183 lines
7.6 KiB
C
183 lines
7.6 KiB
C
#ifndef SECP256K1_SCHNORRSIG_H
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#define SECP256K1_SCHNORRSIG_H
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#include "secp256k1.h"
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#include "secp256k1_extrakeys.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/** This module implements a variant of Schnorr signatures compliant with
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* Bitcoin Improvement Proposal 340 "Schnorr Signatures for secp256k1"
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* (https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki).
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*/
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/** A pointer to a function to deterministically generate a nonce.
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*
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* Same as secp256k1_nonce function with the exception of accepting an
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* additional pubkey argument and not requiring an attempt argument. The pubkey
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* argument can protect signature schemes with key-prefixed challenge hash
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* inputs against reusing the nonce when signing with the wrong precomputed
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* pubkey.
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*
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* Returns: 1 if a nonce was successfully generated. 0 will cause signing to
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* return an error.
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* Out: nonce32: pointer to a 32-byte array to be filled by the function
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* In: msg: the message being verified. Is NULL if and only if msglen
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* is 0.
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* msglen: the length of the message
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* key32: pointer to a 32-byte secret key (will not be NULL)
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* xonly_pk32: the 32-byte serialized xonly pubkey corresponding to key32
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* (will not be NULL)
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* algo: pointer to an array describing the signature
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* algorithm (will not be NULL)
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* algolen: the length of the algo array
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* data: arbitrary data pointer that is passed through
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*
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* Except for test cases, this function should compute some cryptographic hash of
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* the message, the key, the pubkey, the algorithm description, and data.
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*/
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typedef int (*secp256k1_nonce_function_hardened)(
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unsigned char *nonce32,
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const unsigned char *msg,
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size_t msglen,
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const unsigned char *key32,
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const unsigned char *xonly_pk32,
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const unsigned char *algo,
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size_t algolen,
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void *data
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);
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/** An implementation of the nonce generation function as defined in Bitcoin
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* Improvement Proposal 340 "Schnorr Signatures for secp256k1"
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* (https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki).
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*
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* If a data pointer is passed, it is assumed to be a pointer to 32 bytes of
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* auxiliary random data as defined in BIP-340. If the data pointer is NULL,
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* the nonce derivation procedure follows BIP-340 by setting the auxiliary
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* random data to zero. The algo argument must be non-NULL, otherwise the
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* function will fail and return 0. The hash will be tagged with algo.
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* Therefore, to create BIP-340 compliant signatures, algo must be set to
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* "BIP0340/nonce" and algolen to 13.
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*/
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SECP256K1_API extern const secp256k1_nonce_function_hardened secp256k1_nonce_function_bip340;
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/** Data structure that contains additional arguments for schnorrsig_sign_custom.
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*
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* A schnorrsig_extraparams structure object can be initialized correctly by
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* setting it to SECP256K1_SCHNORRSIG_EXTRAPARAMS_INIT.
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*
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* Members:
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* magic: set to SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC at initialization
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* and has no other function than making sure the object is
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* initialized.
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* noncefp: pointer to a nonce generation function. If NULL,
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* secp256k1_nonce_function_bip340 is used
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* ndata: pointer to arbitrary data used by the nonce generation function
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* (can be NULL). If it is non-NULL and
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* secp256k1_nonce_function_bip340 is used, then ndata must be a
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* pointer to 32-byte auxiliary randomness as per BIP-340.
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*/
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typedef struct {
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unsigned char magic[4];
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secp256k1_nonce_function_hardened noncefp;
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void* ndata;
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} secp256k1_schnorrsig_extraparams;
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#define SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC { 0xda, 0x6f, 0xb3, 0x8c }
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#define SECP256K1_SCHNORRSIG_EXTRAPARAMS_INIT {\
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SECP256K1_SCHNORRSIG_EXTRAPARAMS_MAGIC,\
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NULL,\
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NULL\
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}
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/** Create a Schnorr signature.
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*
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* Does _not_ strictly follow BIP-340 because it does not verify the resulting
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* signature. Instead, you can manually use secp256k1_schnorrsig_verify and
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* abort if it fails.
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*
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* This function only signs 32-byte messages. If you have messages of a
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* different size (or the same size but without a context-specific tag
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* prefix), it is recommended to create a 32-byte message hash with
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* secp256k1_tagged_sha256 and then sign the hash. Tagged hashing allows
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* providing an context-specific tag for domain separation. This prevents
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* signatures from being valid in multiple contexts by accident.
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*
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* Returns 1 on success, 0 on failure.
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* Args: ctx: pointer to a context object, initialized for signing.
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* Out: sig64: pointer to a 64-byte array to store the serialized signature.
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* In: msg32: the 32-byte message being signed.
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* keypair: pointer to an initialized keypair.
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* aux_rand32: 32 bytes of fresh randomness. While recommended to provide
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* this, it is only supplemental to security and can be NULL. A
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* NULL argument is treated the same as an all-zero one. See
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* BIP-340 "Default Signing" for a full explanation of this
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* argument and for guidance if randomness is expensive.
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*/
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SECP256K1_API int secp256k1_schnorrsig_sign32(
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const secp256k1_context* ctx,
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unsigned char *sig64,
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const unsigned char *msg32,
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const secp256k1_keypair *keypair,
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const unsigned char *aux_rand32
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
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/** Same as secp256k1_schnorrsig_sign32, but DEPRECATED. Will be removed in
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* future versions. */
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SECP256K1_API int secp256k1_schnorrsig_sign(
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const secp256k1_context* ctx,
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unsigned char *sig64,
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const unsigned char *msg32,
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const secp256k1_keypair *keypair,
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const unsigned char *aux_rand32
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4)
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SECP256K1_DEPRECATED("Use secp256k1_schnorrsig_sign32 instead");
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/** Create a Schnorr signature with a more flexible API.
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*
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* Same arguments as secp256k1_schnorrsig_sign except that it allows signing
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* variable length messages and accepts a pointer to an extraparams object that
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* allows customizing signing by passing additional arguments.
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*
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* Creates the same signatures as schnorrsig_sign if msglen is 32 and the
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* extraparams.ndata is the same as aux_rand32.
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*
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* In: msg: the message being signed. Can only be NULL if msglen is 0.
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* msglen: length of the message
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* extraparams: pointer to a extraparams object (can be NULL)
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*/
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SECP256K1_API int secp256k1_schnorrsig_sign_custom(
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const secp256k1_context* ctx,
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unsigned char *sig64,
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const unsigned char *msg,
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size_t msglen,
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const secp256k1_keypair *keypair,
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secp256k1_schnorrsig_extraparams *extraparams
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(5);
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/** Verify a Schnorr signature.
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*
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* Returns: 1: correct signature
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* 0: incorrect signature
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* Args: ctx: a secp256k1 context object.
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* In: sig64: pointer to the 64-byte signature to verify.
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* msg: the message being verified. Can only be NULL if msglen is 0.
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* msglen: length of the message
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* pubkey: pointer to an x-only public key to verify with (cannot be NULL)
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*/
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SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_schnorrsig_verify(
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const secp256k1_context* ctx,
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const unsigned char *sig64,
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const unsigned char *msg,
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size_t msglen,
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const secp256k1_xonly_pubkey *pubkey
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(5);
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#ifdef __cplusplus
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}
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#endif
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#endif /* SECP256K1_SCHNORRSIG_H */
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