Question

I’d like to AES-128 encrypt a string in Delphi with a password. I’d like to upload this to my server and be able to decrypt given the same password in C#.

In Delphi, I’m using TurboPower LockBox 3:

function EncryptText_AES_128(input: string; password: string): string;
var
  Codec: TCodec;
  CipherText: AnsiString;
begin
  Codec := TCodec.Create(nil);
  try
    Codec.CryptoLibrary := TCryptographicLibrary.Create(Codec);
    //
    Codec.StreamCipherId := BlockCipher_ProgID;
    Codec.BlockCipherId := Format(AES_ProgId, [128]);
    Codec.ChainModeId := CBC_ProgId;
    //
    Codec.Password := Password;
    Codec.EncryptString(input, CipherText);
    //
    Result := string(CipherText);
  finally
    Codec.Free;
  end;
end;

How can I decrypt the resulting string in C#? I can change the Delphi code. Nothing is in production yet. I’m not even stuck on using LockBox. But, I would like to avoid putting this in a DLL for P/Invoke.

(My example shows that my encrypted sequence is itself a string. This is not a requirement for me. A stream of bytes is fine.)

Answer 1

I finally found a compatible solution between Delphi and C# for AES-128. It’s also works on Wine. Here’s my Delphi code:

unit TntLXCryptoUtils;

interface

function AES128_Encrypt(Value, Password: string): string;
function AES128_Decrypt(Value, Password: string): string;

implementation

uses
  SysUtils, Windows, IdCoderMIME, TntLXUtils;

//-------------------------------------------------------------------------------------------------------------------------
//    Base64 Encode/Decode
//-------------------------------------------------------------------------------------------------------------------------

function Base64_Encode(Value: TBytes): string;
var
  Encoder: TIdEncoderMIME;
begin
  Encoder := TIdEncoderMIME.Create(nil);
  try
    Result := Encoder.EncodeBytes(Value);
  finally
    Encoder.Free;
  end;
end;

function Base64_Decode(Value: string): TBytes;
var
  Encoder: TIdDecoderMIME;
begin
  Encoder := TIdDecoderMIME.Create(nil);
  try
    Result := Encoder.DecodeBytes(Value);
  finally
    Encoder.Free;
  end;
end;

//-------------------------------------------------------------------------------------------------------------------------
//    WinCrypt.h
//-------------------------------------------------------------------------------------------------------------------------

type
  HCRYPTPROV  = Cardinal;
  HCRYPTKEY   = Cardinal;
  ALG_ID      = Cardinal;
  HCRYPTHASH  = Cardinal;

const
  _lib_ADVAPI32    = 'ADVAPI32.dll';
  CALG_SHA_256     = 32780;
  CALG_AES_128     = 26126;
  CRYPT_NEWKEYSET  = $00000008;
  PROV_RSA_AES     = 24;
  KP_MODE          = 4;
  CRYPT_MODE_CBC   = 1;

function CryptAcquireContext(var Prov: HCRYPTPROV; Container: PChar; Provider: PChar; ProvType: LongWord; Flags: LongWord): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptAcquireContextW';
function CryptDeriveKey(Prov: HCRYPTPROV; Algid: ALG_ID; BaseData: HCRYPTHASH; Flags: LongWord; var Key: HCRYPTKEY): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptDeriveKey';
function CryptSetKeyParam(hKey: HCRYPTKEY; dwParam: LongInt; pbData: PBYTE; dwFlags: LongInt): LongBool stdcall; stdcall; external _lib_ADVAPI32 name 'CryptSetKeyParam';
function CryptEncrypt(Key: HCRYPTKEY; Hash: HCRYPTHASH; Final: LongBool; Flags: LongWord; pbData: PBYTE; var Len: LongInt; BufLen: LongInt): LongBool;stdcall;external _lib_ADVAPI32 name 'CryptEncrypt';
function CryptDecrypt(Key: HCRYPTKEY; Hash: HCRYPTHASH; Final: LongBool; Flags: LongWord; pbData: PBYTE; var Len: LongInt): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptDecrypt';
function CryptCreateHash(Prov: HCRYPTPROV; Algid: ALG_ID; Key: HCRYPTKEY; Flags: LongWord; var Hash: HCRYPTHASH): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptCreateHash';
function CryptHashData(Hash: HCRYPTHASH; Data: PChar; DataLen: LongWord; Flags: LongWord): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptHashData';
function CryptReleaseContext(hProv: HCRYPTPROV; dwFlags: LongWord): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptReleaseContext';
function CryptDestroyHash(hHash: HCRYPTHASH): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptDestroyHash';
function CryptDestroyKey(hKey: HCRYPTKEY): LongBool; stdcall; external _lib_ADVAPI32 name 'CryptDestroyKey';

//-------------------------------------------------------------------------------------------------------------------------

{$WARN SYMBOL_PLATFORM OFF}

function __CryptAcquireContext(ProviderType: Integer): HCRYPTPROV;
begin
  if (not CryptAcquireContext(Result, nil, nil, ProviderType, 0)) then
  begin
    if HRESULT(GetLastError) = NTE_BAD_KEYSET then
      Win32Check(CryptAcquireContext(Result, nil, nil, ProviderType, CRYPT_NEWKEYSET))
    else
      RaiseLastOSError;
  end;
end;

function __AES128_DeriveKeyFromPassword(m_hProv: HCRYPTPROV; Password: string): HCRYPTKEY;
var
  hHash: HCRYPTHASH;
  Mode: DWORD;
begin
  Win32Check(CryptCreateHash(m_hProv, CALG_SHA_256, 0, 0, hHash));
  try
    Win32Check(CryptHashData(hHash, PChar(Password), Length(Password) * SizeOf(Char), 0));
    Win32Check(CryptDeriveKey(m_hProv, CALG_AES_128, hHash, 0, Result));
    // Wine uses a different default mode of CRYPT_MODE_EBC
    Mode := CRYPT_MODE_CBC;
    Win32Check(CryptSetKeyParam(Result, KP_MODE, Pointer(@Mode), 0));
  finally
    CryptDestroyHash(hHash);
  end;
end;

function AES128_Encrypt(Value, Password: string): string;
var
  hCProv: HCRYPTPROV;
  hKey: HCRYPTKEY;
  lul_datalen: Integer;
  lul_buflen: Integer;
  Buffer: TBytes;
begin
  Assert(Password <> '');
  if (Value = '') then
    Result := ''
  else begin
    hCProv := __CryptAcquireContext(PROV_RSA_AES);
    try
      hKey := __AES128_DeriveKeyFromPassword(hCProv, Password);
      try
        // allocate buffer space
        lul_datalen := Length(Value) * SizeOf(Char);
        Buffer := TEncoding.Unicode.GetBytes(Value + '        ');
        lul_buflen := Length(Buffer);
        // encrypt to buffer
        Win32Check(CryptEncrypt(hKey, 0, True, 0, @Buffer[0], lul_datalen, lul_buflen));
        SetLength(Buffer, lul_datalen);
        // base 64 result
        Result := Base64_Encode(Buffer);
      finally
        CryptDestroyKey(hKey);
      end;
    finally
      CryptReleaseContext(hCProv, 0);
    end;
  end;
end;

function AES128_Decrypt(Value, Password: string): string;
var
  hCProv: HCRYPTPROV;
  hKey: HCRYPTKEY;
  lul_datalen: Integer;
  Buffer: TBytes;
begin
  Assert(Password <> '');
  if Value = '' then
    Result := ''
  else begin
    hCProv := __CryptAcquireContext(PROV_RSA_AES);
    try
      hKey := __AES128_DeriveKeyFromPassword(hCProv, Password);
      try
        // decode base64
        Buffer := Base64_Decode(Value);
        // allocate buffer space
        lul_datalen := Length(Buffer);
        // decrypt buffer to to string
        Win32Check(CryptDecrypt(hKey, 0, True, 0, @Buffer[0], lul_datalen));
        Result := TEncoding.Unicode.GetString(Buffer, 0, lul_datalen);
      finally
        CryptDestroyKey(hKey);
      end;
    finally
      CryptReleaseContext(hCProv, 0);
    end;
  end;
end;

end.

And here’s my C# code:

public class TntCryptoUtils
{
    private static ICryptoTransform __Get_AES128_Transform(string password, bool AsDecryptor)
    {
        const int KEY_SIZE = 16;
        var sha256CryptoServiceProvider = new SHA256CryptoServiceProvider();
        var hash = sha256CryptoServiceProvider.ComputeHash(Encoding.Unicode.GetBytes(password));
        var key = new byte[KEY_SIZE];
        var iv = new byte[KEY_SIZE];
        Buffer.BlockCopy(hash, 0, key, 0, KEY_SIZE);
        //Buffer.BlockCopy(hash, KEY_SIZE, iv, 0, KEY_SIZE); // On the Windows side, the IV is always 0 (zero)
        //
        if (AsDecryptor)
            return new AesCryptoServiceProvider().CreateDecryptor(key, iv);
        else
            return new AesCryptoServiceProvider().CreateEncryptor(key, iv);
    }

    public static string AES128_Encrypt(string Value, string Password)
    {
        byte[] Buffer = Encoding.Unicode.GetBytes(Value);
        //
        using (ICryptoTransform transform = __Get_AES128_Transform(Password, false))
        {
            byte[] encyptedBlob = transform.TransformFinalBlock(Buffer, 0, Buffer.Length);
            return Convert.ToBase64String(encyptedBlob);
        }
    }

    public static string AES128_Decrypt(string Value, string Password)
    {
        byte[] Buffer = Convert.FromBase64String(Value);
        //
        using (ICryptoTransform transform = __Get_AES128_Transform(Password, true))
        {
            byte[] decyptedBlob = transform.TransformFinalBlock(Buffer, 0, Buffer.Length);
            return Encoding.Unicode.GetString(decyptedBlob);
        }
    }
}