80 bit security from 40 bit exportable products

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

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

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> 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).

C'mon Bob.. how long has it been since you picked a lock? :-)

Given the likely presence of known or verifiable plaintext at each
nesting level, a three-deep nesting of 40-bit ciphers like this
probably increases the strength to about, ohh, a 42 bit cipher.

						- Bill


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