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Diffstat (limited to 'openssl/doc/crypto/DH_set_method.pod')
-rw-r--r-- | openssl/doc/crypto/DH_set_method.pod | 129 |
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diff --git a/openssl/doc/crypto/DH_set_method.pod b/openssl/doc/crypto/DH_set_method.pod new file mode 100644 index 0000000..d5cdc3b --- /dev/null +++ b/openssl/doc/crypto/DH_set_method.pod @@ -0,0 +1,129 @@ +=pod + +=head1 NAME + +DH_set_default_method, DH_get_default_method, +DH_set_method, DH_new_method, DH_OpenSSL - select DH method + +=head1 SYNOPSIS + + #include <openssl/dh.h> + #include <openssl/engine.h> + + void DH_set_default_method(const DH_METHOD *meth); + + const DH_METHOD *DH_get_default_method(void); + + int DH_set_method(DH *dh, const DH_METHOD *meth); + + DH *DH_new_method(ENGINE *engine); + + const DH_METHOD *DH_OpenSSL(void); + +=head1 DESCRIPTION + +A B<DH_METHOD> specifies the functions that OpenSSL uses for Diffie-Hellman +operations. By modifying the method, alternative implementations +such as hardware accelerators may be used. IMPORTANT: See the NOTES section for +important information about how these DH API functions are affected by the use +of B<ENGINE> API calls. + +Initially, the default DH_METHOD is the OpenSSL internal implementation, as +returned by DH_OpenSSL(). + +DH_set_default_method() makes B<meth> the default method for all DH +structures created later. B<NB>: This is true only whilst no ENGINE has been set +as a default for DH, so this function is no longer recommended. + +DH_get_default_method() returns a pointer to the current default DH_METHOD. +However, the meaningfulness of this result is dependent on whether the ENGINE +API is being used, so this function is no longer recommended. + +DH_set_method() selects B<meth> to perform all operations using the key B<dh>. +This will replace the DH_METHOD used by the DH key and if the previous method +was supplied by an ENGINE, the handle to that ENGINE will be released during the +change. It is possible to have DH keys that only work with certain DH_METHOD +implementations (eg. from an ENGINE module that supports embedded +hardware-protected keys), and in such cases attempting to change the DH_METHOD +for the key can have unexpected results. + +DH_new_method() allocates and initializes a DH structure so that B<engine> will +be used for the DH operations. If B<engine> is NULL, the default ENGINE for DH +operations is used, and if no default ENGINE is set, the DH_METHOD controlled by +DH_set_default_method() is used. + +=head1 THE DH_METHOD STRUCTURE + + typedef struct dh_meth_st + { + /* name of the implementation */ + const char *name; + + /* generate private and public DH values for key agreement */ + int (*generate_key)(DH *dh); + + /* compute shared secret */ + int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh); + + /* compute r = a ^ p mod m (May be NULL for some implementations) */ + int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p, + const BIGNUM *m, BN_CTX *ctx, + BN_MONT_CTX *m_ctx); + + /* called at DH_new */ + int (*init)(DH *dh); + + /* called at DH_free */ + int (*finish)(DH *dh); + + int flags; + + char *app_data; /* ?? */ + + } DH_METHOD; + +=head1 RETURN VALUES + +DH_OpenSSL() and DH_get_default_method() return pointers to the respective +B<DH_METHOD>s. + +DH_set_default_method() returns no value. + +DH_set_method() returns non-zero if the provided B<meth> was successfully set as +the method for B<dh> (including unloading the ENGINE handle if the previous +method was supplied by an ENGINE). + +DH_new_method() returns NULL and sets an error code that can be obtained by +L<ERR_get_error(3)|ERR_get_error(3)> if the allocation fails. Otherwise it +returns a pointer to the newly allocated structure. + +=head1 NOTES + +As of version 0.9.7, DH_METHOD implementations are grouped together with other +algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a +default ENGINE is specified for DH functionality using an ENGINE API function, +that will override any DH defaults set using the DH API (ie. +DH_set_default_method()). For this reason, the ENGINE API is the recommended way +to control default implementations for use in DH and other cryptographic +algorithms. + +=head1 SEE ALSO + +L<dh(3)|dh(3)>, L<DH_new(3)|DH_new(3)> + +=head1 HISTORY + +DH_set_default_method(), DH_get_default_method(), DH_set_method(), +DH_new_method() and DH_OpenSSL() were added in OpenSSL 0.9.4. + +DH_set_default_openssl_method() and DH_get_default_openssl_method() replaced +DH_set_default_method() and DH_get_default_method() respectively, and +DH_set_method() and DH_new_method() were altered to use B<ENGINE>s rather than +B<DH_METHOD>s during development of the engine version of OpenSSL 0.9.6. For +0.9.7, the handling of defaults in the ENGINE API was restructured so that this +change was reversed, and behaviour of the other functions resembled more closely +the previous behaviour. The behaviour of defaults in the ENGINE API now +transparently overrides the behaviour of defaults in the DH API without +requiring changing these function prototypes. + +=cut |