4

What are the problems related in using the "normal" ( bigger than N/2) value of the s number in transaction signature and why we use the lower one? Is it about the math behind the ecdsa?

1 Answer 1

2

Details are in BIP 146:

We require that the S value inside ECDSA signatures is at most the curve order divided by 2...

...

A high S value in signature could be trivially replaced by S' = 0xFFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFE BAAEDCE6 AF48A03B BFD25E8C D0364141 - S.

Signatures encode two important values for verification r and S. If (r, S) is a valid signature, then so is (r, -S), which is equivalent to (r, curver_order -S).

2
  • Maybe I've understood. Before BIP 146, a relay node could invalidate my trx using the higher s value, which is mathematically equals, but it would have result in a completely different trx hash. So low-s value is a care for the trx malleability?
    – dc_Bita98
    Apr 9, 2019 at 14:26
  • 1
    Yes, both transactions would be valid, but with different signatures and TX hash. Yes, it's against TX (and TXID) malleability @dc_Bita98
    – MCCCS
    Apr 9, 2019 at 15:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.