PHP hash function with long output length?

Question

Inside my code, I generate hashes of URLs (which are of almost unlimited length). I am currently using sha1 (), which I know has a tiny chance of collision, but I have up to 255 bytes to store the hash, so I can use this available space to reduce the likelihood of a collision even later on.

Whether there is a:

• Another PHP hash function with a longer or custom hash length?
• How to use a fixed length hash function like sha1 with an input variable length to generate a longer hash?

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

Answer 1

, 20- sha1, -, ?

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

Answer 2

... http://www.cryptography.com/cnews/hash.html

: SHA-1?
A: 2 ^ 69 ( 590 . .) -

, ... ^ _ ^

Answer 3

, 256- 512- (32 64 ).

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, , md5 sha-256.

Answer 4

/ ( ) ?

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, -, ?

Answer 5

, , , , . :

found = false
hv = hash(urlValue)
if table[hash,url] contains pair (hv,urlValue)
   found = true
endif

if (not found)
   insert table (hv,urlValue)
endif

hash, . (, url) - , , , , URL-. -. , URL- , .

Answer 6

, , URL.

, URL- 40 - 5 : SHA1 1-8, SHA1 9-16, SHA1 17-24... .. 2 ⁸⁰⁰ 2 ^{(69 * 5)}= 2 ³⁴⁵= 7.2 * 10 ¹⁰³ .

, , .

Answer 7

, , - . .