The content integrity service allows an originator to provide proof that the content of a single message has not been modified. As mentioned previously, content integrity is meaningless to a user without origin authentication. Content integrity, on its own, authenticates the content of a message; however, the message may have been submitted by an imposter. Origin authentication, on its own, verifies the identity of message originator; however, the content received may not match the content originated. Thus, content integrity and origin authentication are provided by the same security mechanisms. These mechanisms, the content integrity check and the message origin authentication check, are described in section 11.6.3.