compared to the entropy of the value being protected (under
whatever keying/encryption scheme) ?
I realize that this is rather .. err .. open-ended question,
and it depends on what one means by "protected", but I'm sure
you can see the gist of the question. How would one deem a
password random enough to be fit for protecting an equivalent
of N bits of random data ? Is it a 1-to-1 ratio ?
Thanks,
Alex
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