=pod

=head1 NAME

dsa - Digital Signature Algorithm

=head1 SYNOPSIS

 #include <openssl/dsa.h>
 #include <openssl/engine.h>

 DSA *  DSA_new(void);
 void   DSA_free(DSA *dsa);

 int    DSA_size(const DSA *dsa);

 DSA *  DSA_generate_parameters(int bits, unsigned char *seed,
                int seed_len, int *counter_ret, unsigned long *h_ret,
                void (*callback)(int, int, void *), void *cb_arg);

 DH *   DSA_dup_DH(const DSA *r);

 int    DSA_generate_key(DSA *dsa);

 int    DSA_sign(int dummy, const unsigned char *dgst, int len,
                unsigned char *sigret, unsigned int *siglen, DSA *dsa);
 int    DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp,
                BIGNUM **rp);
 int    DSA_verify(int dummy, const unsigned char *dgst, int len,
                const unsigned char *sigbuf, int siglen, DSA *dsa);

 void DSA_set_default_method(const DSA_METHOD *meth);
 const DSA_METHOD *DSA_get_default_method(void);
 int DSA_set_method(DSA *dsa, const DSA_METHOD *meth);
 DSA *DSA_new_method(ENGINE *engine);
 const DSA_METHOD *DSA_OpenSSL(void);

 DSA_SIG *DSA_SIG_new(void);
 void   DSA_SIG_free(DSA_SIG *a);
 int    i2d_DSA_SIG(const DSA_SIG *a, unsigned char **pp);
 DSA_SIG *d2i_DSA_SIG(DSA_SIG **v, unsigned char **pp, long length);

 DSA_SIG *DSA_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
 int    DSA_do_verify(const unsigned char *dgst, int dgst_len,
             DSA_SIG *sig, DSA *dsa);

 DSA *  d2i_DSAPublicKey(DSA **a, unsigned char **pp, long length);
 DSA *  d2i_DSAPrivateKey(DSA **a, unsigned char **pp, long length);
 DSA *  d2i_DSAparams(DSA **a, unsigned char **pp, long length);
 int    i2d_DSAPublicKey(const DSA *a, unsigned char **pp);
 int    i2d_DSAPrivateKey(const DSA *a, unsigned char **pp);
 int    i2d_DSAparams(const DSA *a,unsigned char **pp);

 int    DSAparams_print(BIO *bp, const DSA *x);
 int    DSAparams_print_fp(FILE *fp, const DSA *x);
 int    DSA_print(BIO *bp, const DSA *x, int off);
 int    DSA_print_fp(FILE *bp, const DSA *x, int off);

=head1 DESCRIPTION

These functions implement the Digital Signature Algorithm (DSA).  The
generation of shared DSA parameters is described in
L<DSA_generate_parameters(3)>;
L<DSA_generate_key(3)> describes how to
generate a signature key. Signature generation and verification are
described in L<DSA_sign(3)>.

The B<DSA> structure consists of several BIGNUM components.

 struct
        {
        BIGNUM *p;              // prime number (public)
        BIGNUM *q;              // 160-bit subprime, q | p-1 (public)
        BIGNUM *g;              // generator of subgroup (public)
        BIGNUM *priv_key;       // private key x
        BIGNUM *pub_key;        // public key y = g^x
        // ...
        }
 DSA;

In public keys, B<priv_key> is NULL.

Note that DSA keys may use non-standard B<DSA_METHOD> implementations,
either directly or by the use of B<ENGINE> modules. In some cases (eg. an
ENGINE providing support for hardware-embedded keys), these BIGNUM values
will not be used by the implementation or may be used for alternative data
storage. For this reason, applications should generally avoid using DSA
structure elements directly and instead use API functions to query or
modify keys.

=head1 CONFORMING TO

US Federal Information Processing Standard FIPS 186 (Digital Signature
Standard, DSS), ANSI X9.30

=head1 SEE ALSO

L<bn(3)>, L<dh(3)>, L<err(3)>, L<rand(3)>,
L<rsa(3)>, L<sha(3)>, L<engine(3)>,
L<DSA_new(3)>,
L<DSA_size(3)>,
L<DSA_generate_parameters(3)>,
L<DSA_dup_DH(3)>,
L<DSA_generate_key(3)>,
L<DSA_sign(3)>, L<DSA_set_method(3)>,
L<DSA_get_ex_new_index(3)>,
L<RSA_print(3)>

=head1 COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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