EVP_PKEY_derive

NAME

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_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

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

EXAMPLE

 #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

HISTORY