blowfish keysize

Anon

Hi,

Is there a way to set the keysize for blowfish encryption? I'm using mcrypt 2.4, and when encrypting with another keysize then 56, I get:

Warning: key size incorrect; supplied length: 55, needed: 56 in /tmp/phptemp on line 8

Blowfish allows other keysizes, but how do I specify it?

Code is ($key is 55 chars long):

$key = "nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn";
$value = "secret";

$td = mcrypt_module_open (MCRYPT_BLOWFISH, "", MCRYPT_MODE_CFB, "");
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size ($td), MCRYPT_RAND);
mcrypt_generic_init ($td, $key, $iv);
$encrypted_data = mcrypt_generic ($td, $value);
mcrypt_generic_end ($td);
echo $encrypted_data;

kparker

I don't see where you can, with the php interface to mycrypt. Perhaps you could just append one extra char to the key?

roel_v

Thanks, but I want a variable key length, so that we can have a random length password.
I largely solved it though: looks like mcrypt_generic_init() always prints out this if you don't use the maximum key length that the cypher allows; you can however use the shorter key. imho this is not a good error message, but maybe I'm wrong. I solved it by putting a @ in front of the function call :-)

kparker

OK, but what does key length have to do with random password lengths?

roel_v

Ah yes it's indeed a bit confusing, we have a whole system where the blowfish key is deduced from a password, the key size has to stay the same but the password size is variable... I had to be compatible with an old perl program that used a 32 byte key, but that requirement is cancelled in the mean time so now I just use a 56 byte key. Thanks anyway for your concern :-)