On 2010-Jul-09 06:46:54 +0800, Edward Ned Harvey <solar...@nedharvey.com> wrote: >md5 is significantly slower (but surprisingly not much slower) and it's a >cryptographic hash. Probably not necessary for your needs.
As someone else has pointed out, MD5 is no longer considered secure (neither is SHA-1). If you want cryptographic hashing, you should probably use SHA-256 for now and be prepared to migrate to SHA-3 once it is announced. Unfortunately, SHA-256 is significantly slower than MD5 (about 4 times on a P-4, about 3 times on a SPARC-IV) and no cryptographic hash is amenable to multi-threading . The new crypto instructions on some of Intel's recent offerings may help performance (and it's likely that they will help more with SHA-3). >And one more thing. No matter how strong your hash is, unless your hash is >just as big as your file, collisions happen. Don't assume data is the same >just because hash is the same, if you care about your data. Always >byte-level verify every block or file whose hash matches some other hash. In theory, collisions happen. In practice, given a cryptographic hash, if you can find two different blocks or files that produce the same output, please publicise it widely as you have broken that hash function. -- Peter Jeremy
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