[Cryptography] Trapdoor symmetric key

[ianG]

On 8/09/13 16:42 PM, Phillip Hallam-Baker wrote:
> Two caveats on the commentary about a symmetric key algorithm with a
> trapdoor being a public key algorithm.
>
> 1) The trapdoor need not be a good public key algorithm, it can be
> flawed in ways that would make it unsuited for use as a public key
> algorithm. For instance being able to compute the private key from the
> public or deduce the private key from multiple messages.
>
> 2) The trapdoor need not be a perfect decrypt. A trapdoor that reduced
> the search space for brute force search from 128 bits to 64 or only
> worked on some messages would be enough leverage for intercept purposes
> but make it useless as a public key system.


Thanks.  This far better explains the conundrum.  There is a big 
difference between a conceptual public key algorithm, and one that is 
actually good enough to compete with the ones we typically use.


iang