fn check_symmetric_encryption(msg: &Message<'_>) -> Result<(), &'static str>Expand description
Returns Ok(()) if we want to try symmetrically decrypting the message, and Err with a reason if symmetric decryption should not be tried.
A DOS attacker could send a message with a lot of encrypted session keys, all of which use a very hard-to-compute string2key algorithm. We would then try to decrypt all of the encrypted session keys with all of the known shared secrets. In order to prevent this, we do not try to symmetrically decrypt messages that use a string2key algorithm other than ‘Salted’.