You can have an encryption system that can only be broken by the 'right' people. We already have crypto systems where any 1 of n people can decrypt the message. If you embed a public key into the algorithm, then only the algorithm's designers would know the private key needed for decryption.

Doing this in a non-obvious way seems much more difficult, but if the NSA did have a weakness to DES, it could very possibly require knowing a secret key.