At 10:14 AM 1/7/2004 -0500, Jerrold Leichter wrote:
Now that we've trashed non-repudiation ... just how is it different from
authentication?  In both cases, there is a clear technical meaning (though as
with anything in mathematics, when you get right down to it, the details are
complex and may be important):  To produce an authenticator/non-repudiable
signature, you must have access to the secret.  There isn't, at this level,
even any difference between the requirements for the two.  Where we get into
trouble is in attempting to bind the real world to the mathematics.  In each
case, the receiver wants to be able to say:

lets say they are somewhat different threat models (but may have some partial overlap).

it would be possible to give a dozen people the same passprhase and have some degree of confidence that only the permitted entities entitled to do something were authenticated. however, if one of them claimed that they didn't do some specific thing ... there would be difficult to differentiate between the different entities as to which entity had been authenticated at any specific time. some of the best practices security guidelines for authentication (like not sharing passwords) have more to do with non-repudiation ... than straight authentication.

key-escrow can be considered mandatory for encryption keys under the non-single-point-of-failure and availability best practices. At the same time there may be mandatory requirements for NOT having key-escrow for authentication keys under non-repudiation best practices (even when the cryptographic technology is identical ... the issue of key-escrow policy is exactly opposite depending on whether the business use is encryption of authentication).

a straight-forward authentication issue might be whether a particular message originated from a specific entity. That would not necessarily include the sense that the entity agreed with the terms and conditions described in the body of the message (say a financial transaction). This is somewhat akin to various EULA agreements that have people clicking on various buttons .... which is not an issue of authentication but of agreement; aka *repudiation* can include things that are outside the scope of authentication (not whether the message originated from me ... but do i fully agree with what is included in the body of the message). neither identification nor authentication by itself can necessarily include the concept of agreement. repudiation can include a number of items outside the sense of identification and authentication (like aggreement).

Anne & Lynn Wheeler
Internet trivia 20th anv

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