5bf738737d
docs. There were a couple of other places (including RSA) where the docs were not quite synchronised with the API that are now fixed. One or two still remain to be fixed though ...
143 lines
5.2 KiB
Text
143 lines
5.2 KiB
Text
=pod
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=head1 NAME
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DSA_set_default_method, DSA_get_default_method,
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DSA_set_method, DSA_new_method, DSA_OpenSSL - select DSA method
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=head1 SYNOPSIS
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#include <openssl/dsa.h>
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#include <openssl/engine.h>
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void DSA_set_default_method(const DSA_METHOD *meth);
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const DSA_METHOD *DSA_get_default_method(void);
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int DSA_set_method(DSA *dsa, const DSA_METHOD *meth);
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DSA *DSA_new_method(ENGINE *engine);
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DSA_METHOD *DSA_OpenSSL(void);
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=head1 DESCRIPTION
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A B<DSA_METHOD> specifies the functions that OpenSSL uses for DSA
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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 DSA API functions are affected by the use
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of B<ENGINE> API calls.
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Initially, the default DSA_METHOD is the OpenSSL internal implementation,
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as returned by DSA_OpenSSL().
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DSA_set_default_method() makes B<meth> the default method for all DSA
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structures created later. B<NB>: This is true only whilst no ENGINE has
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been set as a default for DSA, so this function is no longer recommended.
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DSA_get_default_method() returns a pointer to the current default
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DSA_METHOD. However, the meaningfulness of this result is dependant on
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whether the ENGINE API is being used, so this function is no longer
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recommended.
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DSA_set_method() selects B<meth> to perform all operations using the key
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B<rsa>. This will replace the DSA_METHOD used by the DSA key and if the
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previous method was supplied by an ENGINE, the handle to that ENGINE will
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be released during the change. It is possible to have DSA keys that only
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work with certain DSA_METHOD implementations (eg. from an ENGINE module
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that supports embedded hardware-protected keys), and in such cases
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attempting to change the DSA_METHOD for the key can have unexpected
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results.
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DSA_new_method() allocates and initializes a DSA structure so that B<engine>
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will be used for the DSA operations. If B<engine> is NULL, the default engine
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for DSA operations is used, and if no default ENGINE is set, the DSA_METHOD
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controlled by DSA_set_default_method() is used.
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=head1 THE DSA_METHOD STRUCTURE
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struct
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{
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/* name of the implementation */
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const char *name;
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/* sign */
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DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen,
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DSA *dsa);
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/* pre-compute k^-1 and r */
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int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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BIGNUM **rp);
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/* verify */
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int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len,
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DSA_SIG *sig, DSA *dsa);
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/* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some
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implementations) */
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int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1,
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BIGNUM *a2, BIGNUM *p2, BIGNUM *m,
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BN_CTX *ctx, BN_MONT_CTX *in_mont);
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/* compute r = a ^ p mod m (May be NULL for some implementations) */
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int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a,
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const BIGNUM *p, const BIGNUM *m,
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BN_CTX *ctx, BN_MONT_CTX *m_ctx);
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/* called at DSA_new */
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int (*init)(DSA *DSA);
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/* called at DSA_free */
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int (*finish)(DSA *DSA);
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int flags;
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char *app_data; /* ?? */
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} DSA_METHOD;
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=head1 RETURN VALUES
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DSA_OpenSSL() and DSA_get_default_method() return pointers to the respective
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B<DSA_METHOD>s.
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DSA_set_default_method() returns no value.
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DSA_set_method() returns non-zero if the provided B<meth> was successfully set as
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the method for B<dsa> (including unloading the ENGINE handle if the previous
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method was supplied by an ENGINE).
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DSA_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
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fails. Otherwise it returns a pointer to the newly allocated structure.
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=head1 NOTES
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As of version 0.9.7, DSA_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 DSA functionality using an ENGINE API function,
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that will override any DSA defaults set using the DSA API (ie.
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DSA_set_default_method()). For this reason, the ENGINE API is the recommended way
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to control default implementations for use in DSA and other cryptographic
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algorithms.
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=head1 SEE ALSO
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L<dsa(3)|dsa(3)>, L<DSA_new(3)|DSA_new(3)>
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=head1 HISTORY
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DSA_set_default_method(), DSA_get_default_method(), DSA_set_method(),
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DSA_new_method() and DSA_OpenSSL() were added in OpenSSL 0.9.4.
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DSA_set_default_openssl_method() and DSA_get_default_openssl_method() replaced
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DSA_set_default_method() and DSA_get_default_method() respectively, and
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DSA_set_method() and DSA_new_method() were altered to use B<ENGINE>s rather than
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B<DSA_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 DSA API without
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requiring changing these function prototypes.
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=cut
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