Flaws of PGP or GPG + Root of Trust

All systems based on cryptography work by relying on a root of trust,

something that a protocol can build security on top of.

A root of trust can be a secret or a public value

that we start the protocol with or an out-of-band channel that we can use to obtain them

A surprising flaw of PGP comes from the fact that the signing and encryption operations are composed without care.

because of this naive composition of cryptographic algorithms, one can re-encrypt a signed email they received and send that to another recipient

PGP uses

old cryptographic algorithms.

PGP does not have authenticated encryption

and is, thus, not secure if used without signatures

Due to bad PGP design, receiving a signed message

doesn’t necessarily mean we were the intended recipient.

There is no forward secrecy by default

in PGP