On 27/03/13 22:13 PM, Ben Laurie wrote:
On 27 March 2013 17:20, Steven Bellovin <[email protected]> wrote:
On Mar 27, 2013, at 3:50 AM, Jeffrey Walton <[email protected]> wrote:
What is the reason for checksumming symmetric keys in ciphers like BATON?
Are symmetric keys distributed with the checksum acting as a
authentication tag? Are symmetric keys pre-tested for resilience
against, for example, chosen ciphertext and related key attacks?
The parity bits in DES were explicitly intended to guard against
ordinary transmission and memory errors.
Correct me if I'm wrong, but the parity bits in DES guard the key, which
doesn't need correcting? And the block which does need correcting has
no space for parity bits?
Note, though, that this
was in 1976, when such precautions were common. DES was intended
to be implemented in dedicated hardware, so a communications path
was needed, and hence error-checking was a really good idea.
And in those days they hadn't quite wrapped their heads around the
concept of layering?
Layering was the "big idea" of the ISO 7 layer model. From memory this
first started appearing in standards committees around 1984 or so? So
likely it was developed as a concept in the decade before then -- late
1970s to early 1980s.
That said, I used to work for a guy with a long history in comms. His
take was that the designers of each layer didn't trust the designers
of the layer below, so they added in their own error correction.
Having seen how crypto has failed lately, perhaps we should have more
of the same distrust!
It's still the same. This is why websites have a notice on them "don't
push the PAY NOW button twice!" Strict layering makes the separation
between skill specialties easier to conceptualise but it does not
necessarily make architectural sense. It works well enough if security
isn't an issue.
iang
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