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ECDH_COMPUTE_KEY(3) Library Functions Manual ECDH_COMPUTE_KEY(3)

ECDH_compute_key, ECDH_sizeElliptic Curve Diffie-Hellman key exchange

#include <openssl/ecdh.h>

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));

ECDH_size(const EC_KEY *ecdh);

() 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).

() 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.

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.

DH_generate_key(3), DH_size(3), EC_GROUP_new(3), EC_KEY_new(3), EC_POINT_new(3), X25519(3)

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.

March 12, 2021 OpenBSD-current