class procedure TCryptoProCSPVeryfier.DecryptFile(const SourceFile, DestFile, Password: string);
const
  BUF_LEN = 100;
  KEY_LEN = 256;
  IV_LEN = 8;
  ReadIV = True;
  // PasswordFile = 'C:\Users\Ilya\Temp\Новая папка (2)\KEY_Exported_Test_2016.01.01.dat';
var
  InStream: TFileStream;
  OutStream: TFileStream;

  Buffer: PByte;

  Key: TJwCryptKeyEx;
  BufferSize: Cardinal;
  CSP: TJwCryptProviderEx;
  Hash: TJwHashEx;
  IV: PByte;
  _PasswordFile:string;
begin

  InStream := TFileStream.Create(SourceFile, fmOpenRead);
  OutStream := TFileStream.Create(DestFile, fmCreate);
  try

    CSP := CreateCSP('', []);
    try
      Hash := TJwHashEx.Create(ALG_GOST3411, CSP);
      try
        Hash.HashData(PChar(Password), Length(Password) * SizeOf(Char));

        // создание ключа сессии
        Key := TJwCryptKeyEx.Derive(CSP, CALG_G28147, [kfExportable], KEY_LEN, Hash);
        try
          IV := nil;
          GetMem(IV, IV_LEN);
          ZeroMemory(IV, IV_LEN);
          try
            // чтение вектора инициализации
            if ReadIV then
              InStream.Read(IV^, IV_LEN);
            Key.SetIV(IV);
            GetMem(Buffer, InStream.Size - InStream.Position);
            try

              // Установка вектора инициализации
              // без него первые 8 байт расшифруются неправильно

              BufferSize := InStream.Read(Buffer^, InStream.Size - InStream.Position);

              Key.Decrypt(nil, True, [], Buffer, BufferSize);
              OutStream.Write(Buffer^, BufferSize);
            finally
              FreeMem(Buffer);
            end;
          finally
            FreeMem(IV);
          end;
        finally
          Key.Free;
        end;
      finally
        Hash.Free;
      end;
    finally
      CSP.Free;
    end;
  finally
    InStream.Free;
    OutStream.Free;
  end;
end;