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 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>. Note that, if I<unwrappedlen> 38is not NULL in this call, the value it points to must be initialised to the length of 39I<unwrapped>, so that the call can validate it is of sufficient size to hold the 40result of the operation. 41 42=head1 NOTES 43 44After the call to EVP_PKEY_decapsulate_init() algorithm-specific parameters 45for the operation may be set or modified using L<EVP_PKEY_CTX_set_params(3)>. 46 47=head1 RETURN VALUES 48 49EVP_PKEY_decapsulate_init(), EVP_PKEY_auth_decapsulate_init() and 50EVP_PKEY_decapsulate() return 1 for success and 0 or a negative value for 51failure. In particular a return value of -2 indicates the operation is not 52supported by the private key algorithm. 53 54=head1 EXAMPLES 55 56Decapsulate data using RSA: 57 58 #include <openssl/evp.h> 59 60 /* 61 * NB: assumes rsa_priv_key is an RSA private key, 62 * and that in, inlen are already set up to contain encapsulated data. 63 */ 64 65 EVP_PKEY_CTX *ctx = NULL; 66 size_t secretlen = 0; 67 unsigned char *secret = NULL;; 68 69 ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_priv_key, NULL); 70 if (ctx == NULL) 71 /* Error */ 72 if (EVP_PKEY_decapsulate_init(ctx, NULL) <= 0) 73 /* Error */ 74 75 /* Set the mode - only 'RSASVE' is currently supported */ 76 if (EVP_PKEY_CTX_set_kem_op(ctx, "RSASVE") <= 0) 77 /* Error */ 78 79 /* Determine buffer length */ 80 if (EVP_PKEY_decapsulate(ctx, NULL, &secretlen, in, inlen) <= 0) 81 /* Error */ 82 83 secret = OPENSSL_malloc(secretlen); 84 if (secret == NULL) 85 /* malloc failure */ 86 87 /* Decapsulated secret data is secretlen bytes long */ 88 if (EVP_PKEY_decapsulate(ctx, secret, &secretlen, in, inlen) <= 0) 89 /* Error */ 90 91 92=head1 SEE ALSO 93 94L<EVP_PKEY_CTX_new_from_pkey(3)>, 95L<EVP_PKEY_encapsulate(3)>, 96L<EVP_KEM-RSA(7)>, L<EVP_KEM-X25519(7)>, L<EVP_KEM-EC(7)> 97 98=head1 HISTORY 99 100The functions EVP_PKEY_decapsulate_init() and EVP_PKEY_decapsulate() were added 101in OpenSSL 3.0. 102 103The function EVP_PKEY_auth_decapsulate_init() was added in OpenSSL 3.2. 104 105=head1 COPYRIGHT 106 107Copyright 2020-2023 The OpenSSL Project Authors. All Rights Reserved. 108 109Licensed under the Apache License 2.0 (the "License"). You may not use 110this file except in compliance with the License. You can obtain a copy 111in the file LICENSE in the source distribution or at 112L<https://www.openssl.org/source/license.html>. 113 114=cut 115
