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