# How to calculate hash sum of a string (using java)?

조회 수: 100(최근 30일)
Sebastian Holmqvist 2012년 8월 6일
답변: Oliver Woodford 2016년 5월 5일
Couldn't find this very easily (without including a bunch of c-mex files etc) so I thought I'd post it here for future reference. I prefer using java methods to avoid dependencies.
Question:
Using java, how to create a MD5 (or SHA1 etc) hash sum of a string?

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### 채택된 답변

Sebastian Holmqvist 2012년 8월 6일
편집: Sebastian Holmqvist 2012년 8월 6일
Solution:
The trick here is to input an ascii representation of your string (hence, the double(string) call). MessageDigest outputs 16 bytes which represents 32 chars. So we use BigInteger to convert the bytes to that radix.
import java.security.*;
import java.math.*;
md = MessageDigest.getInstance('MD5');
bi = BigInteger(1, hash);
char(bi.toString(16))
ans =
b99e5935368933bafefed10b99bb0489
##### 댓글 수: 1표시숨기기 없음
Nick Hilton 2015년 10월 14일
I found a bug, BigInteger.toString(16) won't fill with zeros. For example, if the BigInter's hex representation was '0abc', toString(16) will only return 'abc'.
Fixing this requires using the java.lang.String.format method:
import java.lang.String;
char(String.format('%032x', bi));
MD5 returns 32 hex values, but if one were to change the message digest to 'SHA-256', then one needs to use:
char(String.format('%064x', bi));
This will guarantee a fixed width hash filled with '0'.

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### 추가 답변(1개)

Oliver Woodford 2016년 5월 5일
A similar solution:
%STRING2HASH Convert a string to a 64 char hex hash string (256 bit hash)
%
% hash = string2hash(string)
%
%IN:
% string - a string!
%
%OUT:
% hash - a 64 character string, encoding the 256 bit SHA hash of string
function hash = string2hash(string)
persistent md
if isempty(md)
md = java.security.MessageDigest.getInstance('SHA-256');
end
hash = sprintf('%2.2x', typecast(md.digest(uint8(string)), 'uint8')');
end

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