Known plaintext attack is a scenario in which the attacker has access to pairs of known plaintexts and their corresponding ciphertexts. This attack is considered to be highly practical, especially if the amount of pairs N is not too large. This attack scenario is more practical than the chosen plaintext attack. Probable word method which is a popular technique for solving classical simple substitution or transposition ciphers is an example of a known-plaintext attack.
Another example is the cryptanalysis of the German Enigma cipher using the so called bombs. It relied heavily on properly guessed opening words of the cryptograms (which were at the time called cribs). One of the most popular cribs was “Nothing to report”. In modern cryptography linear cryptanalysis is a typical example of a known plaintext attack.
OBAKE-512 uses procedures that avoid such attacks since the results are aleatory and different, even using the same data and key.
The data below represents the encryption of a text file with "PRIVACY AS IT SHOULD BE", using the OBAKE-512 algorithm with secret key "a", without any additional mechanism as COMPRESSION or COLUMNAR-TRANSPOSE. Note that the two initial bytes are related to the OBAKE HEADER and are present in every encrypted file whether using the OBAKE-512 algorithm.
If wished, you can download these files (which allows you to decrypt this information in your OBAKE application) making sure of our assertion.
Using the NPCR comparison among them, we got a top rate: every single byte is different from any other in any file. But, notice that it can sometimes vary since OBAKE-512 utilizes random schemes to avoid repetition in the same file/data but, precisely due to this, it can create some similarities between a single byte and position among files.
Bibliographic references
A. Biryukov et al., "Encyclopedia of Cryptography and Security", H. C. A. v. Tilborg Ed., SpringerScience+Business Media LLC, 2011.
Deavours, C.A. and L. Kruh, "Machine Cryptography and Modern Cryptanalysis", Artech House Ed., Boston, 1985
D. R.Stinson, "Cryptography - Theory and Practice", Ontario: Chapman & Hall/CRC, 2006.
