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0c679f5566
Reviewed-by: Neil Horman <nhorman@openssl.org> Reviewed-by: Matt Caswell <matt@openssl.org> Release: yes
145 lines
5.1 KiB
Plaintext
145 lines
5.1 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY_encapsulate_init, EVP_PKEY_auth_encapsulate_init, EVP_PKEY_encapsulate
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- Key encapsulation using a KEM algorithm with a public key
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_PKEY_encapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
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int EVP_PKEY_auth_encapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpriv,
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const OSSL_PARAM params[]);
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int EVP_PKEY_encapsulate(EVP_PKEY_CTX *ctx,
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unsigned char *wrappedkey, size_t *wrappedkeylen,
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unsigned char *genkey, size_t *genkeylen);
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=head1 DESCRIPTION
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The EVP_PKEY_encapsulate_init() function initializes a public key algorithm
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context I<ctx> for an encapsulation operation and then sets the I<params>
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on the context in the same way as calling L<EVP_PKEY_CTX_set_params(3)>.
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Note that I<ctx> is usually is produced using L<EVP_PKEY_CTX_new_from_pkey(3)>,
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specifying the public key to use.
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The EVP_PKEY_auth_encapsulate_init() function is similar to
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EVP_PKEY_encapsulate_init() but also passes an I<authpriv> authentication private
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key that is used during encapsulation.
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The EVP_PKEY_encapsulate() function performs a public key encapsulation
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operation using I<ctx>.
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The shared secret writen to I<genkey> can be used as an input for key
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derivation, typically for various symmetric algorithms.
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Its size is written to I<genkeylen>, which must be initialised to the
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size of the provided buffer.
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The ciphertext written to I<wrappedkey> is an encapsulated form, which
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is expected to be only usable by the holder of the private key corresponding
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to wthe public key associated with I<ctx>.
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This ciphertext is then communicated to the private-key holder, who can use
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L<EVP_PKEY_decapsulate(3)> to securely recover the same shared secret.
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If I<wrappedkey> is NULL then the maximum size of the output buffer is written
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to the I<*wrappedkeylen> parameter unless I<wrappedkeylen> is NULL and the
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maximum size of the generated key buffer is written to I<*genkeylen> unless
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I<genkeylen> is NULL.
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If I<wrappedkey> is not NULL and the call is successful then the generated
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shared secret is written to I<genkey> and its size is written to
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I<*genkeylen> (which must be non-NULL).
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The encapsulated ciphertext is written to I<wrappedkey> and
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its size is written to I<*wrappedkeylen> (must also be non-NULL),
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The value pointed to by I<wrappedlen> initially hold the size of the
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I<unwrapped> buffer so that its size can be validated by the call, ensuring it
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is large enough to hold the result written to I<wrapped>.
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Absent detailed prior knowledge of the internals of the specific KEM
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algorithm, callers SHOULD NOT assume that the returned shared secret and
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ciphertext are necessarily of the maximum possible length.
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The lengths returned via I<*wrappedkeylen> and I<*genkeylen> SHOULD
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be used to determine the actual lengths of the outputs.
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=head1 NOTES
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After the call to EVP_PKEY_encapsulate_init(), algorithm-specific parameters
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for the operation may be set or modified using L<EVP_PKEY_CTX_set_params(3)>.
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=head1 RETURN VALUES
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EVP_PKEY_encapsulate_init(), EVP_PKEY_auth_encapsulate_init() and
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EVP_PKEY_encapsulate() return 1 for success and 0 or a negative value for
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failure. In particular a return value of -2 indicates the operation is not
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supported by the public key algorithm.
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=head1 EXAMPLES
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Encapsulate an RSASVE key (for RSA keys).
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#include <openssl/evp.h>
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/*
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* NB: assumes rsa_pub_key is an public key of another party.
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*/
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EVP_PKEY_CTX *ctx = NULL;
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size_t secretlen = 0, outlen = 0;
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unsigned char *out = NULL, *secret = NULL;
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ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_pub_key, NULL);
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if (ctx == NULL)
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/* Error */
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if (EVP_PKEY_encapsulate_init(ctx, NULL) <= 0)
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/* Error */
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/* Set the mode - only 'RSASVE' is currently supported */
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if (EVP_PKEY_CTX_set_kem_op(ctx, "RSASVE") <= 0)
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/* Error */
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/* Determine buffer length */
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if (EVP_PKEY_encapsulate(ctx, NULL, &outlen, NULL, &secretlen) <= 0)
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/* Error */
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out = OPENSSL_malloc(outlen);
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secret = OPENSSL_malloc(secretlen);
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if (out == NULL || secret == NULL)
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/* malloc failure */
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/*
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* The generated 'secret' can be used as key material.
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* The encapsulated 'out' can be sent to another party who can
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* decapsulate it using their private key to retrieve the 'secret'.
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*/
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if (EVP_PKEY_encapsulate(ctx, out, &outlen, secret, &secretlen) <= 0)
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/* Error */
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=head1 SEE ALSO
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L<EVP_PKEY_CTX_new_from_pkey(3)>,
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L<EVP_PKEY_decapsulate(3)>,
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L<EVP_KEM-RSA(7)>,
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L<EVP_KEM-X25519(7)>,
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L<EVP_KEM-EC(7)>,
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L<EVP_KEM-ML-KEM-512(7)>,
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L<EVP_KEM-ML-KEM-768(7)>,
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L<EVP_KEM-ML-KEM-1024(7)>
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=head1 HISTORY
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The functions EVP_PKEY_encapsulate_init() and EVP_PKEY_encapsulate() were
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added in OpenSSL 3.0.
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The function EVP_PKEY_auth_encapsulate_init() was added in OpenSSL 3.2.
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Support for B<ML-KEM> was added in OpenSSL 3.5.
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=head1 COPYRIGHT
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Copyright 2020-2025 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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