Cringely Gives KnowNow Some Unbelievable Free Press... (fwd)

[Enzo Michelangeli]

From: "Ben Laurie" <ben at algroup.co.uk>

> BTW, I don't see why using a passphrase to a key makes you vulnerable to
> a dictionary attack (like, you really are going to have a dictionary of
> all possible 1024 bit keys crossed with all the possible passphrases?
> Sure!).

At least in OpenPGP, the correctness of the passphrase can be checked just
by verifying a CRC, without any PK operation. Quoting RFC2440:

 5.5.3. Secret Key Packet Formats
   [...]
   The 16-bit checksum that follows the algorithm-specific portion is
   the algebraic sum, mod 65536, of the plaintext of all the algorithm-
   specific octets (including MPI prefix and data).  With V3 keys, the
   checksum is stored in the clear.  With V4 keys, the checksum is
   encrypted like the algorithm-specific data. This value is used to
   check that the passphrase was correct.

(OK, that weakness can't be ascribed to RSA, but it's there.)

Enzo







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