A new System.Security.Cryptography.HMACSHA1 instance, unless the default settings have been changed.
By default, this overload uses the System.Security.Cryptography.HMACSHA1 implementation of a keyed hash algorithm. If you want to specify a different implementation, use the KeyedHashAlgorithm.Create(string) overload, which lets you specify an algorithm name, instead. The cryptography configuration system defines the default implementation of the System.Security.Cryptography.KeyedHashAlgorithm class.