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Update bip-schnorr.mediawiki

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Co-Authored-By: Tim Ruffing <tim@timruffing.de>
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Jonas Nick 2019-08-20 10:53:51 +00:00 • committed by GitHub
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@ -77,7 +77,7 @@ expensive conversion to affine coordinates first. This would even be the case if
For ''P'' the speed of signing and verification does not significantly differ between any of the three options because affine coordinates of the point have to computed anyway. We therefore choose the same option as for ''R''. The signing algorithm ensures that the signature is valid under the correct public key by negating the secret key if necessary.
It is important to not mix up the 32-byte bip-schnorr public key format and other existing public key formats (e.g. encodings used in Bitcoin's ECDSA). Concretely, a verifier should only accept 32 byte public keys and not, for example, convert a 33 byte public key by throwing away the first byte. Otherwise, two public keys would be valid for a single signature which can result in subtle malleability issues (although this type of malleability already exists in the case of ECDSA signatures).
It is important to not mix up the 32-byte bip-schnorr public key format and other existing public key formats (e.g. encodings used in Bitcoin's ECDSA). Concretely, a verifier should only accept 32-byte public keys and not, for example, convert a 33-byte public key by throwing away the first byte. Otherwise, two public keys would be valid for a single signature which can result in subtle malleability issues (although this type of malleability already exists in the case of ECDSA signatures).
Implicit Y coordinates are not a reduction in security when expressed as the number of elliptic curve operations an attacker is expected to perform to compute the secret key. An attacker can normalize any given public key to a point whose Y coordinate is a quadratic residue by negating the point if necessary. This is just a subtraction of field elements and not an elliptic curve operation.