Class XOnlyPubKey

src/pubkey.h:227–296

};

class XOnlyPubKey
{
private:
    uint256 m_keydata;

public:
    /** Construct an empty x-only pubkey. */
    XOnlyPubKey() = default;

    XOnlyPubKey(const XOnlyPubKey&) = default;
    XOnlyPubKey& operator=(const XOnlyPubKey&) = default;

    /** Determine if this pubkey is fully valid. This is true for approximately 50% of all
     *  possible 32-byte arrays. If false, VerifySchnorr, CheckTapTweak and CreateTapTweak
     *  will always fail. */
    bool IsFullyValid() const;

    /** Test whether this is the 0 key (the result of default construction). This implies
     *  !IsFullyValid(). */
    bool IsNull() const { return m_keydata.IsNull(); }

    /** Construct an x-only pubkey from exactly 32 bytes. */
    explicit XOnlyPubKey(Span<const unsigned char> bytes);

    /** Construct an x-only pubkey from a normal pubkey. */
    explicit XOnlyPubKey(const CPubKey& pubkey) : XOnlyPubKey(Span{pubkey}.subspan(1, 32)) {}

    /** Verify a Schnorr signature against this public key.
     *
     * sigbytes must be exactly 64 bytes.
     */
    bool VerifySchnorr(const Span<const unsigned char> msg, Span<const unsigned char> sigbytes) const;

    // ELEMENTS: this is preserved from an old version of the Taproot code for use in OP_TWEAKVERIFY
    bool CheckPayToContract(const XOnlyPubKey& base, const uint256& hash, bool parity) const;

    /** Compute the Taproot tweak as specified in BIP341, with *this as internal
     * key:
     *  - if merkle_root == nullptr: H_TapTweak(xonly_pubkey)
     *  - otherwise:                 H_TapTweak(xonly_pubkey || *merkle_root)
     *
     * Note that the behavior of this function with merkle_root != nullptr is
     * consensus critical.
     */
    uint256 ComputeTapTweakHash(const uint256* merkle_root) const;

    /** Verify that this is a Taproot tweaked output point, against a specified internal key,
     *  Merkle root, and parity. */
    bool CheckTapTweak(const XOnlyPubKey& internal, const uint256& merkle_root, bool parity) const;

    /** Construct a Taproot tweaked output point with this point as internal key. */
    std::optional<std::pair<XOnlyPubKey, bool>> CreateTapTweak(const uint256* merkle_root) const;

    /** Returns a list of CKeyIDs for the CPubKeys that could have been used to create this XOnlyPubKey.
     * This is needed for key lookups since keys are indexed by CKeyID.
     */
    std::vector<CKeyID> GetKeyIDs() const;