How to decrypt unsalted openssl compatible blowfish CBC/PKCS5Padding password in python?

Question

I've been looking for a python library to help decrypt an openssl blowfish encrypted password.

I have managed to achieve this in Java but the python libraries to support this appeared more of a learning curve, and required rolling your own.

In terms of what we need to achieve, the password is unsalted and uses a passphrase, for the purposes of this question I've set this to "AAAAAAAA". The Cipher is "Blowfish/CBC/PKCS5Padding". The encrypted text will be read in as a string, same as the key and iv.

In openssl, this is 'simply':

~$ # This is encrypting
~$ echo -n 'password' | openssl enc -bf -nosalt -a -K AAAAAAAA -iv AAAAAAAA
eAIUXziwB8QbBexkiIDR3A==
~$ # This is reversing the encryption
~$ echo 'eAIUXziwB8QbBexkiIDR3A==' | openssl enc -d -bf -nosalt -a -K AAAAAAAA -iv AAAAAAAA
password

In java, the descryption is along the lines of:

private static final String KEY = "AAAAAAAA000000000000000000000000";
private static final String IV = "AAAAAAAA00000000";
private static final String FCN = "Blowfish/CBC/PKCS5Padding";
private static final String CN = "Blowfish";

final byte[] encoded = Base64.decode("eAIUXziwB8QbBexkiIDR3A==");
final SecretKeySpec key =
new SecretKeySpec(Hex.decodeHex(KEY.toCharArray()), CN);
final Cipher cipher = Cipher.getInstance(FCN, JCE_PROVIDER);
cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(Hex.decodeHex(IV.toCharArray())));
final byte[] decrypted = cipher.doFinal(encoded);
return new String(decrypted);

Can someone provide some guidance for python?

Roland Smith Roland Smith · Accepted Answer · 2012-09-01T13:20:41

Decoding hexadecimal and base64 encoded strings is built-in:

In [1]: "AAAAAAAA000000000000000000000000".decode('hex')
Out[1]: '\xaa\xaa\xaa\xaa\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

In [2]: "eAIUXziwB8QbBexkiIDR3A==".decode('base64')
Out[2]: 'x\x02\x14_8\xb0\x07\xc4\x1b\x05\xecd\x88\x80\xd1\xdc'

The PyCrypto library handles BlowFish (among others).

In [1]: from Crypto.Cipher import Blowfish

In [2]: KEY = "AAAAAAAA000000000000000000000000".decode('hex')

In [3]: IV = "AAAAAAAA00000000".decode('hex')

In [4]: cipher = Blowfish.new(KEY, Blowfish.MODE_CBC, IV)

In [5]: ciphertext = "eAIUXziwB8QbBexkiIDR3A==".decode('base64')

In [6]: cipher.decrypt(ciphertext)
Out[6]: 'password\x08\x08\x08\x08\x08\x08\x08\x08'

If you want to strip off the padding from the plaintext in one go:

In [14]: cipher.decrypt(ciphertext).replace('\x08', '')
Out[14]: 'password'

How to decrypt unsalted openssl compatible blowfish CBC/PKCS5Padding password in python?

1 Answers