asked on

key based encrypt, decrypt string for both delphi and C#

This question has been asked and accepted here before, however the answer was not good enough since the encryption was a static shift based on an integer value.
I am after two simple functions to encrypt and decrypt a string based on a key (salt, string) for both Delphi and C# without using any extra libraries. A simple character shift would be ok as long as it is a key based shift and encrypted string characters are ANSI compatible.

Eddie Shipman

Sounds like homework, to me...

mtasking

ASKER

You are right Eddie, never thought about that - I should give you 500 points for this answer. I am sure you are a very successful programmer, proficient in several different languages that hates to waste his companys time and money by writing code that lives in somebodys snippet collection and only requires a copy and paste. Let me guess, you are a seasoned developer making lots of money with such comments, arent you? LOL

ThievingSix

http://delphi.about.com/od/humorandfun/a/fdacfileencrypt.htm

mtasking

ASKER

This is a link to file encryption in Delphi.
I am after two simple functions to encrypt and decrypt a string based on a key (salt, string) for both Delphi and C# without using any extra libraries. A simple character shift would be ok as long as it is a key based shift and encrypted string characters are ANSI compatible.

Johnjces

Maybe this could help you.

I am not an encryption person at all; do not know exactly what is meant by a 'salt' but this might get you headed in a direction you want to go. The 'salt' key might be the 'StartKey' which is made up with some other 'salt' keys.

It does xor character shifts.

John

{*******************************************************
 * Standard Encryption algorithm - Copied from Borland *
 *******************************************************}
function Encrypt(const InString:string; StartKey,MultKey,AddKey:Integer): string;
var
  I : Byte;
begin
  Result := '';
  for I := 1 to Length(InString) do
  begin
    Result := Result + CHAR(Byte(InString[I]) xor (StartKey shr 8));
    StartKey := (Byte(Result[I]) + StartKey) * MultKey + AddKey;
  end;
end;
{*******************************************************
 * Standard Decryption algorithm - Copied from Borland *
 *******************************************************}
function Decrypt(const InString:string; StartKey,MultKey,AddKey:Integer): string;
var
  I : Byte;
begin
  Result := '';
  for I := 1 to Length(InString) do
  begin
    Result := Result + CHAR(Byte(InString[I]) xor (StartKey shr 8));
    StartKey := (Byte(InString[I]) + StartKey) * MultKey + AddKey;
  end;
end;

Open in new window

Johnjces

PS... this could be the same answer provided in whatever post you were referring to in your original Q. I don't know but links to previously found stuff can be helpful so no one gives you repeat information.

John

mtasking

ASKER

Thanks for your answer, this is certainly a start. I changed it up so it can be used with a string key instead of 3 numbers and tested:

ShowMessage(Encrypt('123abc', '2kewl'));
ShowMessage(Decrypt(Encrypt('123abc', '2kewl'), '2kewl'));

Anybody up to translate to C# for point split?

function Encrypt(const InString:string; Salt:string): string;
var
  i : Byte;
  StartKey, MultKey, AddKey: Word;
begin
  Result := '';
  if (Salt = '') then begin
    Result := InString;
  end
  else begin
    StartKey := Length(Salt);
    MultKey := Ord(Salt[1]);
    AddKey := 0;
    for i := 1 to Length(Salt) - 1 do AddKey := AddKey + Ord(Salt[i]);
    for i := 1 to Length(InString) do
    begin
      Result := Result + CHAR(Byte(InString[i]) xor (StartKey shr 8));
      StartKey := (Byte(Result[i]) + StartKey) * MultKey + AddKey;
    end;
  end;
end;
 
function Decrypt(const InString:string; Salt:string): string;
var
  i : Byte;
  StartKey, MultKey, AddKey: Word;
begin
  Result := '';
  if (Salt = '') then begin
    Result := InString;
  end
  else begin
    StartKey := Ord(Salt[1]);
    MultKey := Length(Salt);
    AddKey := 0;
    for i := 1 to Length(Salt) - 1 do AddKey := AddKey + Ord(Salt[i]);
    for i := 1 to Length(InString) do
    begin
      Result := Result + CHAR(Byte(InString[i]) xor (StartKey shr 8));
      StartKey := (Byte(InString[i]) + StartKey) * MultKey + AddKey;
    end;
  end;
end;

Open in new window

ASKER CERTIFIED SOLUTION

Johnjces

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial

mtasking

ASKER

Great, thanks.

Rob Robal

Does not work