RSAOAEPKeyExchangeFormatter Class
Updated: March 2011
Creates Optimal Asymmetric Encryption Padding (OAEP) key exchange data using RSA.
Assembly: mscorlib (in mscorlib.dll)
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: |
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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. |
The following example shows how to use the RSAOAEPKeyExchangeFormatter class to create an exchange key for a message recipient.
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(); } }
System.Security.Cryptography.AsymmetricKeyExchangeFormatter
System.Security.Cryptography.RSAOAEPKeyExchangeFormatter
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
