| 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_set_default_method, DH_get_default_method,
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| 6 | DH_set_method, DH_new_method, DH_OpenSSL - select DH method
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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 | void DH_set_default_method(const DH_METHOD *meth);
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| 13 |
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| 14 | const DH_METHOD *DH_get_default_method(void);
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| 15 |
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| 16 | int DH_set_method(DH *dh, const DH_METHOD *meth);
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| 17 |
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| 18 | DH *DH_new_method(ENGINE *engine);
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| 19 |
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| 20 | const DH_METHOD *DH_OpenSSL(void);
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| 21 |
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| 22 | =head1 DESCRIPTION
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| 23 |
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| 24 | A B<DH_METHOD> specifies the functions that OpenSSL uses for Diffie-Hellman
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| 25 | operations. By modifying the method, alternative implementations
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| 26 | such as hardware accelerators may be used. IMPORTANT: See the NOTES section for
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| 27 | important information about how these DH API functions are affected by the use
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| 28 | of B<ENGINE> API calls.
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| 29 |
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| 30 | Initially, the default DH_METHOD is the OpenSSL internal implementation, as
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| 31 | returned by DH_OpenSSL().
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| 32 |
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| 33 | DH_set_default_method() makes B<meth> the default method for all DH
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| 34 | structures created later.
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| 35 | B<NB>: This is true only whilst no ENGINE has been set
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| 36 | as a default for DH, so this function is no longer recommended.
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| 37 | This function is not thread-safe and should not be called at the same time
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| 38 | as other OpenSSL functions.
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| 39 |
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| 40 | DH_get_default_method() returns a pointer to the current default DH_METHOD.
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| 41 | However, the meaningfulness of this result is dependent on whether the ENGINE
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| 42 | API is being used, so this function is no longer recommended.
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| 43 |
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| 44 | DH_set_method() selects B<meth> to perform all operations using the key B<dh>.
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| 45 | This will replace the DH_METHOD used by the DH key and if the previous method
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| 46 | was supplied by an ENGINE, the handle to that ENGINE will be released during the
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| 47 | change. It is possible to have DH keys that only work with certain DH_METHOD
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| 48 | implementations (eg. from an ENGINE module that supports embedded
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| 49 | hardware-protected keys), and in such cases attempting to change the DH_METHOD
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| 50 | for the key can have unexpected results.
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| 51 |
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| 52 | DH_new_method() allocates and initializes a DH structure so that B<engine> will
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| 53 | be used for the DH operations. If B<engine> is NULL, the default ENGINE for DH
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| 54 | operations is used, and if no default ENGINE is set, the DH_METHOD controlled by
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| 55 | DH_set_default_method() is used.
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| 56 |
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| 57 | A new DH_METHOD object may be constructed using DH_meth_new() (see
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| 58 | L<DH_meth_new(3)>).
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| 59 |
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| 60 | =head1 RETURN VALUES
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| 61 |
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| 62 | DH_OpenSSL() and DH_get_default_method() return pointers to the respective
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| 63 | B<DH_METHOD>s.
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| 64 |
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| 65 | DH_set_default_method() returns no value.
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| 66 |
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| 67 | DH_set_method() returns non-zero if the provided B<meth> was successfully set as
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| 68 | the method for B<dh> (including unloading the ENGINE handle if the previous
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| 69 | method was supplied by an ENGINE).
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| 70 |
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| 71 | DH_new_method() returns NULL and sets an error code that can be obtained by
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| 72 | L<ERR_get_error(3)> if the allocation fails. Otherwise it
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| 73 | returns a pointer to the newly allocated structure.
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| 74 |
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| 75 | =head1 SEE ALSO
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| 76 |
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| 77 | L<DH_new(3)>, L<DH_new(3)>, L<DH_meth_new(3)>
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| 78 |
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| 79 | =head1 COPYRIGHT
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| 80 |
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| 81 | Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
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| 82 |
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| 83 | Licensed under the OpenSSL license (the "License"). You may not use
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| 84 | this file except in compliance with the License. You can obtain a copy
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| 85 | in the file LICENSE in the source distribution or at
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| 86 | L<https://www.openssl.org/source/license.html>.
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| 87 |
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| 88 | =cut
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