[bitcoin-dev] Multiparty signatures

Adam Back adam.back at gmail.com
Wed Jul 11 10:35:08 UTC 2018


On Wed, Jul 11, 2018, 02:42 Erik Aronesty via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:
> Basically you're just replacing addition with interpolation everywhere in
the musig construction

Yes, but you can't do that without a delinearization mechanism to prevent
adaptive public key choice being used to break the scheme using Wagner's
attack. It is not specific to addition, it is a generalized birthday attack.

Look at the delinearization mechanism for an intuition, all public keys are
hashed along with per value hash, so that pre-commits and forces the public
keys to be non-adaptively chosen.

Adaptively chosen public keys are dangerous and simple to exploit for
example pub keys A+B, add party C' he chooses C=C'-A-B, now we can sign for
A+B+C using adaptively chose public key C.

Btw Wagner also breaks this earlier delinearization scheme
S=H(A)*A+H(B)*B+H(C)*C

Adam
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