Remove public key from secret key

[Peter Lebbing]

Ivan Peev wrote:
> Is there a way to export the secret key without the public key or remove
> the public key from exported secret key? I'm trying the following scenario:
> 
> 1. Encrypt data with particular public key on one machine.
> 2. Decrypt data with related secret key on another machine.
> 
> Basically I don't want someone to be able to generate data, which can be
> decrypted with the related secret key.

At least with RSA, the public key can be computed with just the secret key.
So it would never be cryptographically secure, it only takes some effort on
the part of the attacker to break the scheme.

I obviously don't know your exact requirements, but instead of trying to
make something designed to be public private, perhaps this will accomplish
your goal:

Create two keypairs, A and B.

The machine mentioned under point 1. above has the public key of keypair A
and the private key of keypair B.

The machine mentioned under point 2. has the private key A and public key B.

The program encrypting on machine 1. encrypts to key A and signs with key B.

The program decrypting on machine 2. only accepts data encrypted to key A
and /signed with key B/.

Now someone with access to the keyring on machine 2. cannot create encrypted
data that is accepted by the decryption program, because he cannot sign it
with key B.

HTH,

Peter Lebbing.

-- 
I'm using the GNU Privacy Guard (GnuPG) in combination with Enigmail.
You can send me encrypted mail if you want some privacy.
My key is available at http://wwwhome.ewi.utwente.nl/~lebbing/pubkey.txt