text: =pod
  
  =head1 NAME
  
  DSA_sign, DSA_sign_setup, DSA_verify - DSA signatures
  
  =head1 SYNOPSIS
  
   #include <openssl/dsa.h>
  
   int	DSA_sign(int type, 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 type, const unsigned char *dgst, int len,
  		unsigned char *sigbuf, int siglen, DSA *dsa);
  
  =head1 DESCRIPTION
  
  DSA_sign() computes a digital signature on the B<len> byte message
  digest B<dgst> using the private key B<dsa> and places its ASN.1 DER
  encoding at B<sigret>. The length of the signature is places in
  *B<siglen>. B<sigret> must point to DSA_size(B<dsa>) bytes of memory.
  
  DSA_sign_setup() may be used to precompute part of the signing
  operation in case signature generation is time-critical. It expects
  B<dsa> to contain DSA parameters. It places the precomputed values
  in newly allocated B<BIGNUM>s at *B<kinvp> and *B<rp>, after freeing
  the old ones unless *B<kinvp> and *B<rp> are NULL. These values may
  be passed to DSA_sign() in B<dsa-E<gt>kinv> and B<dsa-E<gt>r>.
  B<ctx> is a pre-allocated B<BN_CTX> or NULL.
  
  DSA_verify() verifies that the signature B<sigbuf> of size B<siglen>
  matches a given message digest B<dgst> of size B<len>.
  B<dsa> is the signer's public key.
  
  The B<type> parameter is ignored.
  
  The PRNG must be seeded before DSA_sign() (or DSA_sign_setup())
  is called.
  
  =head1 RETURN VALUES
  
  DSA_sign() and DSA_sign_setup() return 1 on success, 0 on error.
  DSA_verify() returns 1 for a valid signature, 0 for an incorrect
  signature and -1 on error. The error codes can be obtained by
  L<ERR_get_error(3)|ERR_get_error(3)>.
  
  =head1 CONFORMING TO
  
  US Federal Information Processing Standard FIPS 186 (Digital Signature
  Standard, DSS), ANSI X9.30
  
  =head1 SEE ALSO
  
  L<dsa(3)|dsa(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>,
  L<DSA_do_sign(3)|DSA_do_sign(3)>
  
  =head1 HISTORY
  
  DSA_sign() and DSA_verify() are available in all versions of SSLeay.
  DSA_sign_setup() was added in SSLeay 0.8.
  
  =cut
  