Bilkent University
Department of Computer Engineering


Plaintext Recovery Attack Against RC4A


Mehmet Karahan

RC4 is one of the simplest stream cipher designed by Ronald Rivest in 1987. It is still used in varied industrial applications. RC4 consists of two main algorithms; the Key Scheduling Algorithm (KSA) which takes the secret key as input and produce initial state and the Pseudo-Random Generation Algorithm (PRGA)which takes initial state and produce keystream bytes.There are several analyses and attacks on these two algorithms separately. There are also analyses on RC4 as a black box that is the secret key as input and the keystream output words as output. In 2013, Alfardan et al. introduced ciphertext only plaintext recovery attacks against RC4 used by Transport Layer Security (TLS) protocol. They show that plaintext recovery for RC4 in TLS is possible for initial bytes of plaintext stream when it is provided that sufficiently many independent encryptions of the same plaintext are available. RC4A is one of the variants of RC4, which has been proposed in 2004, to remove some weaknesses of RC4. In the proposed thesis work, we intend to analyze RC4A stream cipher and apply ciphertext only plaintext recovery attacks against RC4A.


DATE: 24 November, 2014, Monday @ 15:40