bitcoin/include/secp256k1.h

#ifndef _SECP256K1_
#define _SECP256K1_

#ifdef __cplusplus
extern "C" {
#endif

/** Flags to pass to secp256k1_start. */
#define SECP256K1_START_VERIFY (1 << 0)
#define SECP256K1_START_SIGN   (1 << 1)

/** Initialize the library. This may take some time (10-100 ms).
 *  You need to call this before calling any other function.
 *  It cannot run in parallel with any other functions, but once
 *  secp256k1_start() returns, all other functions are thread-safe.
 */
void secp256k1_start(unsigned int flags);

/** Free all memory associated with this library. After this, no
 *  functions can be called anymore, except secp256k1_start()
 */
void secp256k1_stop(void);

/** Verify an ECDSA signature.
 *  Returns: 1: correct signature
 *           0: incorrect signature
 *          -1: invalid public key
 *          -2: invalid signature
 * In:       msg:       the message being verified (cannot be NULL)
 *           msglen:    the length of the message (at most 32)
 *           sig:       the signature being verified (cannot be NULL)
 *           siglen:    the length of the signature
 *           pubkey:    the public key to verify with (cannot be NULL)
 *           pubkeylen: the length of pubkey
 * Requires starting using SECP256K1_START_VERIFY.
 */
int secp256k1_ecdsa_verify(const unsigned char *msg, int msglen,
                           const unsigned char *sig, int siglen,
                           const unsigned char *pubkey, int pubkeylen);

/** Create an ECDSA signature.
 *  Returns: 1: signature created
 *           0: nonce invalid, try another one
 *  In:      msg:    the message being signed (cannot be NULL)
 *           msglen: the length of the message being signed (at most 32)
 *           seckey: pointer to a 32-byte secret key (cannot be NULL, assumed to be valid)
 *           nonce:  pointer to a 32-byte nonce (cannot be NULL, generated with a cryptographic PRNG)
 *  Out:     sig:    pointer to an array where the signature will be placed (cannot be NULL)
 *  In/Out:  siglen: pointer to an int with the length of sig, which will be updated
 *                   to contain the actual signature length (<=72).
 * Requires starting using SECP256K1_START_SIGN.
 */
int secp256k1_ecdsa_sign(const unsigned char *msg, int msglen,
                         unsigned char *sig, int *siglen,
                         const unsigned char *seckey,
                         const unsigned char *nonce);

/** Create a compact ECDSA signature (64 byte + recovery id).
 *  Returns: 1: signature created
 *           0: nonce invalid, try another one
 *  In:      msg:    the message being signed (cannot be NULL)
 *           msglen: the length of the message being signed (at most 32)
 *           seckey: pointer to a 32-byte secret key (cannot be NULL, assumed to be valid)
 *           nonce:  pointer to a 32-byte nonce (cannot be NULL, generated with a cryptographic PRNG)
 *  Out:     sig:    pointer to a 64-byte array where the signature will be placed (cannot be NULL)
 *           recid:  pointer to an int, which will be updated to contain the recovery id (can be NULL)
 * Requires starting using SECP256K1_START_SIGN.
 */
int secp256k1_ecdsa_sign_compact(const unsigned char *msg, int msglen,
                                 unsigned char *sig64,
                                 const unsigned char *seckey,
                                 const unsigned char *nonce,
                                 int *recid);

/** Recover an ECDSA public key from a compact signature.
 *  Returns: 1: public key successfully recovered (which guarantees a correct signature).
 *           0: otherwise.
 *  In:      msg:        the message assumed to be signed (cannot be NULL)
 *           msglen:     the length of the message (at most 32)
 *           sig64:      signature as 64 byte array (cannot be NULL)
 *           compressed: whether to recover a compressed or uncompressed pubkey
 *           recid:      the recovery id (0-3, as returned by ecdsa_sign_compact)
 *  Out:     pubkey:     pointer to a 33 or 65 byte array to put the pubkey (cannot be NULL)
 *           pubkeylen:  pointer to an int that will contain the pubkey length (cannot be NULL)
 * Requires starting using SECP256K1_START_VERIFY.
 */
int secp256k1_ecdsa_recover_compact(const unsigned char *msg, int msglen,
                                    const unsigned char *sig64,
                                    unsigned char *pubkey, int *pubkeylen,
                                    int compressed, int recid);

/** Verify an ECDSA secret key.
 *  Returns: 1: secret key is valid
 *           0: secret key is invalid
 *  In:      seckey: pointer to a 32-byte secret key (cannot be NULL)
 */
int secp256k1_ec_seckey_verify(const unsigned char *seckey);

/** Just validate a public key.
 *  Returns: 1: valid public key
 *           0: invalid public key
 *  In:      pubkey:    pointer to a 33-byte or 65-byte public key (cannot be NULL).
 *           pubkeylen: length of pubkey
 */
int secp256k1_ec_pubkey_verify(const unsigned char *pubkey, int pubkeylen);

/** Compute the public key for a secret key.
 *  In:     compressed: whether the computed public key should be compressed
 *          seckey:     pointer to a 32-byte private key (cannot be NULL)
 *  Out:    pubkey:     pointer to a 33-byte (if compressed) or 65-byte (if uncompressed)
 *                      area to store the public key (cannot be NULL)
 *          pubkeylen:  pointer to int that will be updated to contains the pubkey's
 *                      length (cannot be NULL)
 *  Returns: 1: secret was valid, public key stores
 *           0: secret was invalid, try again.
 * Requires starting using SECP256K1_START_SIGN.
 */
int secp256k1_ec_pubkey_create(unsigned char *pubkey, int *pubkeylen, const unsigned char *seckey, int compressed);

/** Decompress a public key.
 * In/Out: pubkey:    pointer to a 65-byte array to put the decompressed public key.
                      It must contain a 33-byte or 65-byte public key already (cannot be NULL)
 *         pubkeylen: pointer to the size of the public key pointed to by pubkey (cannot be NULL)
                      It will be updated to reflect the new size.
 * Returns: 0 if the passed public key was invalid, 1 otherwise. If 1 is returned, the
            pubkey is replaced with its decompressed version.
 */
int secp256k1_ec_pubkey_decompress(unsigned char *pubkey, int *pubkeylen);

/** Export a private key in DER format. */
int secp256k1_ec_privkey_export(const unsigned char *seckey,
                                unsigned char *privkey, int *privkeylen,
                                int compressed);

/** Import a private key in DER format. */
int secp256k1_ec_privkey_import(unsigned char *seckey,
                                const unsigned char *privkey, int privkeylen);

/** Tweak a private key by adding tweak to it. */
int secp256k1_ec_privkey_tweak_add(unsigned char *seckey, const unsigned char *tweak);

/** Tweak a public key by adding tweak times the generator to it.
 * Requires starting with SECP256K1_START_VERIFY.
 */
int secp256k1_ec_pubkey_tweak_add(unsigned char *pubkey, int pubkeylen, const unsigned char *tweak);

/** Tweak a private key by multiplying it with tweak. */
int secp256k1_ec_privkey_tweak_mul(unsigned char *seckey, const unsigned char *tweak);

/** Tweak a public key by multiplying it with tweak.
 * Requires starting with SECP256K1_START_VERIFY.
 */
int secp256k1_ec_pubkey_tweak_mul(unsigned char *pubkey, int pubkeylen, const unsigned char *tweak);

#ifdef __cplusplus
}
#endif

#endif