1=pod 2 3=head1 NAME 4 5EVP_PKEY_decapsulate_init, EVP_PKEY_auth_decapsulate_init, EVP_PKEY_decapsulate 6- Key decapsulation using a KEM algorithm with a private key 7 8=head1 SYNOPSIS 9 10 #include <openssl/evp.h> 11 12 int EVP_PKEY_decapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]); 13 int EVP_PKEY_auth_decapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpub, 14 const OSSL_PARAM params[]); 15 int EVP_PKEY_decapsulate(EVP_PKEY_CTX *ctx, 16 unsigned char *unwrapped, size_t *unwrappedlen, 17 const unsigned char *wrapped, size_t wrappedlen); 18 19=head1 DESCRIPTION 20 21The EVP_PKEY_decapsulate_init() function initializes a private key algorithm 22context I<ctx> for a decapsulation operation and then sets the I<params> 23on the context in the same way as calling L<EVP_PKEY_CTX_set_params(3)>. 24Note that I<ctx> usually is produced using L<EVP_PKEY_CTX_new_from_pkey(3)>, 25specifying the private key to use. 26 27The EVP_PKEY_auth_decapsulate_init() function is similar to 28EVP_PKEY_decapsulate_init() but also passes an I<authpub> authentication public 29key that is used during decapsulation. 30 31The EVP_PKEY_decapsulate() function performs a private key decapsulation 32operation using I<ctx>. The data to be decapsulated is specified using the 33I<wrapped> and I<wrappedlen> parameters. 34If I<unwrapped> is NULL then the maximum size of the output secret buffer 35is written to I<*unwrappedlen>. If I<unwrapped> is not NULL and the 36call is successful then the decapsulated secret data is written to I<unwrapped> 37and the amount of data written to I<*unwrappedlen>. 38 39=head1 NOTES 40 41After the call to EVP_PKEY_decapsulate_init() algorithm-specific parameters 42for the operation may be set or modified using L<EVP_PKEY_CTX_set_params(3)>. 43 44=head1 RETURN VALUES 45 46EVP_PKEY_decapsulate_init(), EVP_PKEY_auth_decapsulate_init() and 47EVP_PKEY_decapsulate() return 1 for success and 0 or a negative value for 48failure. In particular a return value of -2 indicates the operation is not 49supported by the private key algorithm. 50 51=head1 EXAMPLES 52 53Decapsulate data using RSA: 54 55 #include <openssl/evp.h> 56 57 /* 58 * NB: assumes rsa_priv_key is an RSA private key, 59 * and that in, inlen are already set up to contain encapsulated data. 60 */ 61 62 EVP_PKEY_CTX *ctx = NULL; 63 size_t secretlen = 0; 64 unsigned char *secret = NULL;; 65 66 ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_priv_key, NULL); 67 if (ctx = NULL) 68 /* Error */ 69 if (EVP_PKEY_decapsulate_init(ctx, NULL) <= 0) 70 /* Error */ 71 72 /* Set the mode - only 'RSASVE' is currently supported */ 73 if (EVP_PKEY_CTX_set_kem_op(ctx, "RSASVE") <= 0) 74 /* Error */ 75 76 /* Determine buffer length */ 77 if (EVP_PKEY_decapsulate(ctx, NULL, &secretlen, in, inlen) <= 0) 78 /* Error */ 79 80 secret = OPENSSL_malloc(secretlen); 81 if (secret == NULL) 82 /* malloc failure */ 83 84 /* Decapsulated secret data is secretlen bytes long */ 85 if (EVP_PKEY_decapsulate(ctx, secret, &secretlen, in, inlen) <= 0) 86 /* Error */ 87 88 89=head1 SEE ALSO 90 91L<EVP_PKEY_CTX_new_from_pkey(3)>, 92L<EVP_PKEY_encapsulate(3)>, 93L<EVP_KEM-RSA(7)>, L<EVP_KEM-X25519(7)>, L<EVP_KEM-EC(7)> 94 95=head1 HISTORY 96 97The functions EVP_PKEY_decapsulate_init() and EVP_PKEY_decapsulate() were added 98in OpenSSL 3.0. 99 100The function EVP_PKEY_auth_decapsulate_init() was added in OpenSSL 3.2. 101 102=head1 COPYRIGHT 103 104Copyright 2020-2023 The OpenSSL Project Authors. All Rights Reserved. 105 106Licensed under the Apache License 2.0 (the "License"). You may not use 107this file except in compliance with the License. You can obtain a copy 108in the file LICENSE in the source distribution or at 109L<https://www.openssl.org/source/license.html>. 110 111=cut 112
