.\" $OpenBSD: DSA_set_method.3,v 1.9 2018/04/18 01:09:01 schwarze Exp $ .\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 .\" .\" This file was written by Ulf Moeller . .\" Copyright (c) 2000, 2002, 2007 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: April 18 2018 $ .Dt DSA_SET_METHOD 3 .Os .Sh NAME .Nm DSA_set_default_method , .Nm DSA_get_default_method , .Nm DSA_set_method , .Nm DSA_new_method , .Nm DSA_OpenSSL .Nd select DSA method .Sh SYNOPSIS .In openssl/dsa.h .Ft void .Fo DSA_set_default_method .Fa "const DSA_METHOD *meth" .Fc .Ft const DSA_METHOD * .Fn DSA_get_default_method void .Ft int .Fo DSA_set_method .Fa "DSA *dsa" .Fa "const DSA_METHOD *meth" .Fc .Ft DSA * .Fo DSA_new_method .Fa "ENGINE *engine" .Fc .Ft DSA_METHOD * .Fn DSA_OpenSSL void .Sh DESCRIPTION A .Vt DSA_METHOD object contains pointers to the functions used for DSA operations. By default, the internal implementation returned by .Fn DSA_OpenSSL is used. By selecting another method, alternative implementations such as hardware accelerators may be used. .Pp .Fn DSA_set_default_method selects .Fa meth as the default method for all .Vt DSA structures created later. If any .Vt ENGINE was registered with .Xr ENGINE_register_DSA 3 that can be successfully initialized, it overrides the default. .Pp .Fn DSA_get_default_method returns a pointer to the current default method, even if it is actually overridded by an .Vt ENGINE . .Pp .Fn DSA_set_method selects .Fa meth to perform all operations using the key .Fa dsa . This replaces the .Vt DSA_METHOD used by the DSA key and if the previous method was supplied by an .Vt ENGINE , .Xr ENGINE_finish 3 is called on it. It is possible to have DSA keys that only work with certain .Vt DSA_METHOD implementations (e.g. from an .Vt ENGINE module that supports embedded hardware-protected keys), and in such cases attempting to change the .Vt DSA_METHOD for the key can have unexpected results. .Pp .Fn DSA_new_method allocates and initializes a .Vt DSA structure so that .Fa engine is used for the DSA operations. If .Fa engine is .Dv NULL , .Xr ENGINE_get_default_DSA 3 is used. If that returns .Dv NULL , the default method controlled by .Fn DSA_set_default_method is used. .Pp The .Vt DSA_METHOD structure is defined as follows: .Bd -literal struct { /* name of the implementation */ const char *name; /* sign */ DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen, DSA *dsa); /* pre-compute k^-1 and r */ int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp); /* verify */ int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, DSA *dsa); /* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some implementations) */ int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1, BIGNUM *a2, BIGNUM *p2, BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *in_mont); /* compute r = a ^ p mod m (May be NULL for some implementations) */ int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx); /* called at DSA_new */ int (*init)(DSA *DSA); /* called at DSA_free */ int (*finish)(DSA *DSA); int flags; char *app_data; /* ?? */ } DSA_METHOD; .Ed .Sh RETURN VALUES .Fn DSA_OpenSSL and .Fn DSA_get_default_method return pointers to the respective .Vt DSA_METHOD . .Pp .Fn DSA_set_method returns 1 on success or 0 on failure. Currently, it cannot fail. .Pp .Fn DSA_new_method returns .Dv NULL and sets an error code that can be obtained by .Xr ERR_get_error 3 if the allocation fails. Otherwise it returns a pointer to the newly allocated structure. .Sh SEE ALSO .Xr DSA_meth_new 3 , .Xr DSA_new 3 , .Xr ENGINE_get_default_DSA 3 , .Xr ENGINE_register_DSA 3 , .Xr ENGINE_set_default_DSA 3 .Sh HISTORY .Fn DSA_set_default_method , .Fn DSA_get_default_method , .Fn DSA_set_method , .Fn DSA_new_method , and .Fn DSA_OpenSSL first appeared in OpenSSL 0.9.5 and have been available since .Ox 2.7 .