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secp256k1_ecdh.h File Reference
#include "secp256k1.h"
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Typedefs

typedef int(* secp256k1_ecdh_hash_function) (unsigned char *output, const unsigned char *x32, const unsigned char *y32, void *data)
 

Functions

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)
 

Variables

SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_sha256
 
SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default
 

Typedef Documentation

◆ secp256k1_ecdh_hash_function

typedef int(* secp256k1_ecdh_hash_function) (unsigned char *output, const unsigned char *x32, const unsigned char *y32, void *data)

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

Definition at line 21 of file secp256k1_ecdh.h.

Function Documentation

◆ secp256k1_ecdh()

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 
)

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.

29  {
30  int ret = 0;
31  int overflow = 0;
33  secp256k1_ge pt;
35  unsigned char x[32];
36  unsigned char y[32];
37 
38  VERIFY_CHECK(ctx != NULL);
39  ARG_CHECK(output != NULL);
40  ARG_CHECK(point != NULL);
41  ARG_CHECK(scalar != NULL);
42 
43  if (hashfp == NULL) {
45  }
46 
47  secp256k1_pubkey_load(ctx, &pt, point);
48  secp256k1_scalar_set_b32(&s, scalar, &overflow);
49 
50  overflow |= secp256k1_scalar_is_zero(&s);
51  secp256k1_scalar_cmov(&s, &secp256k1_scalar_one, overflow);
52 
53  secp256k1_ecmult_const(&res, &pt, &s, 256);
54  secp256k1_ge_set_gej(&pt, &res);
55 
56  /* Compute a hash of the point */
57  secp256k1_fe_normalize(&pt.x);
58  secp256k1_fe_normalize(&pt.y);
59  secp256k1_fe_get_b32(x, &pt.x);
60  secp256k1_fe_get_b32(y, &pt.y);
61 
62  ret = hashfp(output, x, y, data);
63 
64  memset(x, 0, 32);
65  memset(y, 0, 32);
66  secp256k1_scalar_clear(&s);
67 
68  return !!ret & !overflow;
69 }
const char * res
Definition: hmac_keccak.cpp:41
#define VERIFY_CHECK(cond)
Definition: util.h:96
secp256k1_fe x
Definition: group.h:17
const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default
Definition: main_impl.h:27
secp256k1_fe y
Definition: group.h:18

Variable Documentation

◆ secp256k1_ecdh_hash_function_default

SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_function_default

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

SECP256K1_API const secp256k1_ecdh_hash_function secp256k1_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.