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#ifndef SECP256K1_ECDH_H
#define SECP256K1_ECDH_H
#include "secp256k1.h"
#ifdef __cplusplus
extern "C" {
#endif
/** A pointer to a function that hashes an EC point to obtain an ECDH secret
*
* Returns: 1 if the point was successfully hashed.
* 0 will cause secp256k1_ecdh to fail and return 0.
* Other return values are not allowed, and the behaviour of
* secp256k1_ecdh is undefined for other return values.
* Out: output: pointer to an array to be filled by the function
* In: x32: pointer to a 32-byte x coordinate
* y32: pointer to a 32-byte y coordinate
* data: arbitrary data pointer that is passed through
*/
typedef int (*secp256k1_ecdh_hash_function)(
unsigned char *output,
const unsigned char *x32,
const unsigned char *y32,
void *data
);
/** An implementation of SHA256 hash function that applies to compressed public key.
* Populates the output parameter with 32 bytes. */
SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256;
/** A default ECDH hash function (currently equal to secp256k1_ecdh_hash_function_sha256).
* Populates the output parameter with 32 bytes. */
SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default;
/** Compute an EC Diffie-Hellman secret in constant time
*
* Returns: 1: exponentiation was successful
* 0: scalar was invalid (zero or overflow) or hashfp returned 0
* Args: ctx: pointer to a context object (cannot be NULL)
* Out: output: pointer to an array to be filled by hashfp
* In: pubkey: a pointer to a secp256k1_pubkey containing an
* initialized public key
* seckey: a 32-byte scalar with which to multiply the point
* hashfp: pointer to a hash function. If NULL, secp256k1_ecdh_hash_function_sha256 is used
* (in which case, 32 bytes will be written to output)
* data: arbitrary data pointer that is passed through to hashfp
*/
SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdh(
const secp256k1_context* ctx,
unsigned char *output,
const secp256k1_pubkey *pubkey,
const unsigned char *seckey,
secp256k1_ecdh_hash_function hashfp,
void *data
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);
#ifdef __cplusplus
}
#endif
#endif /* SECP256K1_ECDH_H */
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