Media signals such as audio and/or video signals are certified as being authentic. A private key and a corresponding public key are provided. For a current media segment of the media signal, a signature is created using the private key to sign data based on media content of the current media segment combined with a signature from a media segment present at another point within the media signal where the signature from the media segment present at another point within the media signal is created by signing with the private key data based on media content of the media segment present at the other point within the media signal. The signature is included in metadata of the current media segment of the media signal and the public key is included in a second metadata of the media signal.