DSAsetmethod(3) OpenSSL DSAsetmethod(3)

NAME
       DSAsetdefaultmethod, DSAgetdefaultmethod, DSAsetmethod,
       DSAnewmethod, DSAOpenSSL - select DSA method

SYNOPSIS
        #include 
        #include 

        void DSAsetdefaultmethod(const DSAMETHOD *meth);

        const DSAMETHOD *DSAgetdefaultmethod(void);

        int DSAsetmethod(DSA *dsa, const DSAMETHOD *meth);

        DSA *DSAnewmethod(ENGINE *engine);

        DSAMETHOD *DSAOpenSSL(void);

DESCRIPTION
       A DDSSAAMMEETTHHOODD specifies the functions that OpenSSL uses for DSA
       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 DSA API functions are
       affected by the use of EENNGGIINNEE API calls.

       Initially, the default DSAMETHOD is the OpenSSL internal
       implementation, as returned by DSAOpenSSL().

       DSAsetdefaultmethod() makes mmeetthh the default method for all DSA
       structures created later. NNBB: This is true only whilst no ENGINE has
       been set as a default for DSA, so this function is no longer
       recommended.

       DSAgetdefaultmethod() returns a pointer to the current default
       DSAMETHOD. However, the meaningfulness of this result is dependant on
       whether the ENGINE API is being used, so this function is no longer
       recommended.

       DSAsetmethod() selects mmeetthh to perform all operations using the key
       rrssaa. This will replace the DSAMETHOD used by the DSA 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 DSA keys
       that only work with certain DSAMETHOD implementations (eg. from an
       ENGINE module that supports embedded hardware-protected keys), and in
       such cases attempting to change the DSAMETHOD for the key can have
       unexpected results.

       DSAnewmethod() allocates and initializes a DSA structure so that
       eennggiinnee will be used for the DSA operations. If eennggiinnee is NULL, the
       default engine for DSA operations is used, and if no default ENGINE is
       set, the DSAMETHOD controlled by DSAsetdefaultmethod() is used.

TTHHEE DDSSAAMMEETTHHOODD SSTTRRUUCCTTUURREE
       struct
        {
            /* name of the implementation */
               const char *name;

            /* sign */
               DSASIG *(*dsadosign)(const unsigned char *dgst, int dlen,
                                        DSA *dsa);

            /* pre-compute k^-1 and r */
               int (*dsasignsetup)(DSA *dsa, BNCTX *ctxin, BIGNUM **kinvp,
                                        BIGNUM **rp);

            /* verify */
               int (*dsadoverify)(const unsigned char *dgst, int dgstlen,
                                        DSASIG *sig, DSA *dsa);

            /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some
                                                 implementations) */
               int (*dsamodexp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1,
                                        BIGNUM *a2, BIGNUM *p2, BIGNUM *m,
                                        BNCTX *ctx, BNMONTCTX *inmont);

            /* compute r = a ^ p mod m (May be NULL for some implementations) */
               int (*bnmodexp)(DSA *dsa, BIGNUM *r, BIGNUM *a,
                                        const BIGNUM *p, const BIGNUM *m,
                                        BNCTX *ctx, BNMONTCTX *mctx);

            /* called at DSAnew */
               int (*init)(DSA *DSA);

            /* called at DSAfree */
               int (*finish)(DSA *DSA);

               int flags;

               char *appdata; /* ?? */

        } DSAMETHOD;

RETURN VALUES
       DSAOpenSSL() and DSAgetdefaultmethod() return pointers to the
       respective DDSSAAMMEETTHHOODDs.

       DSAsetdefaultmethod() returns no value.

       DSAsetmethod() returns non-zero if the provided mmeetthh was successfully
       set as the method for ddssaa (including unloading the ENGINE handle if the
       previous method was supplied by an ENGINE).

       DSAnewmethod() returns NULL and sets an error code that can be
       obtained by ERRgeterror(3) if the allocation fails. Otherwise it
       returns a pointer to the newly allocated structure.

NNOOTTEESS
       As of version 0.9.7, DSAMETHOD implementations are grouped together
       with other algorithmic APIs (eg. RSAMETHOD, EVPCIPHER, etc) in EENNGGIINNEE
       modules. If a default ENGINE is specified for DSA functionality using
       an ENGINE API function, that will override any DSA defaults set using
       the DSA API (ie.  DSAsetdefaultmethod()). For this reason, the
       ENGINE API is the recommended way to control default implementations
       for use in DSA and other cryptographic algorithms.

SEE ALSO
       dsa(3), DSAnew(3)

HISTORY       DSAsetdefaultmethod(), DSAgetdefaultmethod(), DSAsetmethod(),
       DSAnewmethod() and DSAOpenSSL() were added in OpenSSL 0.9.4.

       DSAsetdefaultopensslmethod() and DSAgetdefaultopensslmethod()
       replaced DSAsetdefaultmethod() and DSAgetdefaultmethod()
       respectively, and DSAsetmethod() and DSAnewmethod() were altered to
       use EENNGGIINNEEs rather than DDSSAAMMEETTHHOODDs 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 DSA API
       without requiring changing these function prototypes.



0.9.7l                            2002-10-28                 DSAsetmethod(3)