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CryptoSys PKI C# Interface
The .NET Class Library for the CryptoSys PKI provides a safe, clean interface to .NET methods. These can be used in an almost identical manner in both C# and VB.NET projects. For more details see .NET Class Library Interface.
Here is a possible method to encrypt some data given the recipient's X.509 certificate.
public static byte[] RsaEncryptBytes(byte[] inputData, string certFile)
{
StringBuilder sbPublicKey;
byte[] block;
byte[] outputData;
int klen;
// 1. Read the public key from the recipient's X.509 certificate
sbPublicKey = Rsa.GetPublicKeyFromCert(certFile);
if (sbPublicKey.Length == 0)
{
Console.WriteLine("ERROR reading certificate");
return new byte[0];
}
// 2. Make an RSA data block of same length in bytes as key
// using EME-PKCS1-v1_5 encoding
klen = Rsa.KeyBytes(sbPublicKey.ToString());
if (klen <= 0)
{
Console.WriteLine("ERROR: invalid public key");
return new byte[0];
}
block = Rsa.EncodeMsg(klen, inputData, Rsa.EncodeFor.Encryption);
// 3. Encrypt with RSA public key
outputData = Rsa.RawPublic(block, sbPublicKey.ToString());
if (outputData.Length == 0)
{
Console.WriteLine("ERROR: failed to encrypt");
return new byte[0];
}
// 4. Clean up
Wipe.Data(block);
Wipe.String(sbPublicKey);
// 5. Output "ciphertext"
return outputData;
}
This could be called like this
byte[] inputData = System.Text.Encoding.Default.GetBytes("Hello world!");
string certFile = "BobRSASignByCarl.cer";
// Output: byte array of "ciphertext"
byte[] outputData = RsaEncryptBytes(inputData, certFile);
// Display output in hex format
Console.WriteLine("ENC={0}", Cnv.ToHex(outputData));
To decrypt, we could do this:
public static byte[] RsaDecryptBytes(byte[] inputData, string priKeyFile, string password)
{
StringBuilder sbPrivateKey;
byte[] block;
byte[] outputData;
// 1. Read in the private key from the encrypted key file
sbPrivateKey = Rsa.ReadEncPrivateKey(priKeyFile, password);
if (sbPrivateKey.ToString().Length == 0)
{
Console.WriteLine("ERROR reading private key file");
return new byte[0];
}
// 2. Decrypt with private key
block = Rsa.RawPrivate(inputData, sbPrivateKey.ToString());
if (block.Length == 0)
{
Console.WriteLine("Decryption error");
return new byte[0];
}
// 3. Extract the message from the encryption block
outputData = Rsa.DecodeMsg(block, Rsa.EncodeFor.Encryption);
if (outputData.Length == 0)
{
Console.WriteLine("Decryption error");
return new byte[0];
}
// 4. Clean up - NB should do this on error, too.
Wipe.Data(block);
Wipe.String(sbPrivateKey);
// 5. Output "plaintext"
return outputData;
}
Download the full source code that demonstrates this encryption and decryption, as well as methods
to carry out signing and verification in
RsaExample.cs
(zipped version, 3 kB).
To compile, add this item to a new C# Console Application project and create a reference to
diCrSysPKINet.dll.
The test certficates and private key files used in the example are in
pkiCsharpTestFiles.zip.
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This page last updated 10 September 2025.
