EVP_PKEY_derive (3)
Leading comments
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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 exampleDH
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 */