NAME¶
EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public
key algorithm shared secret.
SYNOPSIS¶
#include <openssl/evp.h>
int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);
DESCRIPTION¶
The
EVP_PKEY_derive_init() function initializes a public key algorithm
context using key
pkey for shared secret derivation.
The
EVP_PKEY_derive_set_peer() function sets the peer key: this will
normally be a public key.
The
EVP_PKEY_derive() derives a shared secret using
ctx. If
key is
NULL then the maximum size of the output buffer is
written to the
keylen parameter. If
key is not
NULL then
before the call the
keylen parameter should contain the length of the
key buffer, if the call is successful the shared secret is written to
key and the amount of data written to
keylen.
NOTES¶
After the call to
EVP_PKEY_derive_init() algorithm specific control
operations can be performed to set any appropriate parameters for the
operation.
The function
EVP_PKEY_derive() can be called more than once on the same
context if several operations are performed using the same parameters.
RETURN VALUES¶
EVP_PKEY_derive_init() and
EVP_PKEY_derive() return 1 for success
and 0 or a negative value for failure. In particular a return value of -2
indicates the operation is not supported by the public key algorithm.
EXAMPLE¶
Derive shared secret (for example DH or EC keys):
#include <openssl/evp.h>
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
unsigned char *skey;
size_t skeylen;
EVP_PKEY *pkey, *peerkey;
/* NB: assumes pkey, peerkey have been already set up */
ctx = EVP_PKEY_CTX_new(pkey);
if (!ctx)
/* Error occurred */
if (EVP_PKEY_derive_init(ctx) <= 0)
/* Error */
if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
/* Error */
/* Determine buffer length */
if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
/* Error */
skey = OPENSSL_malloc(skeylen);
if (!skey)
/* malloc failure */
if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
/* Error */
/* Shared secret is skey bytes written to buffer skey */
SEE ALSO¶
EVP_PKEY_CTX_new(3),
EVP_PKEY_encrypt(3),
EVP_PKEY_decrypt(3),
EVP_PKEY_sign(3),
EVP_PKEY_verify(3),
EVP_PKEY_verify_recover(3),
HISTORY¶
These functions were first added to OpenSSL 1.0.0.