Which hashing algorithm provides the longest outpu

Question

I was curious about which hashing method usable by PHP's crypt function provides the longest output, and also, if the length of the output was relative at the chance of their being a collision of two hashes.

Answer 1

See this comment on the PHP docs for hash():

alg       strlen hash (cropped)

md2           32 a9046c73e00331af68917d3804f70655                  
md4           32 866437cb7a794bce2b727acc0362ee27
md5           32 5d41402abc4b2a76b9719d911017c592
sha1          40 aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d
sha256        64 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e730
sha384        96 59e1748777448c69de6b800d7a33bbfb9ff1b463e44354c3553
sha512       128 9b71d224bd62f3785d96d46ad3ea3d73319bfbc2890caadae2d
ripemd128     32 789d569f08ed7055e94b4289a4195012
ripemd160     40 108f07b8382412612c048d07d13f814118445acd
ripemd256     64 cc1d2594aece0a064b7aed75a57283d9490fd5705ed3d66bf9a
ripemd320     80 eb0cf45114c56a8421fbcb33430fa22e0cd607560a88bbe14ce
whirlpool    128 0a25f55d7308eca6b9567a7ed3bd1b46327f0f1ffdc804dd8bb
tiger128,3    32 a78862336f7ffd2c8a3874f89b1b74f2
tiger160,3    40 a78862336f7ffd2c8a3874f89b1b74f2f27bdbca
tiger192,3    48 a78862336f7ffd2c8a3874f89b1b74f2f27bdbca39660254
tiger128,4    32 1c2a939f230ee5e828f5d0eae5947135
tiger160,4    40 1c2a939f230ee5e828f5d0eae5947135741cd0ae
tiger192,4    48 1c2a939f230ee5e828f5d0eae5947135741cd0aefeeb2adc
snefru        64 7c5f22b1a92d9470efea37ec6ed00b2357a4ce3c41aa6e28e3b
gost          64 a7eb5d08ddf2363f1ea0317a803fcef81d33863c8b2f9f6d7d1
adler32        8 062c0215
crc32          8 3d653119
crc32b         8 3610a686
haval128,3    32 85c3e4fac0ba4d85519978fdc3d1d9be
haval160,3    40 0e53b29ad41cea507a343cdd8b62106864f6b3fe
haval192,3    48 bfaf81218bbb8ee51b600f5088c4b8601558ff56e2de1c4f
haval224,3    56 92d0e3354be5d525616f217660e0f860b5d472a9cb99d6766be
haval256,3    64 26718e4fb05595cb8703a672a8ae91eea071cac5e7426173d4c
haval128,4    32 fe10754e0b31d69d4ece9c7a46e044e5
haval160,4    40 b9afd44b015f8afce44e4e02d8b908ed857afbd1
haval192,4    48 ae73833a09e84691d0214f360ee5027396f12599e3618118
haval224,4    56 e1ad67dc7a5901496b15dab92c2715de4b120af2baf661ecd92
haval256,4    64 2d39577df3a6a63168826b2a10f07a65a676f5776a0772e0a87
haval128,5    32 d20e920d5be9d9d34855accb501d1987
haval160,5    40 dac5e2024bfea142e53d1422b90c9ee2c8187cc6
haval192,5    48 bbb99b1e989ec3174019b20792fd92dd67175c2ff6ce5965
haval224,5    56 aa6551d75e33a9c5cd4141e9a068b1fc7b6d847f85c3ab16295
haval256,5    64 348298791817d5088a6de6c1b6364756d404a50bd64e645035f

So, the longest would be sha512 or whirlpool. Since you mentioned crypt(), you're down to CRYPT_SHA512, but you don't necessarily need to use it if you have hash() available.