Hi,
Assumption 1 : a privacy key can become uncrackable. Assumption 2 : an individual signature can become immune to fraud. Posit : fuse the two together so that pseudonyms/aliases/online names ensure complete privacy, but ensure that you talk to the same person everytime. Probably proposed already.
Unforutnately both of your assumptions are wrong. A key cannot be 100% uncrackable, and a signature cannot be 100% immune to fraud. With electronic security, there is always a chance that a key can be cracked or a signature forged. The question is how hard is it to crack the key or forge the signature? You need to balance the security with the price. For example, a 1024-bit RSA key cannot be cracked, today, in a reasonable amount of time. However it is unclear how long that will last. Look at RSA-129; in 1977 Ron Rivest said it would take 40 quadrillion years to break the key. In 1993-4 it took 8 months (5000 MIPS-years). A key has a limited size, therefore it is theoretically possible to try every single key (this is called brute-force). Therefore it is impossible to have 100% uncrackable keys. Singatures have the same problem. Enjoy! -derek