Re: [dnsext] New Version Notification for draft-mcgrew-tss-02 (fwd)

[David McGrew <[e-mail]>]

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Hi Mike,
> Hi Alfred -
> A better scheme for threshold signing for the root might be the  
> Shoup paper: "Practical Threshold Signatures", Victor Shoup ([e-mail] 
> ), IBM Research Paper RZ3121, 4/30/99
> The major difference between the two is that the Shamir system  
> (which you describe) requires the base secret (private key) be  
> reconstituted (by a trusted entity) before it can be used, where the  
> Shoup system allows partial signatures with a public gather  
> function.  E.g. In a 3 of 5 system, each of the 3 key share holders  
> partial-sign the data using their share of the private key and send  
> it (as public data) to a central location where a gather function is  
> used to form the actual signature.
I agree that threshold signatures have nice security properties, and  
that Shoup's PTS method looks good, especially because its signature- 
share generation step does not require any interaction between the  
signers.

As you say, the TSS draft lacks the partial-signature capability, but  
TSS does have the benefit of simplicity.
> Shamir is nice in that it can be used for any set of key bits. But  
> the reconstitution requirement is a point of weakness where the  
> actual private key may be compromised. The Shoup system is only  
> specified for RSA as far as I know.
Shoup's PTS method requires the use of a trusted dealer to generate  
the private keys of all of the signers.   So while it eliminates the  
need for a trusted dealer during the signing step, it does not  
eliminate that need entirely.  (At least this is the case for the  
paper that you cited above; if there is work that eliminates the  
trusted dealer, I would be very interested to see it.)

best regards,

David




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