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129 lines
4.6 KiB
129 lines
4.6 KiB
=pod |
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=head1 NAME |
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DH_set_default_method, DH_get_default_method, |
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DH_set_method, DH_new_method, DH_OpenSSL - select DH method |
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=head1 SYNOPSIS |
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#include <openssl/dh.h> |
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#include <openssl/engine.h> |
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void DH_set_default_method(const DH_METHOD *meth); |
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const DH_METHOD *DH_get_default_method(void); |
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int DH_set_method(DH *dh, const DH_METHOD *meth); |
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DH *DH_new_method(ENGINE *engine); |
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const DH_METHOD *DH_OpenSSL(void); |
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=head1 DESCRIPTION |
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A B<DH_METHOD> specifies the functions that OpenSSL uses for Diffie-Hellman |
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operations. By modifying the method, alternative implementations |
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such as hardware accelerators may be used. IMPORTANT: See the NOTES section for |
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important information about how these DH API functions are affected by the use |
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of B<ENGINE> API calls. |
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Initially, the default DH_METHOD is the OpenSSL internal implementation, as |
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returned by DH_OpenSSL(). |
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DH_set_default_method() makes B<meth> the default method for all DH |
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structures created later. B<NB>: This is true only whilst no ENGINE has been set |
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as a default for DH, so this function is no longer recommended. |
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DH_get_default_method() returns a pointer to the current default DH_METHOD. |
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However, the meaningfulness of this result is dependent on whether the ENGINE |
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API is being used, so this function is no longer recommended. |
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DH_set_method() selects B<meth> to perform all operations using the key B<dh>. |
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This will replace the DH_METHOD used by the DH key and if the previous method |
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was supplied by an ENGINE, the handle to that ENGINE will be released during the |
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change. It is possible to have DH keys that only work with certain DH_METHOD |
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implementations (eg. from an ENGINE module that supports embedded |
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hardware-protected keys), and in such cases attempting to change the DH_METHOD |
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for the key can have unexpected results. |
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DH_new_method() allocates and initializes a DH structure so that B<engine> will |
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be used for the DH operations. If B<engine> is NULL, the default ENGINE for DH |
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operations is used, and if no default ENGINE is set, the DH_METHOD controlled by |
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DH_set_default_method() is used. |
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=head1 THE DH_METHOD STRUCTURE |
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typedef struct dh_meth_st |
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{ |
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/* name of the implementation */ |
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const char *name; |
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/* generate private and public DH values for key agreement */ |
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int (*generate_key)(DH *dh); |
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/* compute shared secret */ |
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int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh); |
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/* compute r = a ^ p mod m (May be NULL for some implementations) */ |
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int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p, |
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const BIGNUM *m, BN_CTX *ctx, |
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BN_MONT_CTX *m_ctx); |
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/* called at DH_new */ |
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int (*init)(DH *dh); |
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/* called at DH_free */ |
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int (*finish)(DH *dh); |
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int flags; |
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char *app_data; /* ?? */ |
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} DH_METHOD; |
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=head1 RETURN VALUES |
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DH_OpenSSL() and DH_get_default_method() return pointers to the respective |
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B<DH_METHOD>s. |
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DH_set_default_method() returns no value. |
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DH_set_method() returns non-zero if the provided B<meth> was successfully set as |
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the method for B<dh> (including unloading the ENGINE handle if the previous |
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method was supplied by an ENGINE). |
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DH_new_method() returns NULL and sets an error code that can be obtained by |
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L<ERR_get_error(3)|ERR_get_error(3)> if the allocation fails. Otherwise it |
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returns a pointer to the newly allocated structure. |
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=head1 NOTES |
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As of version 0.9.7, DH_METHOD implementations are grouped together with other |
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algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a |
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default ENGINE is specified for DH functionality using an ENGINE API function, |
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that will override any DH defaults set using the DH API (ie. |
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DH_set_default_method()). For this reason, the ENGINE API is the recommended way |
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to control default implementations for use in DH and other cryptographic |
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algorithms. |
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=head1 SEE ALSO |
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L<dh(3)|dh(3)>, L<DH_new(3)|DH_new(3)> |
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=head1 HISTORY |
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DH_set_default_method(), DH_get_default_method(), DH_set_method(), |
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DH_new_method() and DH_OpenSSL() were added in OpenSSL 0.9.4. |
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DH_set_default_openssl_method() and DH_get_default_openssl_method() replaced |
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DH_set_default_method() and DH_get_default_method() respectively, and |
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DH_set_method() and DH_new_method() were altered to use B<ENGINE>s rather than |
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B<DH_METHOD>s during development of the engine version of OpenSSL 0.9.6. For |
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0.9.7, the handling of defaults in the ENGINE API was restructured so that this |
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change was reversed, and behaviour of the other functions resembled more closely |
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the previous behaviour. The behaviour of defaults in the ENGINE API now |
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transparently overrides the behaviour of defaults in the DH API without |
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requiring changing these function prototypes. |
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=cut
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