feat: Low-s normalization for ecdsa secp256r1 signing (cosmos#9738) (c…

…osmos#9793)

* added low-s normalization to ecdsa secp256r1 signing

* go fmt fixes

* removed else block as golint required

* implement raw signature encoding for secp256r1

* move the creation of signature to after the check for sig string length

* fake commit to re-run checks? (move the creation of signature to after the check for sig string length)

* added a signature test for high s signature that requires sig validation to fail after the valid signature was mutated by extracting and scalar negating its s value

* reordered code to prevent mutated message from being used in sig verify

* added test for successful high_s signature with the ecdsa portion of the publicKey

* Remove comment for self-explanatory code.

Co-authored-by: Robert Zaremba <[email protected]>

* Missing quote

Co-authored-by: Robert Zaremba <[email protected]>

* Apply minor suggestions from code review

Co-authored-by: Robert Zaremba <[email protected]>

* normalize comments for godoc

* refactored p256Order functions as private vars

* Div -> Rsh optimizing time for division

* resolve two code coverage issues; fix some small review issues

* test using private signatureRaw function instead of copying code. Added tests to improve code coverage

Co-authored-by: Aaron Craelius <[email protected]>
Co-authored-by: Robert Zaremba <[email protected]>
Co-authored-by: Aleksandr Bezobchuk <[email protected]>
(cherry picked from commit aa37ae9)

Co-authored-by: John Kemp <[email protected]>

crypto/keys/internal/ecdsa/privkey.go

@@ -12,7 +12,13 @@ import (
 // p256Order returns the curve order for the secp256r1 curve
 // NOTE: this is specific to the secp256r1/P256 curve,
 // and not taken from the domain params for the key itself
-// (which would be a more generic approach for all EC).
+// (which would be a more generic approach for all EC)
+// In *here* we don't need to do it as a method on the key
+// since this code is only called for secp256r1
+// if called on a key:
+// func (sk PrivKey) pCurveOrder() *.big.Int {
+//     return sk.Curve.Params().N
+// }
 var p256Order = elliptic.P256().Params().N
 
 // p256HalfOrder returns half the curve order