PQ stands for Post-Quantum.
All existing messengers use RSA for key exchange.
Today it is unreliable due to the emergence of quantum computers.
According to NIST Post-Quantum Project (https://csrc.nist.gov/projects/post-quantum-cryptography
) "…sufficiently large quantum computers will be built to break essentially all public key schemes currently in use."
The importance of the problem is visible by the fact that NIST held the First PQC Standardization Conference in April 2018.
In this report (https://csrc.nist.gov/Presentations/2018/PostQuantum-RSA
) we can read:
RSA has tons of mathematical structures and a.
long history of many scary RSA security breaches.
But users keep using RSA.
RSA-512 publicly broken:
"Let's use RSA-768."
RSA-768 publicly broken:
"Let's use RSA-1024."
RSA-2048 publicly broken by quantum computers:
"Yeah, NSA already told us to use RSA-3072."
Vernam IM does not use RSA, so it is fully PQ ready.