Proving TLS-attack related open biases of RC4

Abstract

After a series of results on RC4 cryptanalysis in flagship cryptology conferences and journals, one of the most significant recent attacks on the cipher has been the discovery of vulnerabilities in the SSL/TLS protocol, by AlFardan et al. (USENIX 2013). Through extensive computations, they identified some new significant short-term single-byte biases in RC4 keystream sequence, and utilized those, along-with existing biases, towards the TLS attack. The current article proves these new and unproved biases in RC4, and in the process discovers intricate non-randomness within the cipher. In this connection, we also prove the anomaly in the 128th element of the permutation after the key scheduling algorithm. Finally, the proof for the extended key-length dependent biases in RC4 keystream sequence, a problem attempted and partially solved by Isobe et al. in FSE 2013, has also been completed in this work.