NAME
dsagen, dsasign, dsaverify, dsapuballoc, dsapubfree, dsaprivalloc, dsaprivfree, dsasigalloc, dsasigfree, dsaprivtopub – digital signature algorithm

SYNOPSIS
#include <u.h>
#include <libc.h>
#include <mp.h>
#include <libsec.h>

DSApriv*    dsagen(DSApub *opub)

DSAsig*     dsasign(DSApriv *k, mpint *m)

int         dsaverify(DSApub *k, DSAsig *sig, mpint *m)

DSApub*     dsapuballoc(void)

void        dsapubfree(DSApub*)

DSApriv*    dsaprivalloc(void)

void        dsaprivfree(DSApriv*)

DSAsig*     dsasigalloc(void)

void        dsasigfree(DSAsig*)

DSApub*     dsaprivtopub(DSApriv*)

DESCRIPTION

DSA is the NIST approved digital signature algorithm. The owner of a key publishes the public part of the key:
struct DSApub
{
mpint       *p;    // modulus
mpint       *q;    // group order, q divides p–1
mpint       *alpha;     // group generator
mpint       *key;       // alpha**secret mod p
};

This part can be used for verifying signatures (with dsaverify) created by the owner. The owner signs (with dsasign) using his private key:
struct DSApriv
{
DSApub      pub;
mpint       *secret; // (decryption key)
};

Keys are generated using dsagen. If dsagen's argument opub is nil, a key is created using a new p and q generated by DSAprimes (see prime(2)). Otherwise, p and q are copied from the old key.

Dsaprivtopub returns a newly allocated copy of the public key corresponding to the private key.

The routines dsapuballoc, dsapubfree, dsaprivalloc, and dsaprivfree are provided to manage key storage.

Dsasign signs message m using a private key k yielding a
struct DSAsig
{
mpint       *r, *s;
};

Dsaverify returns 0 if the signature is valid and –1 if not.

The routines dsasigalloc and dsasigfree are provided to manage signature storage.

SOURCE
/sys/src/libsec

SEE ALSO
mp(2), aes(2), blowfish(2), des(2), rc4(2), rsa(2), sechash(2), prime(2), rand(2), dsa(8)
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