Reverse a hash function?

[user]

Does it possible to decrypt the hash from this function?

Delphi-Quellcode:

type TAdlerBytes = array[1..MAXINT] of Byte;
     TAdlerArray = array[0..16] of Integer;
     PAdlerBytes = ^TAdlerBytes;

implementation

{$R *.dfm}
function FNV32(PAB:PAdlerBytes;ACount:Integer):DWORD;
var i,APrime:DWORD;
begin
  APrime:= 16777619;
  Result:=2166136261;
  for i:=1 to ACount do
  begin
    Result:=Result*APrime;
    Result:=Result xor PAB^[i];
  end;
  //FNV stands for Fowler-Noll-Vo.
  //Read up on FNV at http://www.isthe.com/chongo/tech/comp/fnv
end;
procedure TForm1.FormCreate(Sender: TObject);
var
i:dword;
s:string;
begin
s:='aaabbbffggfd';
i:=fnv32(PAdlerBytes(s),length(s));
OutputDebugString(pchar(inttostr(i)));
end;

[JasonDX]

Zitat von user:

Does it possible to decrypt the hash from this function?

Well, you map a string of arbitrary length to a finite field, so you do have some collisions. It therefore is not always possible to 'decrypt' the hash (in the sense of getting s from h(s), h being the hash function), but you can always find a string s' that hashes to the same value, hence h(s) = h(s'). The next question would then propably be how long it takes to find such string.

greetz
Mike

[mkinzler]

Not being reversible is the nature of a hash function

[himitsu]

hash = one-way encryption

This can not be reversed.


[edit]
Wo kommen denn "plötzlich" die vielen Antworten her?
(grad eben waren die noch nicht da)

[user]

Hmm.. I think reversing the function is bad idea. I am on panic and I have wrong concept in my program. Sorry, I'm still learning. Thanks.