Re: Ref:Using NSE OpenSSL for Blowfish?

[Ron <ron () skullsecurity net>]

Omar Herrera wrote:
> Hi Ron,
>
> I'm not familiar with NSE's OpenSSL module, but i think I know what
> might be causing the problem: the Initialization Vector.
>
> I couldn't find in the module's documentation the encryption mode used,
> but I'm assuming its CBC. Blowfish does operate on 64 bit blocks, but in
> CBC mode the result of encrypting each block is also used to modify the
> encryption process of the next block. That is why you can't decipher
> blocks independently unless you use ECB mode.
>
> Obviously the first block doesn't have any previous information from
> other blocks, and here is where the IV is used; this IV serves as a
> mechanism to add randomness to the encryption process of the first block.
>
> Now, you must make sure you are using exactly the same mechanisms to
> generate the IV for the encryption and the decryption. For instance,
> within Openssl if you use a password the key and the IV will be
> generated from the password using a PKCS5 compatible protocol
> (http://www.openssl.org/docs/crypto/EVP_BytesToKey.html), so the IV
> won't be empty.
>
> Within the NSE module it is not clear to me what will be passed to the
> openssl functions (i.e. will it be a null pointer or random data).
> OpenSSL encryption tool requires that you pass an IV whenever you use
> only an hexadecimal key (see -K and -iv in
> http://www.openssl.org/docs/apps/enc.html); the same with the encryption
> functions of the OpenSSL library (see
> http://www.openssl.org/docs/crypto/blowfish.html), since all encryption
> modes different than ECB require an IV)
>
> Salting is not used by default and doesn't seem to be included as an
> option in the NSE module, so it is less likely that this is your problem.
>
> The best way to make sure is to encrypt your string with the NSE module
> using a key and an IV of your choice, and then trying to decrypt it also
> with the NSE functions. Next, I would suggest to encrypt your text with
> the openssl command line tool (using the same keys and IV) and decrypt
> it using the NSE module, and viceversa. Since salts are apparently not
> being used, you should get exactly the same result.
>
> If this works, then this would confirm that the undefined IV in NSE is
> the problem.
>
> I hope this helps,
>
> Omar Herrera

Hi Omar,

That's incredibly helpful, thanks! I gave up working on this for today
(too tired/frustrated to be productive).

A question, though: the IV you're talking about, is that also the key?
Or is there a separate key and IV? The data I'm using is encrypted in C,
and the interface looks like this:
--
void Blowfish_Init(BLOWFISH_CTX *ctx, unsigned char *key, int keyLen);
void Blowfish_Encrypt(BLOWFISH_CTX *ctx, unsigned long *xl, unsigned
long *xr);
void Blowfish_Decrypt(BLOWFISH_CTX *ctx, unsigned long *xl, unsigned
long *xr);
--

So I only see a key, unless the IV is hardcoded into the library.

In either case, I don't think I'm decrypting the data in the same order
as it's encrypted, so I'd bet that's the problem.

Thanks!
Ron

-- 
Ron Bowes
http://www.skullsecurity.org/

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