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Complexity of recovering the internal state of the VMPC Stream Cipher


Over 2^900 operations are estimated to be required to recover the Cipher's internal state from its output. A method similar in its foundations to the Forward Tracking Algorithm, proposed by S. Mister and S.E. Tavares in "Cryptanalysis of RC4-like Ciphers" at Selected Areas in Cryptography 1998, was applied to break the VMPC Stream Cipher. On average half of all the possible values of about 102 of the elements of the Cipher's internal permutation need to be tested before the whole permutation can be recovered, which is approximated to take on average over 2^900 steps.

by Bartosz Zoltak

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