public-key: the wrong model for email?

[Ben Laurie]

Ed Gerck wrote:
> Ben Laurie wrote:
> 
>> Ed Gerck wrote:
>>
>>> If the recipient cannot in good faith detect a key-access ware, or a
>>> GAK-ware, or a Trojan, or a bug, why would a complete background
>>> check of the recipient help?
>>
>>
>> Let's assume for a moment that a solution exists that satisfies your 
>> requirements. Since the recipient _must_ be able to read the document 
>> in the end, and is assumed to be incapable of securing their software, 
>> then the document is still available to third parties without the 
>> consent of the sender, is it not?
> 
> 
> The recipient was not assumed to be entirely incapable of securing his
> software. The recipient can be trusted to do a number of things that are
> basic, for example, to operate an email software. In fact, we can even
> assume a pretty sophisticated recipient, trained to use all the security
> email software systems commercially available. Still, the recipient will
> be incapable of verifying whether his RSA private-key is weak or not. Thus,
> even fully unwillingly and under best efforts, the recipient can put the
> sender's message security at risk when using that recipient's RSA public-
> key.

Since they are using good software, the key is known to be strong, surely?

>> It seems to me that fixing the PK "problem" would in no way improve 
>> the senders situation given that threat model.
> 
> The sender's situation can be improved mostly when the sender trusts the
> least possible (ideally, nothing) regarding message security. In other
> words, the sender would like to avoid anything that is not under control or
> cannot be directly verified by the sender. Doing a background check of the
> recipient is orthogonal to the PK problem. It does not help nor solve it.

I didn't suggest a background check would help. I am suggesting that if 
you cannot rely on the recipient (or their machine) to manage keys 
properly, then you also cannot rely on them to manage decrypted emails 
properly.

Cheers,

Ben.

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