read a hash
lazarus / 9-Editor

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emil · 2015-03-14 22:34

hello guys
im begginer
i want to hash a string:
s := MD5Print(MD5String('hei');

after, i want to get the value 'hei' using S

it is possible?

i need to hash a fille, i want to make it unreadable

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engkin · 2015-03-14 23:31

Quote from: emil on March 14, 2015, 11:34:52 pmhello guys
im begginer
i want to hash a string:
s := MD5Print(MD5String('hei');

after, i want to get the value 'hei' using S

it is possible?

No, it is not possible. In general, you can *not* get the original
string from a hash. Moreover, two different strings could have the
same hash code. MD5 hashing gives 16 bytes (32 hex digits) regardless
of the string.

Quote from: emil on March 14, 2015, 11:34:52 pmi need to hash a fille,
i want to make it unreadable

Simplest way is to use xor:
Code: [Select]var
  s: string;
  i: Integer;
begin
  s := 'Apples';
  //Encode
  for i := 1 to Length(s) do
    s[i] := Char(Byte(s[i]) xor $67);
  WriteLn(s);

  //Decode
  for i := 1 to Length(s) do
    s[i] := Char(Byte(s[i]) xor $67);
  WriteLn(s);

$67 is just an example, use a number of your own.

For a bit better way that produces "readable" text, use Base64
encoding from unit base64:
Code: [Select]program Project1;
uses
  base64;

var
  s: string;
begin
  s := 'Apples';

  //Encode
  s := EncodeStringBase64(s);
  WriteLn(s);

  //Decode
  s := DecodeStringBase64(s);
  WriteLn(s);

  ReadLn;
end.

Both are not secure. For a bit of security try BlowFish, for instance.
Here is a nice example by ChrisF.

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Leledumbo · 2015-03-15 05:11

Quote from: emil on March 14, 2015, 11:34:52 pmit is possible?
No, hash is one way, you can't retrieve back the original string
having only the hash.
Quote from: emil on March 14, 2015, 11:34:52 pmi need to hash a fille,
i want to make it unreadable
Use encryption, not hash.