/usr/man/cat.3/EVP_PKEY_derive.3

EVP_PKEY_derive(3)           OpenSSL           EVP_PKEY_derive(3)

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>

1.0.2t               Last change: 2019-09-10                    1

EVP_PKEY_derive(3)           OpenSSL           EVP_PKEY_derive(3)

      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.

1.0.2t               Last change: 2019-09-10                    2

See also EVP_PKEY_derive_init(3)
See also EVP_PKEY_derive_set_peer(3)