RSAOAEPKeyExchangeFormatter Class

Definition

Namespace:

System.Security.Cryptography

Assemblies:

netstandard.dll, System.Security.Cryptography.dll

Source:

RSAOAEPKeyExchangeFormatter.cs

Creates Optimal Asymmetric Encryption Padding (OAEP) key exchange data using RSA.

C#

public class RSAOAEPKeyExchangeFormatter : System.Security.Cryptography.AsymmetricKeyExchangeFormatter

Inheritance

Object

AsymmetricKeyExchangeFormatter

RSAOAEPKeyExchangeFormatter

Examples

The following example shows how to use the RSAOAEPKeyExchangeFormatter class to create an exchange key for a message recipient.

C#

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

class Alice
{
    public static void Main(string[] args)
    {
        using (Bob bob = new Bob())
        {
            using (RSACryptoServiceProvider rsaKey = new RSACryptoServiceProvider())
            {
                // Get Bob's public key
                rsaKey.ImportCspBlob(bob.key);
                byte[] encryptedSessionKey = null;
                byte[] encryptedMessage = null;
                byte[] iv = null;
                Send(rsaKey, "Secret message", out iv, out encryptedSessionKey, out encryptedMessage);
                bob.Receive(iv, encryptedSessionKey, encryptedMessage);
            }
        }
    }

    private static void Send(RSA key, string secretMessage, out byte[] iv, out byte[] encryptedSessionKey, out byte[] encryptedMessage)
    {
        using (Aes aes = new AesCryptoServiceProvider())
        {
            iv = aes.IV;

            // Encrypt the session key
            RSAOAEPKeyExchangeFormatter keyFormatter = new RSAOAEPKeyExchangeFormatter(key);
            encryptedSessionKey = keyFormatter.CreateKeyExchange(aes.Key, typeof(Aes));

            // Encrypt the message
            using (MemoryStream ciphertext = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(ciphertext, aes.CreateEncryptor(), CryptoStreamMode.Write))
            {
                byte[] plaintextMessage = Encoding.UTF8.GetBytes(secretMessage);
                cs.Write(plaintextMessage, 0, plaintextMessage.Length);
                cs.Close();

                encryptedMessage = ciphertext.ToArray();
            }
        }
    }
}
public class Bob : IDisposable
{
    public byte[] key;
    private RSACryptoServiceProvider rsaKey = new RSACryptoServiceProvider();
    public Bob()
    {
        key = rsaKey.ExportCspBlob(false);
    }
    public void Receive(byte[] iv, byte[] encryptedSessionKey, byte[] encryptedMessage)
    {

        using (Aes aes = new AesCryptoServiceProvider())
        {
            aes.IV = iv;

            // Decrypt the session key
            RSAOAEPKeyExchangeDeformatter keyDeformatter = new RSAOAEPKeyExchangeDeformatter(rsaKey);
            aes.Key = keyDeformatter.DecryptKeyExchange(encryptedSessionKey);

            // Decrypt the message
            using (MemoryStream plaintext = new MemoryStream())
            using (CryptoStream cs = new CryptoStream(plaintext, aes.CreateDecryptor(), CryptoStreamMode.Write))
            {
                cs.Write(encryptedMessage, 0, encryptedMessage.Length);
                cs.Close();

                string message = Encoding.UTF8.GetString(plaintext.ToArray());
                Console.WriteLine(message);
            }
        }
    }
    public void Dispose()
    {
        rsaKey.Dispose();
    }
}

Remarks

Key exchange allows a sender to create secret information, for example, random data that can be used as a key in a symmetric encryption algorithm, and use encryption to send it to the intended recipient.

Use RSAOAEPKeyExchangeDeformatter to receive the key exchange and extract the secret information from it.

Caution

It is highly recommended that you not attempt to create your own key exchange method from the basic functionality provided, because many details of the operation must be performed carefully in order for the key exchange to be successful.

Constructors

RSAOAEPKeyExchangeFormatter()	Initializes a new instance of the RSAOAEPKeyExchangeFormatter class.
RSAOAEPKeyExchangeFormatter(AsymmetricAlgorithm)	Initializes a new instance of the RSAOAEPKeyExchangeFormatter class with the specified key.

Properties

Parameter	Gets or sets the parameter used to create padding in the key exchange creation process.
Parameters	Gets the parameters for the Optimal Asymmetric Encryption Padding (OAEP) key exchange.
Rng	Gets or sets the random number generator algorithm to use in the creation of the key exchange.

Methods

CreateKeyExchange(Byte[], Type)	Creates the encrypted key exchange data from the specified input data.
CreateKeyExchange(Byte[])	Creates the encrypted key exchange data from the specified input data.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
SetKey(AsymmetricAlgorithm)	Sets the public key to use for encrypting the key exchange data.
ToString()	Returns a string that represents the current object. (Inherited from Object)

Applies to

See also

• Cryptographic Services