Digital signature forgery
In a cryptographic digital signature or MAC system, digital signature forgery is the ability to create a pair consisting of a message, m {\displaystyle m} , and a signature (or MAC), σ {\displaystyle \sigma } , that is valid for m {\displaystyle m} , but has not been created in the past by the legitimate signer. There are different types of forgery.
Source: Wikipedia — Digital signature forgery (CC BY-SA 4.0)