| =pod |
| |
| =head1 NAME |
| |
| EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key algorithm shared secret. |
| |
| =head1 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); |
| |
| =head1 DESCRIPTION |
| |
| The EVP_PKEY_derive_init() function initializes a public key algorithm |
| context using key B<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 B<ctx>. |
| If B<key> is B<NULL> then the maximum size of the output buffer is written to |
| the B<keylen> parameter. If B<key> is not B<NULL> then before the call the |
| B<keylen> parameter should contain the length of the B<key> buffer, if the call |
| is successful the shared secret is written to B<key> and the amount of data |
| written to B<keylen>. |
| |
| =head1 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. |
| |
| =head1 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. |
| |
| =head1 EXAMPLE |
| |
| Derive shared secret (for example DH 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 */ |
| |
| =head1 SEE ALSO |
| |
| L<EVP_PKEY_CTX_new(3)>, |
| L<EVP_PKEY_encrypt(3)>, |
| L<EVP_PKEY_decrypt(3)>, |
| L<EVP_PKEY_sign(3)>, |
| L<EVP_PKEY_verify(3)>, |
| L<EVP_PKEY_verify_recover(3)>, |
| |
| =head1 HISTORY |
| |
| These functions were first added to OpenSSL 1.0.0. |
| |
| =cut |
