| DSA(3) | DSA(3)

NAME

| asn1toDSApriv, 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*)

` `DSApriv* asn1toDSApriv(uchar *priv, int npriv)
`

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(3)). 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.

Asn1toDSApriv converts an ASN1 formatted DSA private key into the corresponding `DSApriv` structure; see rsa(3) for other ASN1 routines.

SOURCE

| `/usr/local/plan9/src/libsec`

SEE ALSO

| mp(3), aes(3), blowfish(3), des(3), rc4(3), rsa(3), sechash(3), prime(3), rand(3)