public abstract class AsymmetricKeyExchangeFormatter { // Public Constructors public AsymmetricKeyExchangeFormatter( ); // Public Instance Properties public abstract string Parameters{get; } // Public Instance Methods public abstract byte[ ] CreateKeyExchange(byte[ ] data); public abstract byte[ ] CreateKeyExchange(byte[ ] data, Type symAlgType); public abstract void SetKey(AsymmetricAlgorithm key); }
Key exchange formatting allows a sender to encrypt a symmetric secret key value with an asymmetric algorithm and send the result to a recipient, who uses an asymmetric private key to decrypt the data. This process allows for the secure distribution of session keys, which are used with a symmetric algorithm to encrypt a single message. The secret key value is formatted prior to encryption to protect against cryptographic attack.
The abstract AsymmetricKeyExchangeFormatter class is the parent for all key exchange formatter implementations. The CreateKeyExchange( ) method uses an asymmetric public key to encrypt a symmetric secret key, expressed as a System.Byte array. The SetKey( ) method specifies the AsymmetricAlgorithm instance that contains the public key. The Parameters property returns an XML string that describes the key exchange algorithm represented by the implementation class.
The .NET Framework class library includes the RSAOAEPKeyExchangeFormatter and RSAPKCS1KeyExchangeFormatter classes, which format a secret key value using either the OAEP or PKCS #1 formatting schemes, prior to encryption with the RSA algorithm. The OAEP scheme has superseded PKCS #1, which should be used only for compatibility with legacy systems.
