.\" $OpenBSD: DSA_set_method.3,v 1.6 2016/12/10 22:47:49 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: December 10 2016 $ .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 .In openssl/engine.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 specifies the functions that OpenSSL uses for DSA operations. By modifying the method, alternative implementations such as hardware accelerators may be used. See the .Sx CAVEATS section for how these DSA API functions are affected by the use of .Xr engine 3 API calls. .Pp Initially, the default .Vt DSA_METHOD is the OpenSSL internal implementation, as returned by .Fn DSA_OpenSSL . .Pp .Fn DSA_set_default_method makes .Fa meth the default method for all .Vt DSA structures created later. .Sy Note : this is true only whilst no .Vt ENGINE has been set as a default for DSA, so this function is no longer recommended. .Pp .Fn DSA_get_default_method returns a pointer to the current default .Vt DSA_METHOD . However, the meaningfulness of this result is dependent on whether the .Xr engine 3 API is being used, so this function is no longer recommended. .Pp .Fn DSA_set_method selects .Fa meth to perform all operations using the key .Fa dsa . This will replace the .Vt DSA_METHOD used by the DSA key and if the previous method was supplied by an .Vt ENGINE , the handle to that .Vt ENGINE will be released during the change. 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 will be used for the DSA operations. If .Fa engine is .Dv NULL , the default engine for DSA operations is used and, if no default .Vt ENGINE is set, the .Vt DSA_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 Ns s . .Pp .Fn DSA_set_method returns non-zero if the provided .Fa meth was successfully set as the method for .Fa dsa (including unloading the .Vt ENGINE handle if the previous method was supplied by an .Vt ENGINE ) . .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_new 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 were added in OpenSSL 0.9.4. .Sh CAVEATS As of version 0.9.7, DSA_METHOD implementations are grouped together with other algorithmic APIs (e.g. RSA_METHOD, EVP_CIPHER) in .Vt ENGINE modules. If a default .Vt ENGINE is specified for DSA functionality using an .Xr engine 3 API function, that will override any DSA defaults set using the DSA API .Pq i.e. DSA_set_default_method . For this reason, the .Xr engine 3 API is the recommended way to control default implementations for use in DSA and other cryptographic algorithms.