| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | DH_generate_key, DH_compute_key, DH_compute_key_padded - perform
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| 6 | Diffie-Hellman key exchange
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| 7 |
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| 8 | =head1 SYNOPSIS
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| 9 |
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| 10 | #include <openssl/dh.h>
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| 11 |
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| 12 | int DH_generate_key(DH *dh);
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| 13 |
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| 14 | int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
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| 15 |
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| 16 | int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh);
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| 17 |
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| 18 | =head1 DESCRIPTION
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| 19 |
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| 20 | DH_generate_key() performs the first step of a Diffie-Hellman key
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| 21 | exchange by generating private and public DH values. By calling
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| 22 | DH_compute_key() or DH_compute_key_padded(), these are combined with
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| 23 | the other party's public value to compute the shared key.
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| 24 |
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| 25 | DH_generate_key() expects B<dh> to contain the shared parameters
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| 26 | B<dh-E<gt>p> and B<dh-E<gt>g>. It generates a random private DH value
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| 27 | unless B<dh-E<gt>priv_key> is already set, and computes the
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| 28 | corresponding public value B<dh-E<gt>pub_key>, which can then be
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| 29 | published.
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| 30 |
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| 31 | DH_compute_key() computes the shared secret from the private DH value
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| 32 | in B<dh> and the other party's public value in B<pub_key> and stores
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| 33 | it in B<key>. B<key> must point to B<DH_size(dh)> bytes of memory.
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| 34 | The padding style is RFC 5246 (8.1.2) that strips leading zero bytes.
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| 35 | It is not constant time due to the leading zero bytes being stripped.
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| 36 | The return value should be considered public.
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| 37 |
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| 38 | DH_compute_key_padded() is similar but stores a fixed number of bytes.
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| 39 | The padding style is NIST SP 800-56A (C.1) that retains leading zero bytes.
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| 40 | It is constant time due to the leading zero bytes being retained.
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| 41 | The return value should be considered public.
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| 42 |
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| 43 | =head1 RETURN VALUES
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| 44 |
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| 45 | DH_generate_key() returns 1 on success, 0 otherwise.
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| 46 |
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| 47 | DH_compute_key() returns the size of the shared secret on success, -1
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| 48 | on error.
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| 49 |
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| 50 | DH_compute_key_padded() returns B<DH_size(dh)> on success, -1 on error.
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| 51 |
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| 52 | The error codes can be obtained by L<ERR_get_error(3)>.
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| 53 |
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| 54 | =head1 SEE ALSO
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| 55 |
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| 56 | L<DH_new(3)>, L<ERR_get_error(3)>, L<RAND_bytes(3)>, L<DH_size(3)>
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| 57 |
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| 58 | =head1 HISTORY
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| 59 |
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| 60 | DH_compute_key_padded() was added in OpenSSL 1.0.2.
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| 61 |
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| 62 | =head1 COPYRIGHT
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| 63 |
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| 64 | Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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| 65 |
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| 66 | Licensed under the OpenSSL license (the "License"). You may not use
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| 67 | this file except in compliance with the License. You can obtain a copy
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| 68 | in the file LICENSE in the source distribution or at
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| 69 | L<https://www.openssl.org/source/license.html>.
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| 70 |
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| 71 | =cut
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