PS: Some ppl suggest to combine a small CRC hash with filesize (which is allready in Queryhits, not in Queries or other Gnutella descriptors).... let's play around with this idea. This would be a 32 bit hash + 32 bit filesize (taken from Gnutella protocol v0.4) = 64 bit key to use. Perhaps it would be more unique to use a real hash of 64 bit instead of the 64 bit CRC+filesize combo, e.g. an truncated MD5?

Here an overview of minimum possibilities:
* CRC-32, size 32 bit
* CRC-32 filesize combo, size 64 bit
* MD5 truncated, size 64 bit
* MD5, size 128 bit

Notes: I have choosen MD5 in this case, because it is the smallest and fastest compared to other hashs (SHA1, Tiger, Snefru). The CRC-32 alone is too small. The CRC-filesize combo might be enough, the truncated 64 bit MD5 might be mathematically more unique while it wastes 32 bit information in Queryhits (not in Query, GET, PUSHS). The next higher alternative is a 128 Bit MD5, e.g FastTrack uses an MD5 hash AFAIK.

I'm not sure if a minimum alternative is the best solution for Gnutella's future. Perhaps a 64 bit key does make us happy now, in future with more superpeers and bigger horizons we might want to have a bigger hash (MD5 or SHA1)?

An possibility could be an encoding alla HUGE. The hash has an prefix telling the hash type. For binary Gnutella messages (Query/Queryhits) this could be a payload like: byte 0 = hash type, more bytes = binary hash. The protocoll defines a list of known hash, while clients need a common solution, this list will be short, e.g start with CRC-filesize combo today and use SHA1 in future. In HTTP-alike Gnutella messages we can work with encoded hashs (not binary), similar to the HUGE proposal [1].

Conclusion: I have none. I suggest to implement and test a minimum solution (CRC32-filesize combo) and a bigger hash (MD5 or SHA1) for a while. With more experience in a real world environment we can hopefully find a suitable solution. Feedback, tests and mathematical analysis are welcome!

[1] "HUGE" - http://groups.yahoo.com/group/the_gd...roposals/HUGE/ (Yahoo account required)