If Bob wants to send Alice “Hello, how are you?” the plain text would be signed with Bob’s general private key that could be verified with Bob’s general public key. This would allow Alice to forward this message to anyone while they could still verify it did indeed came from Bob.

The plain text and signature is then encrypted with one of Alice’s public keys, so only Alice could decrypt it to see the message and signature. This may be a thread specific key pair for Alice so they’re not re-using same keys between different threads.

The encrypted message is then again signed by Bob, using one of Bob’s private key, so that Alice can know the encrypted message has not been altered. This here could also be the thread specific key as noted above.

If Alice were to report Bob, Alice will need to include both the plaintext and the internal signature. This way the internally signed message could be reviewed if the plaintext and signature were forwarded to moderation for review by Charlie (just need to verify the signature against plaintext with Bob’s public key), while the exchange should be secure to only Alice and Bob.

Et voila!