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X-only Public Key

cryptography
bitcoin

A 32-byte public key format that stores only the x-coordinate, used by BIP340 Schnorr signatures and Taproot.

1
definition

An x-only public key omits the usual prefix byte that identifies which y-coordinate parity belongs to the elliptic curve point. BIP340 defines verification rules so the missing parity is handled consistently.

2
use

X-only keys simplify Taproot and Schnorr constructions and save a small amount of space. Wallets and libraries must still handle key tweaking and parity correctly to produce valid signatures.

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