Question

I’ve been trying to encrypt a password with a public RSA key that is sent to me by the server.

var csp = new CspParameters(1, "Microsoft Strong Cryptographic Provider");
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(1280, csp);
byte[] key = ByteUtils.HexToBytes(client.RSAKey);
RSA.ImportCspBlob(key);
byte[] encrypted = RSA.Encrypt(Encoding.ASCII.GetBytes(password), true);

The hex key is provided in such format:

string key = "30819D300D06092A864886F70D010101050003818B0030818702818100C7BD672D8C634D443840AD809790852770D3A2E99F456D6516329E0205D0645C23FD001D4D070CEE368A20526FEB2402358C915D7E86102B1659AA8651C449C344599F72BE904B8E338E7002E9978453C5BBCCA51AC165AA265069E0EAB1411D11A2FFDD35E5A8296A6A2AF238945874E8206979B0A16E2E4260A161CAB5C905020111";

As the string is 320-bytes long in hex format, I assume the key is 160 bytes (RSA 1280)
Using this method, the provider keeps saying “Bad Version of provider.\r\n”.
I’ve tried several methods, convert it to Base64, simply import it as ASCII / Unicode. Nothing worked so far.

EDIT: My HexToBytes function (which works afaik, it returns me correct 160-b array):

public static byte[] HexToBytes(string pValue)
        {
            // FIRST. Use StringBuilder.
            StringBuilder builder = new StringBuilder();

            // SECOND... USE STRINGBUILDER!... and LINQ.
            foreach (char c in pValue.Where(IsHexDigit).Select(Char.ToUpper))
            {
                builder.Append(c);
            }

            // THIRD. If you have an odd number of characters, something is very wrong.
            string hexString = builder.ToString();
            if (hexString.Length % 2 == 1)
            {
                //throw new InvalidOperationException("There is an odd number of hexadecimal digits in this string.");
                // I will just add a zero to the end, who cares (0 padding)
                Log.WriteLine(LogLevel.Debug, "Hexstring had an odd number of hexadecimal digits.");
                hexString += '0';
            }

            byte[] bytes = new byte[hexString.Length / 2];
            // FOURTH. Use the for-loop like a pro :D
            for (int i = 0, j = 0; i < bytes.Length; i++, j += 2)
            {
                string byteString = String.Concat(hexString[j], hexString[j + 1]);
                bytes[i] = HexToByte(byteString);
            }
            return bytes;
        }

Answer 1

Your public key is not in the correct format. It is not a CSP blob. It is a DER encoded SubjectPublicKeyInfo structure. You can find source code to parse it or you can write your own. Here is one example of such code.