I am wondering if we shouldn't have a BIP32 addendum which makes the following signing related recommendations:
(1) Recommend a specific deterministic DSA derandomization procedure (a deterministic way to generate the DSA nonce), presumably one based on HMAC-SHA512 (since BIP32 uses that construct) or SHA256 in the style of RFC 6979. DSA systems being compromised due to poor randomness at runtime is not new. It effected other systems before it effected Bitcoin systems, it's not a new problem and it's not going away. It's difficult to tell if an implementation is correct or not. Use of a fully deterministic signature would allow for complete test vectors in signing and complete confidence that there is no random number related weakness in a signing implementation. In particular, with relevance to our ecosystem a maliciously modified difficult to audit hardware wallet could be leaking its keys material via its signatures. Even without producing insecure K values it could use the choice of K to leak a couple bits of an encrypted root key with every signature, and allow the malicious party to recover the keys by simply observing the network. Making the signatures deterministic would make this kind of misbehavior practically discoverable. We wouldn't be alone in making this change, in general industry is moving in this direction because it has become clear that DSA is a hazard otherwise. The primary arguments in most spaces against derandomizing DSA are FIPS conformance (irrelevant for us) and reasonable concerns about the risks of using a (less) reviewed cryptographic construct. With widespread motion towards derandomized DSA this latter concern is less of an issue. Libcrypt has also implemented derandomized DSA in git. The ed25519 signature system of DJB, et. al. also uses a similar derandomization. An alternative is implementing a still random construct where K is some H(message||key||random) which should remain secure even where the randomness is poor, but this loses the advantage of being able to externally verify that an implementation is not leaking information. OpenSSL development has implemented a form of this recently. See also: http://tools.ietf.org/rfc/rfc6979.txt (2) Recommends a procedure for using only even S values in signatures, eliminating this source of mutability in transactions. This can be accomplished via post-processing of existing signatures, but since it requires bignum math it is usually preferable to implement it along with signing. I believe someday this will become a network requirement for Bitcoin, but regardless it makes sense to implement it as a best practice sooner rather than later. Thoughts? ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite! It's a free troubleshooting tool designed for production. Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk _______________________________________________ Bitcoin-development mailing list Bitcoin-development@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bitcoin-development
