convert char to char such as encryption

Question

How to make a simple encryption decryption?
2 pieces of make edit box and a button in the project, then I write something in editbox1 and then press button1 in editbox2 generate some keys in such settings ..

a: = 1; b: = 2; c: = 3; d: = 4; e: = 5; f: = 6; g: = 7; h: = 8; i: = 9; j: = 0; k: = #; l: = $; m: =%; n: = ~; o: = *;

and then with the symbol say
a: = 1; it means: a is 1 if at editbox2

letters (A) be the number 1 subparagraph (B) be the number 2 subparagraph (C) be the number 3 simple conversion .. so make a simple substitution cipher and decryption

Answer 1

Here is a simple substitution cipher

const
  CPlain = 'abcdefghijklmno';
  CCrypt = '1234567890#$%~*';

function Transcode( const AStr, ALookupA, ALookupB : string ): string;
var
  LIdx, LCharIdx : integer;
begin
  // the result has the same length as the input string
  SetLength( Result, Length( AStr ) );
  // walk through the whole string
  for LIdx := 1 to Length( AStr ) do
  begin
    // find position of char in LookupA
    LCharIdx := Pos( AStr[LIdx], ALookupA );
    // use the char from LookupB at the previous position
    Result[LIdx] := ALookupB[LCharIdx];
  end;
end;

function Encrypt( const AStr : string ) : string;
begin
  // from plain text to crypt text
  Result := Transcode( AStr, CPlain, CCrypt );
end;

function Decrypt( const AStr : string ) : string;
begin
  // from crypt text to plain text
  Result := Transcode( AStr, CCrypt, CPlain );
end;