What is Variably Modified Permutation Composition mean? VMPC (Variably Modified Permutation Composition) is a stream cipher similar to thewell known and popular cipher RC4 designed by Ron Rivest. It was designed by Bartosz Żółtak, presented in 2004 at the Fast Software Encryption conference. VMPC is a modification of the RC4 cipher.
The core of the cipher is the VMPC function, a transformation of n-element permutations defined as:
for x
from 0
to n-1: g(x) = VMPC(f)(x) = f(f(f(x))+1)
The function was designed such that inverting it, i.e. obtaining f from g, would be a complex problem. According to computer simulations the average number of operations required to recover f from g for a 16-element permutation is about 211; for 64-element permutation, about 253; and for a 256-element permutation, about 2260.
In 2006 at Cambridge University, Kamil Kulesza investigated the problem of inverting VMPC and concluded "results indicate that VMPC is not a good candidate for a cryptographic one-way function".
The VMPC function is used in an encryption algorithm – the VMPC stream cipher. The algorithm allows for efficient in software implementations; to encrypt L bytes of plaintext do:
All arithmetic is performed modulo 256.i := 0
while GeneratingOutput: a := S[i] j := S[j + a]
output S[S[S[j]] + 1] swap S[i] and S[j] (
b := S[j]; S[i] := b; S[j] := a)) i := i + 1
endwhileWhere 256-element permutation P and integer value s are obtained from the encryption password using the VMPC-KSA (Key Scheduling Algorithm).
reference
Posted on 26 Apr 2022, this text provides information on General related to Miscellaneous in General. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.