Editing RC4 (section)

===VMPC===
{{Main article|Variably Modified Permutation Composition}}
Variably Modified Permutation Composition (VMPC) is another RC4 variant.<ref>{{Citation |chapter=VMPC One-Way Function and Stream Cipher |chapter-url=http://www.vmpcfunction.com/vmpc.pdf |author=Bartosz Zoltak |year=2004 |title=Fast Software Encryption, FSE 2004 |series=Lecture Notes in Computer Science |volume=3017 |publisher=Springer-Verlag |doi=10.1007/978-3-540-25937-4_14 |isbn=978-3-540-22171-5 |pages=210–225 |access-date=2011-11-04|url=https://www.iacr.org/archive/fse2004/30170209/30170209.pdf |citeseerx=10.1.1.469.8297 }}</ref> It uses similar key schedule as RC4, with
{{mono|1=j := S[(j + S[i] + key[i mod keylength]) mod 256]}} iterating 3 × 256 = 768 times rather than 256, and with an optional additional 768 iterations to incorporate an initial vector. The output generation function operates as follows:

 <span style="color: green;">''All arithmetic is performed modulo 256.''</span>
 i := 0
 '''while''' GeneratingOutput:
     j := S[j + S[i]]
     
     '''output''' S[S[S[j]] + 1]
     Swap S[i] and S[j]          <span style="color: green;">(''b := S[j]; S[j] := S[i]; S[i] := b)'')</span>
     
     i := i + 1
 '''endwhile'''

This was attacked in the same papers as RC4A, and can be distinguished within 2<sup>38</sup> output bytes.<ref name="maximov">{{Cite web |url=http://www.cryptolounge.org/wiki/RC4A |title=CryptoLounge: RC4A |access-date=4 November 2011 |archive-url=https://web.archive.org/web/20111001012601/http://www.cryptolounge.org/wiki/RC4A |archive-date=1 October 2011 |url-status=dead |df=dmy-all }}</ref><ref name="nec"/>