UUHash

UUHash is a hash algorithm that is used by clients of the FastTrack network. In a short time checksums for very large files can be created, even on low-performance computers. However, the checksum is formed only for some parts of the file. This weakness makes finding hash collisions, and distortions or corruptions of the rest of the file remain unnoticed, since the checksum is not thereby affected.

UUHash used as Kazaa and the RIAA uses this weakness to spread corrupted or damaged files on the network.

Algorithm

UUHash forms a MD5 checksum on the first 300 kB of the file, and then at intervals of 2 ^ n MB ( n = 0 and is increased by 1 until the end of file is reached) for the next 300 kB blocks. For UUHash uses its own Smallhash function. At the end is formed in the last 300 KB of the file checksum. If the last 300 kB overlaps n block with the last 2 ^, this is previously discarded.

Example:

The 128 bit MD5 checksum and the 32 bit Smallhash then make up the 160-bit checksum for the identification of the file in the FastTrack network. The sum so obtained is then encoded with Base64 and returns the UUHash.

Sig2Dat

The name UUHash is actually an unfortunate choice. This originates from the sig2dat ( version of 22 January 2008 on the Internet Archive ) tool. This creates URIs reference files for Kazaa. The URIs (the format does not match the RFC standard. ) ​​Sig2dat see with this:

Sig2dat :/ / | file: surprise.mp3 | Length: 5845871Bytes | UUHash: = 1LDYkHDl65OprVz37xN1VSo9b00 = But UUHash use Base64 encoding for the checksum and not the checksum itself.

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