xref: /openssl/doc/man3/EVP_PKEY_decapsulate.pod (revision 3c2bdd7d) 
1=pod
2
3=head1 NAME
4
5EVP_PKEY_decapsulate_init, EVP_PKEY_decapsulate
6- Key decapsulation using a private key algorithm
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 *secret, size_t *secretlen,
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)>.
22
23The EVP_PKEY_decapsulate() function performs a private key decapsulation
24operation using I<ctx>. The data to be decapsulated is specified using the
25I<wrapped> and I<wrappedlen> parameters.
26If I<secret> is I<NULL> then the maximum size of the output secret buffer
27is written to the I<*secretlen> parameter. If I<secret> is not B<NULL> and the
28call is successful then the decapsulated secret data is written to I<secret> and
29the amount of data written to I<secretlen>.
30
31=head1 NOTES
32
33After the call to EVP_PKEY_decapsulate_init() algorithm specific parameters
34for the operation may be set or modified using L<EVP_PKEY_CTX_set_params(3)>.
35
36=head1 RETURN VALUES
37
38EVP_PKEY_decapsulate_init() and EVP_PKEY_decapsulate() return 1 for
39success and 0 or a negative value for failure. In particular a return value of -2
40indicates the operation is not supported by the private key algorithm.
41
42=head1 EXAMPLES
43
44Decapsulate data using RSA:
45
46 #include <openssl/evp.h>
47
48 /*
49  * NB: assumes rsa_priv_key is an RSA private key,
50  * and that in, inlen are already set up to contain encapsulated data.
51  */
52
53 EVP_PKEY_CTX *ctx = NULL;
54 size_t secretlen = 0;
55 unsigned char *secret = NULL;;
56
57 ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_priv_key, NULL);
58 if (ctx = NULL)
59     /* Error */
60 if (EVP_PKEY_decapsulate_init(ctx, NULL) <= 0)
61     /* Error */
62
63 /* Set the mode - only 'RSASVE' is currently supported */
64 if (EVP_PKEY_CTX_set_kem_op(ctx, "RSASVE") <= 0)
65     /* Error */
66
67 /* Determine buffer length */
68 if (EVP_PKEY_decapsulate(ctx, NULL, &secretlen, in, inlen) <= 0)
69     /* Error */
70
71 secret = OPENSSL_malloc(secretlen);
72 if (secret == NULL)
73     /* malloc failure */
74
75 /* Decapsulated secret data is secretlen bytes long */
76 if (EVP_PKEY_decapsulaterctx, secret, &secretlen, in, inlen) <= 0)
77     /* Error */
78
79
80=head1 SEE ALSO
81
82L<EVP_PKEY_CTX_new(3)>,
83L<EVP_PKEY_encapsulate(3)>,
84L<EVP_KEM-RSA(7)>,
85
86=head1 HISTORY
87
88These functions were added in OpenSSL 3.0.
89
90=head1 COPYRIGHT
91
92Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.
93
94Licensed under the Apache License 2.0 (the "License").  You may not use
95this file except in compliance with the License.  You can obtain a copy
96in the file LICENSE in the source distribution or at
97L<https://www.openssl.org/source/license.html>.
98
99=cut
100