i need a decoding algorithm of SHA-512?
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please suggest me... if decoding algorithm is not available then please tell me how can i decode the hash value generated by coding algorithm?
3 个评论
Jan
2013-6-6
I've deleted the double posting.
Walter Roberson
2013-6-6
This is a duplicate of http://www.mathworks.co.uk/matlabcentral/answers/77801-this-algorithm-to-generate-the-hash-value-using-text-character-my-name-is-saurabh-singh-how-i-can except without the code and with a minor bit more explanation.
SAURABH
2013-6-7
采纳的回答
Jan
2013-6-6
1 个投票
You cannot decode a hash. This is the purpose of hashes.
Note that a 512-bit hash is not unique, when it is calculated for a message with 513 or more bits.
8 个评论
Walter Roberson
2013-6-6
The difficulty of reversing a hash is what makes any particular hash useful for cryptographic purposes, but it is not the purpose of hashes.
Jan
2013-6-6
@Walter: You are right. See [EDITED]
Walter Roberson
2013-6-6
[EDITED] does not seem to have shown up ?
SAURABH
2013-6-7
Walter Roberson
2013-6-7
A hash function is any algorithm or subroutine that maps data sets of variable length to data sets of a fixed length. For example, a person's name, having a variable length, could be hashed to a single integer of bounded size.
Notice that these functions are not required to be injective (because distinct inputs may map to the same output) and are not required to be surjective (there may be elements of the output range that turn out to be impossible to generate.
Jan
2013-6-7
@Walter: There seems to be a serious problem for this thread. I've posted a longer comment two times, but they disappeared when I reloaded the thread. Then I added the comment as [EDITED] in the answer, but it vanished also obviously. Not I hesitate to waste more time again and check at first, if at least this comment is accepted.
Walter Roberson
2013-6-7
meta comment reached here
Yes, even after relaoding the above comment is still there. Strange! So I try it again:
@Walter: Yes, you are right. My message is really too sloppy. A short message can be reconstructed from the hash, but this consumes much time and a brute-force-attack is a fair approach. But decoding is not the intention of hashes.
Using "purpose" as synonym for "not the intention" was not smart.
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