"Bad Key." exception when decrypting with RSACryptoServiceProvider (C#.NET)

Question

Hello.

I am trying to decrypt data that has been encrypted previously in RSA (don't worry, I'm supposed to be able to, I have the keys. Nothing illegal :).

However, I get a "Bad Key." error at the decryption line. I am sure this key is right, as I took it from vectors. The vectors are provided in the following code. Theoretically, I have all the information to decrypt, although it won't work. I'm thinking it might be a .NET way of decrypting that I didn't understand yet.

Here is the code:

 static void Main(string[] args)
 {
  byte[] N = // Modulus
  {
   0x00, 0x8C, 0x35, 0x04, 0xC8, 0x40, 0xB3, 0x67, 0xD8, 0x42, 0x35, 0x78, 0xF6, 0x2A, 0x02, 0xBE,
   0xF7, 0x1C, 0xCD, 0x9D, 0x98, 0x55, 0x16, 0x3F, 0x81, 0xA4, 0xE5, 0x3E, 0x3D, 0x38, 0x27, 0xEE,
   0x0D, 0x8B, 0xAF, 0xB0, 0xBB, 0xBA, 0xA4, 0xE1, 0xF2, 0xB6, 0x79, 0x92, 0x5B, 0x72, 0xBA, 0xC8,
   0xD7, 0x63, 0xA9, 0x60, 0x17, 0xB1, 0x34, 0xF1, 0xA9, 0xE3, 0x46, 0x67, 0xB8, 0x06, 0x9A, 0xCD,
   0x59, 0x95, 0x10, 0x32, 0x74, 0x15, 0x73, 0xB1, 0x09, 0x43, 0x56, 0xA3, 0x0B, 0xE5, 0x6D, 0x2F,
   0x29, 0xF2, 0xB6, 0x6F, 0x5D, 0xA9, 0x55, 0x19, 0x6A, 0x2E, 0xB0, 0x30, 0x6A, 0x3F, 0xAB, 0x9F,
   0x4F, 0xCE, 0x12, 0x66, 0x28, 0xDE, 0xEB, 0x4C, 0x07, 0x9E, 0x5F, 0x24, 0x47, 0x50, 0x39, 0xB8,
   0x8F, 0x0F, 0xB8, 0x8C, 0x62, 0x8C, 0xC7, 0xA8, 0x30, 0x8C, 0xB3, 0x27, 0xA3, 0x13, 0xBC, 0xB0,
   0xA5
  };

  byte[] E = // Public exponent
  {
   0x01, 0x00, 0x01
  };   

  byte[] D = // Private key
  {
   0x0D, 0x55, 0xA9, 0x8B, 0xC6, 0x23, 0x89, 0xF7, 0xD6, 0x6C, 0x31, 0x81, 0xF0, 0x02, 0xEC, 0xD8,
   0xA1, 0xC3, 0xA8, 0x7E, 0x69, 0x71, 0x41, 0x3E, 0xFA, 0x48, 0xD7, 0x3F, 0x89, 0x4C, 0xBA, 0xE6,
   0x4C, 0xE7, 0xBB, 0xBE, 0x4F, 0x05, 0x09, 0x7C, 0x45, 0x00, 0x90, 0xFB, 0xE3, 0x90, 0x82, 0x33,
   0x82, 0x06, 0x04, 0xDE, 0x9B, 0xFA, 0xF6, 0x14, 0xFB, 0x49, 0xA1, 0xE9, 0xAD, 0xAF, 0x21, 0x62,
   0x84, 0x45, 0x3F, 0xB4, 0x6C, 0x8A, 0xFF, 0xE1, 0x8C, 0x5B, 0xC9, 0xBA, 0xD5, 0xB3, 0x48, 0x57,
   0x5A, 0xA8, 0x3F, 0x11, 0x28, 0xD3, 0xB3, 0x2F, 0xAF, 0x32, 0x29, 0xC3, 0xA4, 0x20, 0xC4, 0x03,
   0x89, 0xD4, 0x42, 0x0D, 0xAB, 0x5F, 0x06, 0x7F, 0x57, 0xBE, 0xD1, 0x90, 0x0E, 0x5E, 0x47, 0xE8,
   0xC8, 0xFF, 0xF3, 0x0F, 0xC2, 0xD1, 0x58, 0x9A, 0xEC, 0x66, 0x0B, 0x46, 0x9B, 0x79, 0x33, 0xC1
  };

  byte[] C = // Ciphertext - to be decrypted
  {
   0x70, 0x72, 0xD9, 0xAD, 0x1C, 0x7D, 0x0D, 0xDF, 0x3F, 0xC7, 0xE7, 0xF5, 0x82, 0x2D, 0x64, 0x7A,
   0xC8, 0x60, 0xC9, 0x93, 0x24, 0x14, 0x1A, 0xC3, 0xA4, 0x98, 0xB4, 0x63, 0x29, 0x5C, 0xEA, 0x41,
   0x0A, 0xC4, 0x28, 0x0D, 0xED, 0x8C, 0x53, 0x20, 0xFC, 0x6B, 0x3A, 0x13, 0xBD, 0x0C, 0x2E, 0xB6,
   0xA0, 0x19, 0xD4, 0xB5, 0xF3, 0x66, 0x1B, 0x70, 0x81, 0x3E, 0xB1, 0x68, 0x0A, 0x54, 0x23, 0x8E,
   0x65, 0xD8, 0x8E, 0xE6, 0x70, 0x56, 0xB4, 0x3A, 0x0D, 0xD6, 0xC7, 0x12, 0x3F, 0x18, 0xCD, 0x3F,
   0xE3, 0x63, 0x32, 0x6E, 0x4D, 0x7E, 0x2F, 0x4E, 0x5C, 0x6B, 0x77, 0x03, 0x37, 0x32, 0xD2, 0xF7,
   0x27, 0x2D, 0x4B, 0xD8, 0x89, 0x89, 0x23, 0xA3, 0x9A, 0xD0, 0x95, 0x38, 0xD5, 0x00, 0x4B, 0x86,
   0x46, 0x0C, 0x54, 0x4E, 0x1F, 0xAA, 0x34, 0x0D, 0x00, 0x1B, 0x38, 0x56, 0x83, 0x4F, 0x07, 0x68
  };

  byte[] M = // Cleartext - reference
  {
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   0x71, 0x77, 0x65, 0x72, 0x74, 0x79, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   0x61, 0x73, 0x64, 0x66, 0x67, 0x68, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
  };

  RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(1024);
  RSAParameters param = new RSAParameters();
  param.Exponent = E;
  param.D = D;
  param.Modulus = N; // I don't know why the modulus (public key) is needed here. we're decrypting!
  // But I get an error at importparameters if it's not there.
  rsa.ImportParameters(param);

  byte[] R = rsa.Decrypt(C, false); // Result. This decryption errors out with "Bad Key."

  Console.WriteLine(R == M); // Should be true.

  Console.Read();
 }

Any insight is greatly appreciated. I have been trying to debug this for weeks. Literally.

Answer 1

It seems importing just D is not enough. I believe you have to set all the following properties:

• Modulus
• Exponent
• Q
• DP
• DQ
• InverseQ
• D

Answer 2

I had the same problem with the "Bad Key" exception, turned out that the problem was how I was generating my certificate.

I was using the switch:

-sky signature

and when I changed it to:

-sky exchange

it worked fine.

Here is the full command I used for makecert:

makecert -r -pe -n "CN=MyName" -ss my -sr CurrentUser -sky exchange