111 lines
3.5 KiB
Text
111 lines
3.5 KiB
Text
=pod
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=head1 NAME
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DH_set_default_openssl_method, DH_get_default_openssl_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_openssl_method(DH_METHOD *meth);
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DH_METHOD *DH_get_default_openssl_method(void);
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int DH_set_method(DH *dh, ENGINE *engine);
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DH *DH_new_method(ENGINE *engine);
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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.
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Initially, the default is to use the OpenSSL internal implementation.
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DH_OpenSSL() returns a pointer to that method.
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DH_set_default_openssl_method() makes B<meth> the default method for all DH
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structures created later. B<NB:> This is true only whilst the default engine
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for Diffie-Hellman operations remains as "openssl". ENGINEs provide an
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encapsulation for implementations of one or more algorithms, and all the DH
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functions mentioned here operate within the scope of the default
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"openssl" engine.
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DH_get_default_openssl_method() returns a pointer to the current default
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method for the "openssl" engine.
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DH_set_method() selects B<engine> as the engine that will be responsible for
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all operations using the structure B<dh>. If this function completes successfully,
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then the B<dh> structure will have its own functional reference of B<engine>, so
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the caller should remember to free their own reference to B<engine> when they are
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finished with it. NB: An ENGINE's DH_METHOD can be retrieved (or set) by
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ENGINE_get_DH() or ENGINE_set_DH().
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DH_new_method() allocates and initializes a DH structure so that
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B<engine> will be used for the DH operations. If B<engine> is NULL,
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the default engine for Diffie-Hellman opertaions 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_openssl_method() return pointers to the
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respective B<DH_METHOD>s.
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DH_set_default_openssl_method() returns no value.
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DH_set_method() returns non-zero if the ENGINE associated with B<dh>
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was successfully changed to B<engine>.
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DH_new_method() returns NULL and sets an error code that can be
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obtained by L<ERR_get_error(3)|ERR_get_error(3)> if the allocation fails.
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Otherwise it returns a pointer to the newly allocated structure.
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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()
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replaced DH_set_default_method() and DH_get_default_method() respectively,
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and DH_set_method() and DH_new_method() were altered to use B<ENGINE>s
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rather than B<DH_METHOD>s during development of OpenSSL 0.9.6.
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=cut
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