hash - The maximum length of a message that can be hashed with WHIRLPOOL -


i'm wondering maximum length. read wikipedia takes message of length less 2^256 bits. mean 2 power of 256? also, more secure hash password multiple times? example:

whirlpool(whirlpool(whirlpool(whirlpool("passw0rd"))))

or increase risk of collisions?

yes, mean 2^256 bits. of course, there 2^3 bits in byte, have maximum space of 2^253 bytes. nothing worry about.

yes, better hash multiple times. no, don't have worry "cycles" (much). many pseudo random number generators using hashes same way. hash algorithms should not loose information , should not have short cycle time.

passwords hashes should calculated using password based key derivation functions. "key" stored. pbkdf's may use hashes (e.g. pbkdf2) or keyed block ciphers (bcrypt). kdf's using message authentication codes (hmac or mac) instead of directly using underlying hash algorithm or block cipher.

input pbkdf's salt , iteration count. iteration count used make harder attacker brute force system trying out kinds of passwords. it's same did above whirlpool. iteration count somewhere between 1 , 10 thousand. more data mixed in in each iteration.

more importantly, (password specific) salt used make sure duplicate passwords cannot detected , avoid attacks using rainbow tables. salt 64 128 bits. salt , iteration count should stored "hash".

finally, better use nist vetted hash algorithm such sha-512 instead of whirlpool.


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