ELGAMAL(2)ELGAMAL(2)

NAME

eggen, egencrypt, egdecrypt, egsign, egverify, egpuballoc, egpubfree, egprivalloc, egprivfree, egsigalloc, egsigfree, egprivtopub - elgamal encryption

SYNOPSIS

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

EGpriv* eggen(int nlen, int nrep)

mpint* egencrypt(EGpub *k, mpint *in, mpint *out)

mpint* egdecrypt(EGpriv *k, mpint *in, mpint *out)

EGsig* egsign(EGpriv *k, mpint *m)

int egverify(EGpub *k, EGsig *sig, mpint *m)

EGpub* egpuballoc(void)

void egpubfree(EGpub*)

EGpriv* egprivalloc(void)

void egprivfree(EGpriv*)

EGsig* egsigalloc(void)

void egsigfree(EGsig*)

EGpub* egprivtopub(EGpriv*)

DESCRIPTION

Elgamal is a public key encryption and signature algorithm. The owner of a key publishes the public part of the key: 

	struct EGpub
	{
		mpint	*p;	// modulus
		mpint	*alpha;	// generator
		mpint	*key;	// (encryption key) alpha**secret mod p
	};

This part can be used for encrypting data (with egencrypt) to be sent to the owner. The owner decrypts (with egdecrypt) using his private key: 

	struct EGpriv
	{
		EGpub	pub;
		mpint	*secret; // (decryption key)
	};

Keys are generated using eggen. Eggen takes both bit length of the modulus and the number of repetitions of the Miller-Rabin primality test to run. If the latter is 0, it does the default number of rounds. Egprivtopub returns a newly allocated copy of the public key corresponding to the private key.

The routines egpuballoc, egpubfree, egprivalloc, and egprivfree are provided to manage key storage.

Egsign signs message m using a private key k yielding a 

	struct EGsig
	{
		mpint	*r, *s;
	};

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

The routines egsigalloc and egsigfree are provided to manage signature storage.

SOURCE

/sys/src/libsec

SEE

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