a528d4f0a9
If something was "present in all versions" of SSLeay, or if it was added to a version of SSLeay (and therefore predates OpenSSL), remove mention of it. Documentation history now starts with OpenSSL. Remove mention of all history before OpenSSL 0.9.8, inclusive. Remove all AUTHOR sections. Reviewed-by: Tim Hudson <tjh@openssl.org>
104 lines
3.4 KiB
Text
104 lines
3.4 KiB
Text
=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)> if the allocation fails. Otherwise it
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returns a pointer to the newly allocated structure.
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=head1 SEE ALSO
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L<dh(3)>, L<DH_new(3)>
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=cut
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