NAME
ECDH_compute_key,
ECDH_size —
Elliptic Curve Diffie-Hellman key
exchange
SYNOPSIS
#include
<openssl/ecdh.h>
int
ECDH_compute_key(void *out,
size_t outlen, const EC_POINT
*public_key, EC_KEY *ecdh, void
*(*KDF)(const void *in, size_t inlen, void *out, size_t *outlen));
int
ECDH_size(const EC_KEY
*ecdh);
DESCRIPTION
ECDH_compute_key()
performs Elliptic Curve Diffie-Hellman key agreement. It combines the private
key contained in ecdh with the other party's
public_key, takes the x component
of the affine coordinates, and optionally applies the key derivation function
KDF. It stores the resulting symmetric key in the buffer
out, which is outlen bytes long.
If KDF is NULL,
outlen must be at least
ECDH_size(ecdh).
ECDH_size()
returns the number of bytes needed to store an affine coordinate of a point
on the elliptic curve used by ecdh, which is one
eighth of the degree of the finite field underlying that elliptic curve,
rounded up to the next integer number.
RETURN VALUES
ECDH_compute_key() returns the length of
the computed key in bytes or -1 if an error occurs.
ECDH_size() returns the number of bytes
needed to store an affine coordinate.
SEE ALSO
DH_generate_key(3), DH_size(3), EC_GROUP_new(3), EC_KEY_new(3), EC_POINT_new(3), X25519(3)
HISTORY
ECDH_compute_key() first appeared in
OpenSSL 0.9.8 and has been available since OpenBSD
4.5.
ECDH_size() first appeared in
OpenBSD 6.1.