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