I'm trying to brute force a 3DES problem given a reduced keyspace (ie I know the first half of the key) but with an unknown IV. The code decrypts to plaintext. My first thought was that I could set the IV to the first 8 bytes of the CT, decode the rest and then substitute back to find the IV. This doesn't seem to work though - my brute forcer cannot find plaintext. I thought maybe it was getting confused with padding bytes at the end of the block being non-printable, so I removed the last 16 bytes as well, but that doesn't produce any results either.
Is there a flaw with my logic or is it more likely to be in my code?
Additional information from the comments
The ciphertext was generated using 3DES CBC and a 128 bit 3DES ABA key.
The key is 16 bytes, I know the first 10 (a ten letter word) and the next six are numbers (as in the ascii val of the digits 0-9). I'm basically brute forcing from WORDWORDWO000000 to WORDWORDWO999999.