Crypto Idea; Multi-Part Sigs

[hughes@ah.com (Eric Hughes)]

>You can't have it that each of three individuals can decrypt messages
>sent to a key, while they all have to cooperate to sign messages.

You can, but the key can't be a regular RSA key.

>Generally speaking, decryption and signing are identical in the RSA
>cryptosystem.

That's right, don't use RSA as such.

Choose two RSA keys.  Make one as Hal describes for signing.  Use the
other one for receiving.  The public key in this system is a pair of
public RSA keys.  You break symmetry, and lose automatic PGP support,
but it seems to have the characteristics required.

Eric