06-23-2017, 03:48 AM
You don't have enough information to be able to recover a key.
Put simply, if you only know the first three bytes of the ciphertext, then that leaves 5 bytes unknown, which leaves up to (2^40) = 1,099,511,627,776 possible combinations.
In the example in the first post, there are 8 hex chars missing, which gives 16 bits of unknown information, or (2^32) potential candidates which equals 4,294,967,296 possibilities.
Put simply, if you only know the first three bytes of the ciphertext, then that leaves 5 bytes unknown, which leaves up to (2^40) = 1,099,511,627,776 possible combinations.
In the example in the first post, there are 8 hex chars missing, which gives 16 bits of unknown information, or (2^32) potential candidates which equals 4,294,967,296 possibilities.