I took a quick look at your implementation of ECDSA and I think it has a bug at line 311 [1]. It looks like I could bypass the check if r or s is negative.

One thing that I don't understand is why big integer libraries developed exclusively for crypto need negative numbers. The library [2] that I contribute to doesn't need them, and it works just fine. Actually I could argue that having only non-negative numbers make it simpler and faster.

[1] https://github.com/cryptocoinjs/ecdsa/blob/master/lib/ecdsa.... [2] https://code.google.com/p/end-to-end/source/browse/javascrip...