main_impl.h File Reference

#include "../../../include/secp256k1_ecdh.h"
#include "../../ecmult_const_impl.h"

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Functions
int	secp256k1_ecdh (const secp256k1_context *ctx, unsigned char *output, const secp256k1_pubkey *point, const unsigned char *scalar, secp256k1_ecdh_hash_function hashfp, void *data)

Variables
const secp256k1_ecdh_hash_function	secp256k1_ecdh_hash_function_sha256 = ecdh_hash_function_sha256
const secp256k1_ecdh_hash_function	secp256k1_ecdh_hash_function_default = ecdh_hash_function_sha256

Function Documentation

secp256k1_ecdh()

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 )

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. 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 (can be NULL for secp256k1_ecdh_hash_function_sha256).

Definition at line 29 of file main_impl.h.

                                                                                                                                                                                     {
    int ret = 0;
    int overflow = 0;
    secp256k1_gej res;
    secp256k1_ge pt;
    secp256k1_scalar s;
    unsigned char x[32];
    unsigned char y[32];
 
    VERIFY_CHECK(ctx != NULL);
    ARG_CHECK(output != NULL);
    ARG_CHECK(point != NULL);
    ARG_CHECK(scalar != NULL);
 
    if (hashfp == NULL) {
        hashfp = secp256k1_ecdh_hash_function_default;
    }
 
    secp256k1_pubkey_load(ctx, &pt, point);
    secp256k1_scalar_set_b32(&s, scalar, &overflow);
 
    overflow |= secp256k1_scalar_is_zero(&s);
    secp256k1_scalar_cmov(&s, &secp256k1_scalar_one, overflow);
 
    secp256k1_ecmult_const(&res, &pt, &s, 256);
    secp256k1_ge_set_gej(&pt, &res);
 
    /* Compute a hash of the point */
    secp256k1_fe_normalize(&pt.x);
    secp256k1_fe_normalize(&pt.y);
    secp256k1_fe_get_b32(x, &pt.x);
    secp256k1_fe_get_b32(y, &pt.y);
 
    ret = hashfp(output, x, y, data);
 
    memset(x, 0, 32);
    memset(y, 0, 32);
    secp256k1_scalar_clear(&s);
 
    return !!ret & !overflow;
}

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Variable Documentation

secp256k1_ecdh_hash_function_default

const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default = ecdh_hash_function_sha256

A default ECDH hash function (currently equal to secp256k1_ecdh_hash_function_sha256). Populates the output parameter with 32 bytes.

Definition at line 27 of file main_impl.h.

secp256k1_ecdh_hash_function_sha256

const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256 = ecdh_hash_function_sha256

An implementation of SHA256 hash function that applies to compressed public key. Populates the output parameter with 32 bytes.

Definition at line 26 of file main_impl.h.