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
TheEVP_PKEY_derive_init()
function initializes a public key algorithm context using key
ctx->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()
function 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.
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.
EXAMPLES
Derive shared secret (for example DH or EC keys):
#include <openssl/evp.h> #include <openssl/rsa.h> EVP_PKEY_CTX *ctx; ENGINE *eng; unsigned char *skey; size_t skeylen; EVP_PKEY *pkey, *peerkey; /* Assumes that pkey, eng, and peerkey have already been set up. */ ctx = EVP_PKEY_CTX_new(pkey, eng); 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 = 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_decrypt(3), EVP_PKEY_encrypt(3), EVP_PKEY_meth_set_derive(3), EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3), X25519(3)
HISTORY
EVP_PKEY_derive_init(),
EVP_PKEY_derive_set_peer(), and
EVP_PKEY_derive() first appeared in OpenSSL 1.0.0
and have been available since OpenBSD 4.9.