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

Question

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.

Exenterate

Note: I know the modulus is 129 bytes long. The first byte is blank for some reason. Removing this byte doesn't affect the result (and that's normal, since theoretically, you don't need the modulus in the decryption process, since it's the public key.) – Exenterate

Answer 1

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

Fredette

I was getting lost in the biggest fracking rabbit hole until I found this post. Thanks for sharing!! – Beauvais

Answer 2

I see this is an old question, but am answering because it was suggested to me as an answer to a current problem.

The predicates are flawed because (a) RSA encryption doesn't work when the plain text is the same size as the key, and (b) the final comparison uses '==' to test object equality rather than element-wise equivalence.

But, the answers are good: make sure that the certificate was created such that it is good for 'exchange,' and when comparing a byte array like this, ensure element-wise equivalence.

Mandamandaean

Answer 3

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

Haydon