libsec.h

#define SECP256K1_CONTEXT_VERIFY ...
#define SECP256K1_CONTEXT_SIGN ...
#define SECP256K1_EC_COMPRESSED ...
#define SECP256K1_EC_UNCOMPRESSED ...

typedef struct secp256k1_context_struct secp256k1_context;

secp256k1_context* secp256k1_context_create(unsigned int flags);
void secp256k1_context_destroy(secp256k1_context* ctx);

typedef struct {
    unsigned char data[64];
} secp256k1_pubkey;

int secp256k1_ec_pubkey_parse(const secp256k1_context* ctx, secp256k1_pubkey* pubkey, const unsigned char *input, size_t inputlen);
int secp256k1_ec_pubkey_serialize(const secp256k1_context* ctx, unsigned char *output, size_t *outputlen, const secp256k1_pubkey* pubkey, unsigned int flags);
int secp256k1_ec_pubkey_tweak_add(const secp256k1_context* ctx, secp256k1_pubkey *pubkey, const unsigned char *tweak);
int secp256k1_ec_pubkey_tweak_mul(const secp256k1_context* ctx, secp256k1_pubkey *pubkey, const unsigned char *tweak);

typedef struct {
    unsigned char data[64];
} secp256k1_ecdsa_signature;

int secp256k1_ecdsa_signature_parse_der(const secp256k1_context* ctx, secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen);
int secp256k1_ecdsa_signature_serialize_der(const secp256k1_context* ctx, unsigned char *output, size_t *outputlen, const secp256k1_ecdsa_signature* sig);
int secp256k1_ecdsa_verify(const secp256k1_context* ctx, const secp256k1_ecdsa_signature *sig, const unsigned char *msg32, const secp256k1_pubkey *pubkey);

typedef int (*secp256k1_nonce_function)(
    unsigned char *nonce32,
    const unsigned char *msg32,
    const unsigned char *key32,
    const unsigned char *algo16,
    void *data,
    unsigned int attempt
);

int secp256k1_ecdsa_sign(const secp256k1_context* ctx, secp256k1_ecdsa_signature *sig, const unsigned char *msg32, const unsigned char *seckey, secp256k1_nonce_function noncefp, const void *ndata);