I would like to know the practical limitations to contact chaining multiple peoples pgp key's in order to protect a file.
In normal public key cryptography, four keys are required, public and private from both parties. But, if the integrity of one of participants is compromised say, through torture or some other form of coercion the information may as well be in plaintext.
However, what if that burden was lightened by having cryptography that required multiple keys from different individuals in order to encrypt and could be decrypted, using the public keys from those individuals. That way, it might be akin to having 2 or more deadbolts on a door that a thief would have to mitigate. I'm not talking here about encrypting a file that has already been encrypted, but using a combination of keys in order to encrypt a file that could then be decrypted only by having the public keys of everyone who did the initial encryption.
I'm sure there are a few needless redundancies or other things I'm not taking into account in this plan. What are they?