RC4¶

Basic Introduction¶

RC4 was designed by Ron Rivest and originally belonged to RSA Security as a proprietary cryptographic product. It is a byte-oriented stream cipher with a variable key length that is very simple yet very effective. The RC4 algorithm is widely used in SSL/TLS protocols and WEP/WPA protocols.

Basic Process¶

RC4 mainly consists of three processes:

• Initialize S and T arrays.
• Initialize permutation S.
• Generate stream key.

Initialize S and T Arrays¶

The code for initializing S and T is as follows:

for i = 0 to 255 do
    S[i] = i
    T[i] = K[i mod keylen]

Initialize Permutation S¶

j = 0
for i = 0 to 255 do 
    j = (j + S[i] + T[i]) (mod 256) 
    swap (S[i], S[j])

Generate Stream Key¶

i = j = 0 
for each message byte b
    i = (i + 1) (mod 256)
    j = (j + S[i]) (mod 256)
    swap(S[i], S[j])
    t = (S[i] + S[j]) (mod 256) 
    print S[t]

The first two parts are generally called KSA (Key Scheduling Algorithm), and the last part is PRGA (Pseudo-Random Generation Algorithm).

Attack Methods¶

To be supplemented.