some quick notes re: md5

dobbertin 1996 was the first, as far as i know, to show common values for the *compression algorithm* inside md5. RFC1828, security considerations section, gives a high level view of this.

in essence this would allow an attacker to exploit under *very* stringent (read peculiar) conditions digital signatures of files, for which md5 is most commonly used. still, Schneier counterpane does not seem to like it.

so yes, you might want to md5 twice. but - the general consensus is that SHA is more secure. here is a (yet another) wee gem from Adam Back's cypherspace site which computes it, instead.

#!/usr/bin/perl -iD9T4C`>_-JXF8NMS^$#)4=L/2X?!:@GF9;MGKH8\;O-S*8L'6
@A=unpack"N*",unpack u,$^I;@K=splice@A,5,4;sub M{($x=pop)-($m=1+~0)*in
+t$x/$m};
sub L{$n=pop;($x=pop)<<$n|2**$n-1&$x>>32-$n}@F=(sub{$b&($c^$d)^$d},$S=
+sub{$b^$c
^$d},sub{($b|$c)&$d|$b&$c},$S);do{$l+=$r=read STDIN,$_,64;$r++,$_.="\x
+80"if$r<
64&&!$p++;@W=unpack N16,$_."\0"x7;$W[15]=$l*8 if$r<57;for(16..79){push
+@W,L$W[$_
-3]^$W[$_-8]^$W[$_-14]^$W[$_-16],1}($a,$b,$c,$d,$e)=@A;for(0..79){$t=M
+&{$F[$_/
20]}+$e+$W[$_]+$K[$_/20]+L$a,5;$e=$d;$d=$c;$c=L$b,30;$b=$a;$a=$t}$v='a
+';@A=map{
M$_+${$v++}}@A}while$r>56;printf'%.8x'x5 ."\n",@A

[download]
hope that helps,

wufnik

...in the world of the mules there are no rules

In reply to Re: Why applying MD5 hash twice? by wufnik
in thread Why applying MD5 hash twice? by huguei

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