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RC4

basic introduction

Designed by Ron Rivest, RSA was originally part of RSA Security and is a patented cryptographic product. It is a byte-oriented stream cipher with a variable key length that is very simple, but it works. The RC4 algorithm is widely used in the SSL/TLS protocol and the WEP/WPA protocol.

Basic Process

RC4 mainly consists of three processes

  • Initialize the S and T arrays.
  • Initialize the replacement S.
  • Generate a key stream.

Initializing S and T arrays

The code to initialize S and T is as follows

for i = 0 to 255 do

    S[i] = i

    T[i] = K[i mod keylen])

image-20180714192918699

Initialization replacement S

j = 0

for i = 0 to 255 do 

    j = (j + S[i] + T[i]) (mod 256) 

    swap (S[i], S[j])

image-20180714193448454

Generating a stream key

i = j = 0 

for each message byte b

i = (i + 1) (toward 256)
    j = (j + S[i]) (mod 256)

    swap(S[i], S[j])

    t = (S[i] + S[j]) (mod 256) 

    print S[t]

image-20180714193537976

We generally refer to the first two parts as KSA and the last part to PRGA.

Attack method

To be added.


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