94 lines
2.6 KiB
Plaintext
94 lines
2.6 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key algorithm shared secret.
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
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int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
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int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);
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=head1 DESCRIPTION
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The EVP_PKEY_derive_init() function initializes a public key algorithm
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context using key B<pkey> for shared secret derivation.
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The EVP_PKEY_derive_set_peer() function sets the peer key: this will normally
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be a public key.
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The EVP_PKEY_derive() derives a shared secret using B<ctx>.
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If B<key> is B<NULL> then the maximum size of the output buffer is written to
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the B<keylen> parameter. If B<key> is not B<NULL> then before the call the
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B<keylen> parameter should contain the length of the B<key> buffer, if the call
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is successful the shared secret is written to B<key> and the amount of data
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written to B<keylen>.
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=head1 NOTES
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After the call to EVP_PKEY_derive_init() algorithm specific control
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operations can be performed to set any appropriate parameters for the
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operation.
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The function EVP_PKEY_derive() can be called more than once on the same
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context if several operations are performed using the same parameters.
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=head1 RETURN VALUES
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EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1 for success and 0
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or a negative value for failure. In particular a return value of -2
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indicates the operation is not supported by the public key algorithm.
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=head1 EXAMPLE
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Derive shared secret (for example DH or EC keys):
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#include <openssl/evp.h>
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#include <openssl/rsa.h>
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EVP_PKEY_CTX *ctx;
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unsigned char *skey;
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size_t skeylen;
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EVP_PKEY *pkey, *peerkey;
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/* NB: assumes pkey, peerkey have been already set up */
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ctx = EVP_PKEY_CTX_new(pkey);
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if (!ctx)
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/* Error occurred */
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if (EVP_PKEY_derive_init(ctx) <= 0)
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/* Error */
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if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
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/* Error */
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/* Determine buffer length */
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if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
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/* Error */
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skey = OPENSSL_malloc(skeylen);
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if (!skey)
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/* malloc failure */
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if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
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/* Error */
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/* Shared secret is skey bytes written to buffer skey */
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=head1 SEE ALSO
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L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>,
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L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>,
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L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>,
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L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>,
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L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>,
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L<EVP_PKEY_verify_recover(3)|EVP_PKEY_verify_recover(3)>,
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=head1 HISTORY
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These functions were first added to OpenSSL 1.0.0.
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=cut
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