MultiSwap

In <a href="/facts/Cryptography/e94PEVau">cryptography</a>, MultiSwap is a <a href="/facts/Block_cipher/MJywAyfQ">block cipher</a>/<a href="/facts/Message_authentication_code/mXxCP5Yl">MAC</a> created by <a href="/facts/Microsoft/nGIDDXdx">Microsoft</a> in 1999 as part of its <a href="/facts/Windows_Media_DRM/YIJYjdk2">Windows Media DRM</a> service (WMDRM). Microsoft's internal name for the algorithm is not publicly known; it was dubbed MultiSwap in a 2001 report on WMDRM under the pseudonym "Beale Screamer".
The cipher has a <a href="/facts/Block_size_(cryptography)/QdUI7u7v">block size</a> of 64 bits, but the two halves are processed nearly separately. All arithmetic operations are performed <a href="/facts/Modular_arithmetic/0wtRa5dU">mod</a> 232. In the encryption process, each half block has added to it the output of the previous half block. Next it undergoes 5 multiplications by odd 32-bit subkeys, each followed by a swap of its 16-bit halves. Then a final subkey is added to it. As the half blocks use separate subkeys, and the multipliers are forced to be odd, the total <a href="/facts/Key_size/1amrJ13L">key size</a> is 374 bits. The name MultiSwap comes from the cipher's multiplications and swaps. WMDRM uses this algorithm only as a MAC, never for encryption.
Borisov, et al. applied a multiplicative form of <a href="/facts/Differential_cryptanalysis/84yp0SDC">differential cryptanalysis</a> to break MultiSwap.

<ul><li>Beale Screamer (18 October 2001). <a href="http://cryptome.org/ms-drm.htm">"Microsoft's Digital Rights Management Scheme – Technical Details"</a>. Retrieved 20 September 2007.</li>
<li><a href="/facts/Nikita_Borisov/fICtIxYx">Nikita Borisov</a>, Monica Chew, Rob Johnson, <a href="/facts/David_A._Wagner/ewC269Uo">David Wagner</a>. <a href="https://web.archive.org/web/20160305190456/http://www3.cs.stonybrook.edu/~rob/multiswap/">"Cryptanalysis of MultiSwap"</a>. Archived from <a href="http://www.cs.sunysb.edu/~rob/multiswap/">the original</a> on 5 March 2016. Retrieved 9 October 2010.{{cite web}}: CS1 maint: multiple names: authors list (link)</li>
<li>Borisov, Chew, Johnson, Wagner (February 2002). <a href="http://citeseer.ist.psu.edu/672650.html">Multiplicative Differentials</a> (<a href="/facts/PDF/C9Mn1vYL">PDF</a>/<a href="/facts/PostScript/h2XwbcmC">PostScript</a>). 9th International Workshop on <a href="/facts/Fast_Software_Encryption/TgVIMDmb">Fast Software Encryption</a> (FSE '02). <a href="/facts/Leuven/zkKTDkzH">Leuven</a>: <a href="/facts/Springer-Verlag/nAesf6nT">Springer-Verlag</a>. pp. 17–33. Retrieved 3 January 2007.{{cite conference}}: CS1 maint: multiple names: authors list (link)</li></ul>

MultiSwap open-in-new

MultiSwap