I have unsubscribed from this mailing list. Please remove my name from your personal address lists. Thanks. ahg3 ---------- From: Jeff Barber[SMTP:jeffb@sware.com] Sent: Tuesday, October 24, 1995 4:05 PM To: RobertW.Baldwin Cc: cypherpunks Subject: Re: 80 bit security from 40 bit exportable products baldwin writes:
Long ago vendors should have put encryption into network layer products, but for a variety of reasons that effort was delayed or discouraged. One effect of this lack is that almost every layer of the network stack is adding its own encryption. For example, the HTTP session layer added S-HTTP and the TCP transport layer added SSL. Soon we will have network layer encryption with IPsec. The vendors for each layer can export a product that uses ciphers with 40 bit keys. A user can then combine multiple products to get more than 40 bits worth of security. For example, a web client might fetch an S-HTTP page over an SSL protected link via a firewall that supports IPsec tunnels. That's three 40 bit keys protecting the data over the internet link (of course, this may not be equivalent to a 120 bit cipher, that depends on the details of the cipher systems and independence of the key setups). Interesting possibilities. --Bob Baldwin
Even if you assume complete independence of key setup, if a successful decryption at each layer can be independently detected and verified (which seems likely in your example), there're only about 3 * (2 ^ 40) total operations in the worst case, NOT 2 ^ (3 * 40) operations needed to expose the plaintext. This is an effective 41.5 bits, not 120. -- Jeff