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EVP_PKEY_DERIVE(3) Library Functions Manual EVP_PKEY_DERIVE(3)

EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derivederive public key algorithm shared secret

#include <openssl/evp.h>

EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);

EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);

EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);

The () function initializes a public key algorithm context using key ctx->pkey for shared secret derivation.

The () function sets the peer key: this will normally be a public key.

The () 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 (), algorithm specific control operations can be performed to set any appropriate parameters for the operation.

The function () can be called more than once on the same context if several operations are performed using the same parameters.

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.

Derive shared secret (for example DH or EC keys):

#include <openssl/evp.h>
#include <openssl/rsa.h>

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 */

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)

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.

March 23, 2018 OpenBSD-6.9