secp256k1_extrakeys.h

#ifndef SECP256K1_EXTRAKEYS_H
#define SECP256K1_EXTRAKEYS_H

#include "secp256k1.h"

#ifdef __cplusplus
extern "C" {
#endif

/** Opaque data structure that holds a parsed and valid "x-only" public key.
 *  An x-only pubkey encodes a point whose Y coordinate is even. It is
 *  serialized using only its X coordinate (32 bytes). See BIP-340 for more
 *  information about x-only pubkeys.
 *
 *  The exact representation of data inside is implementation defined and not
 *  guaranteed to be portable between different platforms or versions. It is
 *  however guaranteed to be 64 bytes in size, and can be safely copied/moved.
 *  If you need to convert to a format suitable for storage, transmission, or
 *  comparison, use secp256k1_xonly_pubkey_serialize and
 *  secp256k1_xonly_pubkey_parse.
 */
typedef struct {
    unsigned char data[64];
} secp256k1_xonly_pubkey;

/** Opaque data structure that holds a keypair consisting of a secret and a
 *  public key.
 *
 *  The exact representation of data inside is implementation defined and not
 *  guaranteed to be portable between different platforms or versions. It is
 *  however guaranteed to be 96 bytes in size, and can be safely copied/moved.
 */
typedef struct {
    unsigned char data[96];
} secp256k1_keypair;

/** Parse a 32-byte sequence into a xonly_pubkey object.
 *
 *  Returns: 1 if the public key was fully valid.
 *           0 if the public key could not be parsed or is invalid.
 *
 *  Args:   ctx: a secp256k1 context object (cannot be NULL).
 *  Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to a
 *               parsed version of input. If not, it's set to an invalid value.
 *               (cannot be NULL).
 *  In: input32: pointer to a serialized xonly_pubkey (cannot be NULL)
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_parse(
    const secp256k1_context* ctx,
    secp256k1_xonly_pubkey* pubkey,
    const unsigned char *input32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** Serialize an xonly_pubkey object into a 32-byte sequence.
 *
 *  Returns: 1 always.
 *
 *  Args:     ctx: a secp256k1 context object (cannot be NULL).
 *  Out: output32: a pointer to a 32-byte array to place the serialized key in
 *                 (cannot be NULL).
 *  In:    pubkey: a pointer to a secp256k1_xonly_pubkey containing an
 *                 initialized public key (cannot be NULL).
 */
SECP256K1_API int secp256k1_xonly_pubkey_serialize(
    const secp256k1_context* ctx,
    unsigned char *output32,
    const secp256k1_xonly_pubkey* pubkey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** Converts a secp256k1_pubkey into a secp256k1_xonly_pubkey.
 *
 *  Returns: 1 if the public key was successfully converted
 *           0 otherwise
 *
 *  Args:         ctx: pointer to a context object (cannot be NULL)
 *  Out: xonly_pubkey: pointer to an x-only public key object for placing the
 *                     converted public key (cannot be NULL)
 *          pk_parity: pointer to an integer that will be set to 1 if the point
 *                     encoded by xonly_pubkey is the negation of the pubkey and
 *                     set to 0 otherwise. (can be NULL)
 *  In:        pubkey: pointer to a public key that is converted (cannot be NULL)
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_from_pubkey(
    const secp256k1_context* ctx,
    secp256k1_xonly_pubkey *xonly_pubkey,
    int *pk_parity,
    const secp256k1_pubkey *pubkey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4);

/** Tweak an x-only public key by adding the generator multiplied with tweak32
 *  to it.
 *
 *  Note that the resulting point can not in general be represented by an x-only
 *  pubkey because it may have an odd Y coordinate. Instead, the output_pubkey
 *  is a normal secp256k1_pubkey.
 *
 *  Returns: 0 if the arguments are invalid or the resulting public key would be
 *           invalid (only when the tweak is the negation of the corresponding
 *           secret key). 1 otherwise.
 *
 *  Args:           ctx: pointer to a context object initialized for verification
 *                       (cannot be NULL)
 *  Out:  output_pubkey: pointer to a public key to store the result. Will be set
 *                       to an invalid value if this function returns 0 (cannot
 *                       be NULL)
 *  In: internal_pubkey: pointer to an x-only pubkey to apply the tweak to.
 *                       (cannot be NULL).
 *              tweak32: pointer to a 32-byte tweak. If the tweak is invalid
 *                       according to secp256k1_ec_seckey_verify, this function
 *                       returns 0. For uniformly random 32-byte arrays the
 *                       chance of being invalid is negligible (around 1 in
 *                       2^128) (cannot be NULL).
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_tweak_add(
    const secp256k1_context* ctx,
    secp256k1_pubkey *output_pubkey,
    const secp256k1_xonly_pubkey *internal_pubkey,
    const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);

/** Checks that a tweaked pubkey is the result of calling
 *  secp256k1_xonly_pubkey_tweak_add with internal_pubkey and tweak32.
 *
 *  The tweaked pubkey is represented by its 32-byte x-only serialization and
 *  its pk_parity, which can both be obtained by converting the result of
 *  tweak_add to a secp256k1_xonly_pubkey.
 *
 *  Note that this alone does _not_ verify that the tweaked pubkey is a
 *  commitment. If the tweak is not chosen in a specific way, the tweaked pubkey
 *  can easily be the result of a different internal_pubkey and tweak.
 *
 *  Returns: 0 if the arguments are invalid or the tweaked pubkey is not the
 *           result of tweaking the internal_pubkey with tweak32. 1 otherwise.
 *  Args:            ctx: pointer to a context object initialized for verification
 *                       (cannot be NULL)
 *  In: tweaked_pubkey32: pointer to a serialized xonly_pubkey (cannot be NULL)
 *     tweaked_pk_parity: the parity of the tweaked pubkey (whose serialization
 *                        is passed in as tweaked_pubkey32). This must match the
 *                        pk_parity value that is returned when calling
 *                        secp256k1_xonly_pubkey with the tweaked pubkey, or
 *                        this function will fail.
 *       internal_pubkey: pointer to an x-only public key object to apply the
 *                        tweak to (cannot be NULL)
 *               tweak32: pointer to a 32-byte tweak (cannot be NULL)
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_tweak_add_check(
    const secp256k1_context* ctx,
    const unsigned char *tweaked_pubkey32,
    int tweaked_pk_parity,
    const secp256k1_xonly_pubkey *internal_pubkey,
    const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4) SECP256K1_ARG_NONNULL(5);

/** Compute the keypair for a secret key.
 *
 *  Returns: 1: secret was valid, keypair is ready to use
 *           0: secret was invalid, try again with a different secret
 *  Args:    ctx: pointer to a context object, initialized for signing (cannot be NULL)
 *  Out: keypair: pointer to the created keypair (cannot be NULL)
 *  In:   seckey: pointer to a 32-byte secret key (cannot be NULL)
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_create(
    const secp256k1_context* ctx,
    secp256k1_keypair *keypair,
    const unsigned char *seckey
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** Get the public key from a keypair.
 *
 *  Returns: 0 if the arguments are invalid. 1 otherwise.
 *  Args:    ctx: pointer to a context object (cannot be NULL)
 *  Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to
 *               the keypair public key. If not, it's set to an invalid value.
 *               (cannot be NULL)
 *  In: keypair: pointer to a keypair (cannot be NULL)
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_pub(
    const secp256k1_context* ctx,
    secp256k1_pubkey *pubkey,
    const secp256k1_keypair *keypair
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

/** Get the x-only public key from a keypair.
 *
 *  This is the same as calling secp256k1_keypair_pub and then
 *  secp256k1_xonly_pubkey_from_pubkey.
 *
 *  Returns: 0 if the arguments are invalid. 1 otherwise.
 *  Args:   ctx: pointer to a context object (cannot be NULL)
 *  Out: pubkey: pointer to an xonly_pubkey object. If 1 is returned, it is set
 *               to the keypair public key after converting it to an
 *               xonly_pubkey. If not, it's set to an invalid value (cannot be
 *               NULL).
 *    pk_parity: pointer to an integer that will be set to the pk_parity
 *               argument of secp256k1_xonly_pubkey_from_pubkey (can be NULL).
 *  In: keypair: pointer to a keypair (cannot be NULL)
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_xonly_pub(
    const secp256k1_context* ctx,
    secp256k1_xonly_pubkey *pubkey,
    int *pk_parity,
    const secp256k1_keypair *keypair
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(4);

/** Tweak a keypair by adding tweak32 to the secret key and updating the public
 *  key accordingly.
 *
 *  Calling this function and then secp256k1_keypair_pub results in the same
 *  public key as calling secp256k1_keypair_xonly_pub and then
 *  secp256k1_xonly_pubkey_tweak_add.
 *
 *  Returns: 0 if the arguments are invalid or the resulting keypair would be
 *           invalid (only when the tweak is the negation of the keypair's
 *           secret key). 1 otherwise.
 *
 *  Args:       ctx: pointer to a context object initialized for verification
 *                   (cannot be NULL)
 *  In/Out: keypair: pointer to a keypair to apply the tweak to. Will be set to
 *                   an invalid value if this function returns 0 (cannot be
 *                   NULL).
 *  In:     tweak32: pointer to a 32-byte tweak. If the tweak is invalid according
 *                   to secp256k1_ec_seckey_verify, this function returns 0. For
 *                   uniformly random 32-byte arrays the chance of being invalid
 *                   is negligible (around 1 in 2^128) (cannot be NULL).
 */
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_xonly_tweak_add(
    const secp256k1_context* ctx,
    secp256k1_keypair *keypair,
    const unsigned char *tweak32
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

#ifdef __cplusplus
}
#endif

#endif /* SECP256K1_EXTRAKEYS_H */