plan9port/man/man3/dsa.3

.TH DSA 3
.SH NAME
asn1toDSApriv, dsagen, dsasign, dsaverify, dsapuballoc, dsapubfree, dsaprivalloc, dsaprivfree, dsasigalloc, dsasigfree, dsaprivtopub - digital signature algorithm
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <libc.h>
.br
.B #include <mp.h>
.br
.B #include <libsec.h>
.PP
.B
DSApriv*	dsagen(DSApub *opub)
.PP
.B
DSAsig*	dsasign(DSApriv *k, mpint *m)
.PP
.B
int		dsaverify(DSApub *k, DSAsig *sig, mpint *m)
.PP
.B
DSApub*	dsapuballoc(void)
.PP
.B
void		dsapubfree(DSApub*)
.PP
.B
DSApriv*	dsaprivalloc(void)
.PP
.B
void		dsaprivfree(DSApriv*)
.PP
.B
DSAsig*	dsasigalloc(void)
.PP
.B
void		dsasigfree(DSAsig*)
.PP
.B
DSApub*	dsaprivtopub(DSApriv*)
.PP
.B
DSApriv*	asn1toDSApriv(uchar *priv, int npriv)
.SH DESCRIPTION
.PP
DSA is the NIST approved digital signature algorithm.  The owner of a key publishes
the public part of the key:
.EX
	struct DSApub
	{
		mpint	*p;	// modulus
		mpint	*q;	// group order, q divides p-1
		mpint	*alpha;	// group generator
		mpint	*key;	// alpha**secret mod p
	};
.EE
This part can be used for verifying signatures (with
.IR dsaverify )
created by the owner.
The owner signs (with
.IR dsasign )
using his private key:
.EX
	struct DSApriv
	{
		DSApub	pub;
		mpint	*secret; // (decryption key)
	};
.EE
.PP
Keys are generated using
.IR dsagen .
If
.IR dsagen 's
argument
.I opub
is
.BR nil ,
a key is created using a new
.B p
and
.B q
generated by
.IR DSAprimes
(see
.MR prime (3) ).
Otherwise,
.B p
and
.B q
are copied from the old key.
.PP
.I Dsaprivtopub
returns a newly allocated copy of the public key
corresponding to the private key.
.PP
The routines
.IR dsapuballoc ,
.IR dsapubfree ,
.IR dsaprivalloc ,
and
.I dsaprivfree
are provided to manage key storage.
.PP
.I Dsasign
signs message
.I m
using a private key
.I k
yielding a
.EX
	struct DSAsig
	{
		mpint	*r, *s;
	};
.EE
.I Dsaverify
returns 0 if the signature is valid and \-1 if not.
.PP
The routines
.I dsasigalloc
and
.I dsasigfree
are provided to manage signature storage.
.PP
.I Asn1toDSApriv
converts an ASN1 formatted DSA private key into the corresponding
.B DSApriv
structure; see 
.MR rsa (3)
for other ASN1 routines.
.SH SOURCE
.B \*9/src/libsec
.SH SEE ALSO
.MR mp (3) ,
.MR aes (3) ,
.MR blowfish (3) ,
.MR des (3) ,
.MR rc4 (3) ,
.MR rsa (3) ,
.MR sechash (3) ,
.MR prime (3) ,
.MR rand (3)