.\"	$OpenBSD: DSA_set_method.3,v 1.12 2024/05/11 06:53:19 tb Exp $
.\"	OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
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.\" This file was written by Ulf Moeller <ulf@openssl.org>.
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.Dd $Mdocdate: May 11 2024 $
.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.
.Pp
.Fn DSA_get_default_method
returns a pointer to the current default method.
.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.
It is possible to have DSA keys that only work with certain
.Vt DSA_METHOD
implementations,
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.
The
.Fa engine
argument is ignored and
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);
	/* called at DSA_new */
	int (*init)(DSA *DSA);
	/* called at DSA_free */
	int (*finish)(DSA *DSA);
	int flags;
} 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
.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 .