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Asked: 2026-05-10T20:56:36+00:00

Inside my code I’m generating hashes of URLs, (which are practically of unbounded length).

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Inside my code I’m generating hashes of URLs, (which are practically of unbounded length). I’m currently using sha1(), which I know has a tiny chance of a collision, but I have up to 255 bytes to store the hash in so feel that I might as well use that available space to lower the chance of collision even further.

Is there either:

  1. Another PHP hash function with a longer or customisable hash length?
  2. A way of using a fixed-length hash function like sha1 with a variable length input to generate a longer hash?

Or, is sha1’s 20-byte hash good enough for anything and I should stop worrying about it?

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  1. Or, is sha1’s 20-byte has good enough for anything and I should stop worrying about it?

    Exactly.

    Hashtables, Pigeonholes, and Birthdays
    http://www.codinghorror.com/blog/archives/001014.html

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