delphi crypto api decode

Question

I use crypto api WCrypt2 in my project for md5 crypt but i dont know to decode. Can you provide me the decode function for crypto api?

In my project i need to use this encryption code from bellow. The decode function must work with the Label1 and Edit1.Bouth are included in form startup, but for decode i will use a Button1

here is my code:

unit HUID;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, IdGlobal, IdHash, IdHashMessageDigest, WCrypt2;

type
  TForm1 = class(TForm)        
    Edit1: TEdit;
    Label1: TLabel;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function GetEnvVarValue(const VarName: string): string;
var
  BufSize: Integer;  // buffer size required for value
begin
  // Get required buffer size (inc. terminal #0)
  BufSize := GetEnvironmentVariable(PChar(VarName), nil, 0);
  if BufSize > 0 then
  begin
    // Read env var value into result string
    SetLength(Result, BufSize - 1);
    GetEnvironmentVariable(PChar(VarName),
    PChar(Result), BufSize);
  end
  else
    // No such environment variable
    Result := '';
end;

function md5(const Input: string): string;
var
  i: Integer;
  pbContent: PByte;
  dwHashBytes: Cardinal;
  hHash: HCRYPTHASH;
  hCryptProvider: HCRYPTPROV;
  bHash: array[0..$7f] of Byte;
begin
  Result := '';
  dwHashBytes := 16;
  pbContent := Pointer(PChar(Input));

  if CryptAcquireContext(@hCryptProvider, nil, nil, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT or CRYPT_MACHINE_KEYSET) then
  begin
    if CryptCreateHash(hCryptProvider, CALG_MD5, 0, 0, @hHash) then
    begin
      if CryptHashData(hHash, pbContent, Length(Input) * sizeof(Char), 0) then
      begin
        if CryptGetHashParam(hHash, HP_HASHVAL, @bHash[0], @dwHashBytes, 0) then
        begin
          for i := 0 to dwHashBytes - 1 do
          begin
            Result := Result + Format('%.2x', [bHash[i]]);
          end;
        end;
      end;
      CryptDestroyHash(hHash);
    end;
    CryptReleaseContext(hCryptProvider, 0);
  end;
  Result := AnsiLowerCase(Result);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Label1.Caption :=  (GetEnvVarValue('PROCESSOR_REVISION')+GetEnvVarValue('PROCESSOR_LEVEL')+GetEnvVarValue('NUMBER_OF_PROCESSORS')+GetEnvVarValue('Cor_Debugging_Control_424242'));
  Edit1.Text := md5(Label1.Caption);
end;

end.

Answer 1

MD5 is a one-way hash.
It is used for signing information and checking passwords.

Encryption
If you want to encrypt data (eg to send it securely across the wire) You need to use a cipher like AES or 3DES.

If you replace the MD5 call with AES decryption becomes easy.
AES is a symmetric cipher, meaning that encryption and decryption uses the same key (although not the same operation).

See the following wiki pages for more info:

• Cryptographic hash function
• Symmetric key algorithm

Signing
If you want to use the MD5 function for password encryption, then you're making two mistakes:

1. MD5 is not secure anymore, use SHA2 or SHA3 instead.
2. You need to salt any passwords that you hash, see: How does password salt help against a rainbow table attack?

In order to check a password you rehash it using the same salt and check to see if the same result comes out.