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0c679f5566
Reviewed-by: Neil Horman <nhorman@openssl.org> Reviewed-by: Matt Caswell <matt@openssl.org> Release: yes
137 lines
4.6 KiB
Plaintext
137 lines
4.6 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY_decapsulate_init, EVP_PKEY_auth_decapsulate_init, EVP_PKEY_decapsulate
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- Key decapsulation using a KEM algorithm with a private key
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_PKEY_decapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
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int EVP_PKEY_auth_decapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpub,
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const OSSL_PARAM params[]);
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int EVP_PKEY_decapsulate(EVP_PKEY_CTX *ctx,
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unsigned char *unwrapped, size_t *unwrappedlen,
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const unsigned char *wrapped, size_t wrappedlen);
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=head1 DESCRIPTION
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The EVP_PKEY_decapsulate_init() function initializes a private key algorithm
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context I<ctx> for a decapsulation 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> usually is produced using L<EVP_PKEY_CTX_new_from_pkey(3)>,
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specifying the private key to use.
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The EVP_PKEY_auth_decapsulate_init() function is similar to
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EVP_PKEY_decapsulate_init() but also passes an I<authpub> authentication public
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key that is used during decapsulation.
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The EVP_PKEY_decapsulate() function performs a private key decapsulation
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operation using I<ctx>. The data to be decapsulated is specified using the
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I<wrapped> and I<wrappedlen> parameters (which must both non-NULL).
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The I<wrapped> parameter is an output argument, to which the decapsulated
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shared secret is written.
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The shared secret may not match the peer's value even when decapsulation
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returns success.
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Instead, the shared secret must be used to derive a key that is used to
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authenticate data subsequently received from the peer.
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If I<unwrapped> is NULL then the size of the output shared secret buffer is
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written to I<*unwrappedlen> and no decapsulation is performed, this makes it
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possible to determine the required buffer size at run time. Otherwise, the
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decapsulated secret data is written to I<unwrapped> and the length of shared
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secret is written to I<*unwrappedlen>.
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Note that the value pointed to by I<unwrappedlen> (which must NOT be B<NULL>)
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must be initialised to the length of I<unwrapped>, so that the call can
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validate it is of sufficient size to hold the result of the operation.
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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
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is necessarily of the maximum possible length.
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The length returned via I<*unwrappedlen> SHOULD be used to determine the actual
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length of the output.
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=head1 NOTES
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After the call to EVP_PKEY_decapsulate_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_decapsulate_init(), EVP_PKEY_auth_decapsulate_init() and
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EVP_PKEY_decapsulate() 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 private key algorithm.
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=head1 EXAMPLES
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Decapsulate data using RSA:
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#include <openssl/evp.h>
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/*
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* NB: assumes rsa_priv_key is an RSA private key,
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* and that in, inlen are already set up to contain encapsulated data.
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*/
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EVP_PKEY_CTX *ctx = NULL;
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size_t secretlen = 0;
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unsigned char *secret = NULL;;
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ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_priv_key, NULL);
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if (ctx == NULL)
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/* Error */
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if (EVP_PKEY_decapsulate_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_decapsulate(ctx, NULL, &secretlen, in, inlen) <= 0)
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/* Error */
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secret = OPENSSL_malloc(secretlen);
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if (secret == NULL)
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/* malloc failure */
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/* Decapsulated secret data is secretlen bytes long */
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if (EVP_PKEY_decapsulate(ctx, secret, &secretlen, in, inlen) <= 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_encapsulate(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_decapsulate_init() and EVP_PKEY_decapsulate() were added
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in OpenSSL 3.0.
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The function EVP_PKEY_auth_decapsulate_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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