Twenty Year Anniversary

jBCrypt Entropy Reduction

jBCrypt Entropy Reduction
Posted Feb 2, 2010
Authored by Damien Miller

jBCrypt versions prior to 0.3 suffered from a bug related to character encoding that substantially reduced the entropy of hashed passwords containing non US-ASCII characters.

tags | advisory
MD5 | d7a5b239702b98ba4f71ff8bbcdc491a

jBCrypt Entropy Reduction

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jBCrypt security advisory
=========================

jBCrypt is a Java implementation of OpenBSD's Blowfish password hashing
algorithm, as described in "A Future-Adaptable Password Scheme" by Niels
Provos and David Mazieres (USENIX, 1999).

Versions of jBCrypt before 0.3 suffered from a bug related to character
encoding that substantially reduced the entropy of hashed passwords
containing non US-ASCII characters. An incorrect encoding step
transparently replaced such characters by '?' prior to hashing. In the
worst case of a password consisting solely of non-US-ASCII characters,
this would cause its hash to be equivalent to all other such passwords
of the same length.

jBCrypt-0.3, available from http://www.mindrot.org/projects/jBCrypt/
fixes this bug. Please note that passwords containing international
characters that were hashed using a previous version of jBCrypt will
not verify using jBCrypt-0.3. This may necessitate re-hashing of such
passwords.

This bug was responsibly disclosed by Aliaksandr Radzivanovich.


Damien Miller <djm@mindrot.org>
February 1, 2010


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