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 dependent 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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