Perl Crypt-Eksblowfish Cypher encrypted string and must be decrypted in python

Question

A Perl script use this module to encrypt string http://search.cpan.org/~zefram/Crypt-Eksblowfish-0.009/lib/Crypt/Eksblowfish.pm

I need to code the decrypt fonction in python . I know the key and the salt . I tried to use py-bcrypt but it seems that the two equiv function

$ciphertext = $cipher->encrypt($plaintext); $plaintext = $cipher->decrypt($ciphertext);

are not implemented .

How can i do ? Is there a python module anywhere that can help me to decrypt my strings ?

Figured out the last piece of the puzzle and updated my answer. — ErikR

ErikR ErikR · Accepted Answer · 2015-01-17T17:06:50

Update: The complete answer is the Perl code:

my $cipher = Crypt::EksBlowFish->new($cost, $salt, $key);

is equivalent to this Python code:

bf = Eksblowfish()
bf.expandkey(salt, key)
for i in xrange(cost << 1):
  bf.expandkey(0, key)
  bf.expandkey(0, salt)

See this repo for example code: https://github.com/erantapaa/python-bcrypt-tests

Original answer:

A partial answer...

I'm assuming you are calling this Perl code like this:

use Crypt::EksBlowfish;

my $cipher = Crypt::EksBlowFish->new($cost, $salt, $key);
$encoded = $cipher->encrypt("some plaintext");

The new method is implemented by the C function setup_eksblowfish_ks() in lib/Crypt/EksBlowfish.xs. This looks like it is the same as the expandKey method in the Python code (link)

The main difference is the $cost parameter which is not present in the Python method. In the Perl code the $cost parameter controls how many times this loop is executed after the key schedule has been set up:

    for(count = 1U << cost; count--; ) {
            for(j = 0; j != 2; j++) {
                    merge_key(j == 0 ? expanded_key : expanded_salt, ks);
                    munge_subkeys(ks);
            }
    }

The Perl ->encrypt() method enciphers a 64-bit word. The equivalent Python code is:

bf.cipher(xl, xr, bf.ENCRYPT)

where xl and xr are integers representing the left 32-bits and right 32-bits respectively.

So the recipe should go something like this:

Create the Python object: bf = EksBlowfish()
Initialize the key schedule: bf.expandkey(salt, key)
Further munge the key schedule using the cost parameter (TBD)
Encrypt with bf.cipher(xl, xr, bf.ENCRYPT)

Perl Crypt-Eksblowfish Cypher encrypted string and must be decrypted in python

1 Answers