Digital signature are implemented using cryptography . Digital signatures can also provide acknowledgement , meaning that the signer can not successfully claim they did not sign a message , while also claiming their private key remains secret ; Digital signatures can also provide non-repudiation , meaning that the signer can not successfully claim they did not sign a message , while also claiming their private key remains secret ; further , some non-repudiation schemes offer a time stamp for the digital signature , so that even if the private key is exposed , the signature is valid nonetheless .