SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust Leurent, G and Peyrin, T (2020) https://eprint.iacr.org/2020/014.pdf Unix, Win, Mac https://www.gnupg.org/download/index.html Simple https://github.com/filosottile/age Email https://www.thunderbird.net/