A method for transmitting digital data to a recipient via a communications network includes providing digital data and digitally signing the digital data using N cryptographic keys. Each of the N cryptographic keys is associated with a same sender of the digital data, and N>1. The recipient receives the digital data and verifies the digital signature using N cryptographic keys associated with the N cryptographic keys used to sign the digital data. In dependence upon verifying the digital signature, the recipient accepts the digital data as being authentic.