/* Elgamal.c - Elgamal Public Key encryption
* Copyright (C) 1998, 2000, 2001, 2002, 2003,
* 2008 Free Software Foundation, Inc.
* Copyright (C) 2013 g10 Code GmbH
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, see <http://www.gnu.org/licenses/>.
*
* For a description of the algorithm, see:
* Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
* ISBN 0-471-11709-9. Pages 476 ff.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "g10lib.h"
#include "mpi.h"
#include "cipher.h"
#include "pubkey-internal.h"
/* Blinding is used to mitigate side-channel attacks. You may undef
this to speed up the operation in case the system is secured
against physical and network mounted side-channel attacks. */
#define USE_BLINDING 1
typedef struct
{
gcry_mpi_t p; /* prime */
gcry_mpi_t g; /* group generator */
gcry_mpi_t y; /* g^x mod p */
} ELG_public_key;
typedef struct
{
gcry_mpi_t p; /* prime */
gcry_mpi_t g; /* group generator */
gcry_mpi_t y; /* g^x mod p */
gcry_mpi_t x; /* secret exponent */
} ELG_secret_key;
static const char *elg_names[] =
{
"elg",
"openpgp-elg",
"openpgp-elg-sig",
NULL,
};
static int test_keys (ELG_secret_key *sk, unsigned int nbits, int nodie);
static gcry_mpi_t gen_k (gcry_mpi_t p, int small_k);
static gcry_err_code_t generate (ELG_secret_key *sk, unsigned nbits,
gcry_mpi_t **factors);
static int check_secret_key (ELG_secret_key *sk);
static void do_encrypt (gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input,
ELG_public_key *pkey);
static void decrypt (gcry_mpi_t output, gcry_mpi_t a, gcry_mpi_t b,
ELG_secret_key *skey);
static void sign (gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input,
ELG_secret_key *skey);
static int verify (gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input,
ELG_public_key *pkey);
static unsigned int elg_get_nbits (gcry_sexp_t parms);
static void (*progress_cb) (void *, const char *, int, int, int);
static void *progress_cb_data;
void
_gcry_register_pk_elg_progress (void (*cb) (void *, const char *,
int, int, int),
void *cb_data)
{
progress_cb = cb;
progress_cb_data = cb_data;
}
static void
progress (int c)
{
if (progress_cb)
progress_cb (progress_cb_data, "pk_elg", c, 0, 0);
}
/****************
* Michael Wiener's table on subgroup sizes to match field sizes.
* (floating around somewhere, probably based on the paper from
* Eurocrypt 96, page 332)
*/
static unsigned int
wiener_map( unsigned int n )
{
static struct { unsigned int p_n, q_n; } t[] =
{ /* p q attack cost */
{ 512, 119 }, /* 9 x 10^17 */
{ 768, 145 }, /* 6 x 10^21 */
{ 1024, 165 }, /* 7 x 10^24 */
{ 1280, 183 }, /* 3 x 10^27 */
{ 1536, 198 }, /* 7 x 10^29 */
{ 1792, 212 }, /* 9 x 10^31 */
{ 2048, 225 }, /* 8 x 10^33 */
{ 2304, 237 }, /* 5 x 10^35 */
{ 2560, 249 }, /* 3 x 10^37 */
{ 2816, 259 }, /* 1 x 10^39 */
{ 3072, 269 }, /* 3 x 10^40 */
{ 3328, 279 }, /* 8 x 10^41 */
{ 3584, 288 }, /* 2 x 10^43 */
{ 3840, 296 }, /* 4 x 10^44 */
{ 4096, 305 }, /* 7 x 10^45 */
{ 4352, 313 }, /* 1 x 10^47 */
{ 4608, 320 }, /* 2 x 10^48 */
{ 4864, 328 }, /* 2 x 10^49 */
{ 5120, 335 }, /* 3 x 10^50 */
{ 0, 0 }
};
int i;
for(i=0; t[i].p_n; i++ )
{
if( n <= t[i].p_n )
return t[i].q_n;
}
/* Not in table - use an arbitrary high number. */
return n / 8 + 200;
}
static int
test_keys ( ELG_secret_key *sk, unsigned int nbits, int nodie )
{
ELG_public_key pk;
gcry_mpi_t test = mpi_new ( 0 );
gcry_mpi_t out1_a = mpi_new ( nbits );
gcry_mpi_t out1_b = mpi_new ( nbits );
gcry_mpi_t out2 = mpi_new ( nbits );
int failed = 0;
pk.p = sk->p;
pk.g = sk->g;
pk.y = sk->y;
_gcry_mpi_randomize ( test, nbits, GCRY_WEAK_RANDOM );
do_encrypt ( out1_a, out1_b, test, &pk );
decrypt ( out2, out1_a, out1_b, sk );
if ( mpi_cmp( test, out2 ) )
failed |= 1;
sign ( out1_a, out1_b, test, sk );
if ( !verify( out1_a, out1_b, test, &pk ) )
failed |= 2;
_gcry_mpi_release ( test );
_gcry_mpi_release ( out1_a );
_gcry_mpi_release ( out1_b );
_gcry_mpi_release ( out2 );
if (failed && !nodie)
log_fatal ("Elgamal test key for %s %s failed\n",
(failed & 1)? "encrypt+decrypt":"",
(failed & 2)? "sign+verify":"");
if (failed && DBG_CIPHER)
log_debug ("Elgamal test key for %s %s failed\n",
(failed & 1)? "encrypt+decrypt":"",
(failed & 2)? "sign+verify":"");
return failed;
}
/****************
* Generate a random secret exponent k from prime p, so that k is
* relatively prime to p-1. With SMALL_K set, k will be selected for
* better encryption performance - this must never be used signing!
*/
static gcry_mpi_t
gen_k( gcry_mpi_t p, int small_k )
{
gcry_mpi_t k = mpi_alloc_secure( 0 );
gcry_mpi_t temp = mpi_alloc( mpi_get_nlimbs(p) );
gcry_mpi_t p_1 = mpi_copy(p);
unsigned int orig_nbits = mpi_get_nbits(p);
unsigned int nbits, nbytes;
char *rndbuf = NULL;
if (small_k)
{
/* Using a k much lesser than p is sufficient for encryption and
* it greatly improves the encryption performance. We use
* Wiener's table and add a large safety margin. */
nbits = wiener_map( orig_nbits ) * 3 / 2;
if( nbits >= orig_nbits )
BUG();
}
else
nbits = orig_nbits;
nbytes = (nbits+7)/8;
if( DBG_CIPHER )
log_debug("choosing a random k\n");
mpi_sub_ui( p_1, p, 1);
for(;;)
{
if( !rndbuf || nbits < 32 )
{
xfree(rndbuf);
rndbuf = _gcry_random_bytes_secure( nbytes, GCRY_STRONG_RANDOM );
}
else
{
/* Change only some of the higher bits. We could improve
this by directly requesting more memory at the first call
to get_random_bytes() and use this the here maybe it is
easier to do this directly in random.c Anyway, it is
highly inlikely that we will ever reach this code. */
char *pp = _gcry_random_bytes_secure( 4, GCRY_STRONG_RANDOM );
memcpy( rndbuf, pp, 4 );
xfree(pp);
}
_gcry_mpi_set_buffer( k, rndbuf, nbytes, 0 );
for(;;)
{
if( !(mpi_cmp( k, p_1 ) < 0) ) /* check: k < (p-1) */
{
if( DBG_CIPHER )
progress('+');
break; /* no */
}
if( !(mpi_cmp_ui( k, 0 ) > 0) ) /* check: k > 0 */
{
if( DBG_CIPHER )
progress('-');
break; /* no */
}
if (mpi_gcd( temp, k, p_1 ))
goto found; /* okay, k is relative prime to (p-1) */
mpi_add_ui( k, k, 1 );
if( DBG_CIPHER )
progress('.');
}
}
found:
xfree (rndbuf);
if( DBG_CIPHER )
progress('\n');
mpi_free(p_1);
mpi_free(temp);
return k;
}
/****************
* Generate a key pair with a key of size NBITS
* Returns: 2 structures filled with all needed values
* and an array with n-1 factors of (p-1)
*/
static gcry_err_code_t
generate ( ELG_secret_key *sk, unsigned int nbits, gcry_mpi_t **ret_factors )
{
gcry_err_code_t rc;
gcry_mpi_t p; /* the prime */
gcry_mpi_t p_min1;
gcry_mpi_t g;
gcry_mpi_t x; /* the secret exponent */
gcry_mpi_t y;
unsigned int qbits;
unsigned int xbits;
byte *rndbuf;
p_min1 = mpi_new ( nbits );
qbits = wiener_map( nbits );
if( qbits & 1 ) /* better have a even one */
qbits++;
g = mpi_alloc(1);
rc = _gcry_generate_elg_prime (0, nbits, qbits, g, &p, ret_factors);
if (rc)
{
mpi_free (p_min1);
mpi_free (g);
return rc;
}
mpi_sub_ui(p_min1, p, 1);
/* Select a random number which has these properties:
* 0 < x < p-1
* This must be a very good random number because this is the
* secret part. The prime is public and may be shared anyway,
* so a random generator level of 1 is used for the prime.
*
* I don't see a reason to have a x of about the same size
* as the p. It should be sufficient to have one about the size
* of q or the later used k plus a large safety margin. Decryption
* will be much faster with such an x.
*/
xbits = qbits * 3 / 2;
if( xbits >= nbits )
BUG();
x = mpi_snew ( xbits );
if( DBG_CIPHER )
log_debug("choosing a random x of size %u\n", xbits );
rndbuf = NULL;
do
{
if( DBG_CIPHER )
progress('.');
if( rndbuf )
{ /* Change only some of the higher bits */
if( xbits < 16 ) /* should never happen ... */
{
xfree(rndbuf);
rndbuf = _gcry_random_bytes_secure ((xbits+7)/8,
GCRY_VERY_STRONG_RANDOM);
}
else
{
char *r = _gcry_random_bytes_secure (2, GCRY_VERY_STRONG_RANDOM);
memcpy(rndbuf, r, 2 );
xfree (r);
}
}
else
{
rndbuf = _gcry_random_bytes_secure ((xbits+7)/8,
GCRY_VERY_STRONG_RANDOM );
}
_gcry_mpi_set_buffer( x, rndbuf, (xbits+7)/8, 0 );
mpi_clear_highbit( x, xbits+1 );
}
while( !( mpi_cmp_ui( x, 0 )>0 && mpi_cmp( x, p_min1 )<0 ) );
xfree(rndbuf);
y = mpi_new (nbits);
mpi_powm( y, g, x, p );
if( DBG_CIPHER )
{
progress ('\n');
log_mpidump ("elg p", p );
log_mpidump ("elg g", g );
log_mpidump ("elg y", y );
log_mpidump ("elg x", x );
}
/* Copy the stuff to the key structures */
sk->p = p;
sk->g = g;
sk->y = y;
sk->x = x;
_gcry_mpi_release ( p_min1 );
/* Now we can test our keys (this should never fail!) */
test_keys ( sk, nbits - 64, 0 );
return 0;
}
/* Generate a key pair with a key of size NBITS not using a random
value for the secret key but the one given as X. This is useful to
implement a passphrase based decryption for a public key based
encryption. It has appliactions in backup systems.
Returns: A structure filled with all needed values and an array
with n-1 factors of (p-1). */
static gcry_err_code_t
generate_using_x (ELG_secret_key *sk, unsigned int nbits, gcry_mpi_t x,
gcry_mpi_t **ret_factors )
{
gcry_err_code_t rc;
gcry_mpi_t p; /* The prime. */
gcry_mpi_t p_min1; /* The prime minus 1. */
gcry_mpi_t g; /* The generator. */
gcry_mpi_t y; /* g^x mod p. */
unsigned int qbits;
unsigned int xbits;
sk->p = NULL;
sk->g = NULL;
sk->y = NULL;
sk->x = NULL;
/* Do a quick check to see whether X is suitable. */
xbits = mpi_get_nbits (x);
if ( xbits < 64 || xbits >= nbits )
return GPG_ERR_INV_VALUE;
p_min1 = mpi_new ( nbits );
qbits = wiener_map ( nbits );
if ( (qbits & 1) ) /* Better have an even one. */
qbits++;
g = mpi_alloc (1);
rc = _gcry_generate_elg_prime (0, nbits, qbits, g, &p, ret_factors );
if (rc)
{
mpi_free (p_min1);
mpi_free (g);
return rc;
}
mpi_sub_ui (p_min1, p, 1);
if (DBG_CIPHER)
log_debug ("using a supplied x of size %u", xbits );
if ( !(mpi_cmp_ui ( x, 0 ) > 0 && mpi_cmp ( x, p_min1 ) <0 ) )
{
_gcry_mpi_release ( p_min1 );
_gcry_mpi_release ( p );
_gcry_mpi_release ( g );
return GPG_ERR_INV_VALUE;
}
y = mpi_new (nbits);
mpi_powm ( y, g, x, p );
if ( DBG_CIPHER )
{
progress ('\n');
log_mpidump ("elg p", p );
log_mpidump ("elg g", g );
log_mpidump ("elg y", y );
log_mpidump ("elg x", x );
}
/* Copy the stuff to the key structures */
sk->p = p;
sk->g = g;
sk->y = y;
sk->x = mpi_copy (x);
_gcry_mpi_release ( p_min1 );
/* Now we can test our keys. */
if ( test_keys ( sk, nbits - 64, 1 ) )
{
_gcry_mpi_release ( sk->p ); sk->p = NULL;
_gcry_mpi_release ( sk->g ); sk->g = NULL;
_gcry_mpi_release ( sk->y ); sk->y = NULL;
_gcry_mpi_release ( sk->x ); sk->x = NULL;
return GPG_ERR_BAD_SECKEY;
}
return 0;
}
/****************
* Test whether the secret key is valid.
* Returns: if this is a valid key.
*/
static int
check_secret_key( ELG_secret_key *sk )
{
int rc;
gcry_mpi_t y = mpi_alloc( mpi_get_nlimbs(sk->y) );
mpi_powm (y, sk->g, sk->x, sk->p);
rc = !mpi_cmp( y, sk->y );
mpi_free( y );
return rc;
}
static void
do_encrypt(gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input, ELG_public_key *pkey )
{
gcry_mpi_t k;
/* Note: maybe we should change the interface, so that it
* is possible to check that input is < p and return an
* error code.
*/
k = gen_k( pkey->p, 1 );
mpi_powm (a, pkey->g, k, pkey->p);
/* b = (y^k * input) mod p
* = ((y^k mod p) * (input mod p)) mod p
* and because input is < p
* = ((y^k mod p) * input) mod p
*/
mpi_powm (b, pkey->y, k, pkey->p);
mpi_mulm (b, b, input, pkey->p);
#if 0
if( DBG_CIPHER )
{
log_mpidump("elg encrypted y", pkey->y);
log_mpidump("elg encrypted p", pkey->p);
log_mpidump("elg encrypted k", k);
log_mpidump("elg encrypted M", input);
log_mpidump("elg encrypted a", a);
log_mpidump("elg encrypted b", b);
}
#endif
mpi_free(k);
}
static void
decrypt (gcry_mpi_t output, gcry_mpi_t a, gcry_mpi_t b, ELG_secret_key *skey )
{
gcry_mpi_t t1, t2, r;
unsigned int nbits = mpi_get_nbits (skey->p);
mpi_normalize (a);
mpi_normalize (b);
t1 = mpi_snew (nbits);
#ifdef USE_BLINDING
t2 = mpi_snew (nbits);
r = mpi_new (nbits);
/* We need a random number of about the prime size. The random
number merely needs to be unpredictable; thus we use level 0. */
_gcry_mpi_randomize (r, nbits, GCRY_WEAK_RANDOM);
/* t1 = r^x mod p */
mpi_powm (t1, r, skey->x, skey->p);
/* t2 = (a * r)^-x mod p */
mpi_mulm (t2, a, r, skey->p);
mpi_powm (t2, t2, skey->x, skey->p);
mpi_invm (t2, t2, skey->p);
/* t1 = (t1 * t2) mod p*/
mpi_mulm (t1, t1, t2, skey->p);
mpi_free (r);
mpi_free (t2);
#else /*!USE_BLINDING*/
/* output = b/(a^x) mod p */
mpi_powm (t1, a, skey->x, skey->p);
mpi_invm (t1, t1, skey->p);
#endif /*!USE_BLINDING*/
mpi_mulm (output, b, t1, skey->p);
#if 0
if( DBG_CIPHER )
{
log_mpidump ("elg decrypted x", skey->x);
log_mpidump ("elg decrypted p", skey->p);
log_mpidump ("elg decrypted a", a);
log_mpidump ("elg decrypted b", b);
log_mpidump ("elg decrypted M", output);
}
#endif
mpi_free (t1);
}
/****************
* Make an Elgamal signature out of INPUT
*/
static void
sign(gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input, ELG_secret_key *skey )
{
gcry_mpi_t k;
gcry_mpi_t t = mpi_alloc( mpi_get_nlimbs(a) );
gcry_mpi_t inv = mpi_alloc( mpi_get_nlimbs(a) );
gcry_mpi_t p_1 = mpi_copy(skey->p);
/*
* b = (t * inv) mod (p-1)
* b = (t * inv(k,(p-1),(p-1)) mod (p-1)
* b = (((M-x*a) mod (p-1)) * inv(k,(p-1),(p-1))) mod (p-1)
*
*/
mpi_sub_ui(p_1, p_1, 1);
k = gen_k( skey->p, 0 /* no small K ! */ );
mpi_powm( a, skey->g, k, skey->p );
mpi_mul(t, skey->x, a );
mpi_subm(t, input, t, p_1 );
mpi_invm(inv, k, p_1 );
mpi_mulm(b, t, inv, p_1 );
#if 0
if( DBG_CIPHER )
{
log_mpidump ("elg sign p", skey->p);
log_mpidump ("elg sign g", skey->g);
log_mpidump ("elg sign y", skey->y);
log_mpidump ("elg sign x", skey->x);
log_mpidump ("elg sign k", k);
log_mpidump ("elg sign M", input);
log_mpidump ("elg sign a", a);
log_mpidump ("elg sign b", b);
}
#endif
mpi_free(k);
mpi_free(t);
mpi_free(inv);
mpi_free(p_1);
}
/****************
* Returns true if the signature composed of A and B is valid.
*/
static int
verify(gcry_mpi_t a, gcry_mpi_t b, gcry_mpi_t input, ELG_public_key *pkey )
{
int rc;
gcry_mpi_t t1;
gcry_mpi_t t2;
gcry_mpi_t base[4];
gcry_mpi_t ex[4];
if( !(mpi_cmp_ui( a, 0 ) > 0 && mpi_cmp( a, pkey->p ) < 0) )
return 0; /* assertion 0 < a < p failed */
t1 = mpi_alloc( mpi_get_nlimbs(a) );
t2 = mpi_alloc( mpi_get_nlimbs(a) );
#if 0
/* t1 = (y^a mod p) * (a^b mod p) mod p */
gcry_mpi_powm( t1, pkey->y, a, pkey->p );
gcry_mpi_powm( t2, a, b, pkey->p );
mpi_mulm( t1, t1, t2, pkey->p );
/* t2 = g ^ input mod p */
gcry_mpi_powm( t2, pkey->g, input, pkey->p );
rc = !mpi_cmp( t1, t2 );
#elif 0
/* t1 = (y^a mod p) * (a^b mod p) mod p */
base[0] = pkey->y; ex[0] = a;
base[1] = a; ex[1] = b;
base[2] = NULL; ex[2] = NULL;
mpi_mulpowm( t1, base, ex, pkey->p );
/* t2 = g ^ input mod p */
gcry_mpi_powm( t2, pkey->g, input, pkey->p );
rc = !mpi_cmp( t1, t2 );
#else
/* t1 = g ^ - input * y ^ a * a ^ b mod p */
mpi_invm(t2, pkey->g, pkey->p );
base[0] = t2 ; ex[0] = input;
base[1] = pkey->y; ex[1] = a;
base[2] = a; ex[2] = b;
base[3] = NULL; ex[3] = NULL;
mpi_mulpowm( t1, base, ex, pkey->p );
rc = !mpi_cmp_ui( t1, 1 );
#endif
mpi_free(t1);
mpi_free(t2);
return rc;
}
/*********************************************
************** interface ******************
*********************************************/
static gpg_err_code_t
elg_generate (const gcry_sexp_t genparms, gcry_sexp_t *r_skey)
{
gpg_err_code_t rc;
unsigned int nbits;
ELG_secret_key sk;
gcry_mpi_t xvalue = NULL;
gcry_sexp_t l1;
gcry_mpi_t *factors = NULL;
gcry_sexp_t misc_info = NULL;
memset (&sk, 0, sizeof sk);
rc = _gcry_pk_util_get_nbits (genparms, &nbits);
if (rc)
return rc;
/* Parse the optional xvalue element. */
l1 = sexp_find_token (genparms, "xvalue", 0);
if (l1)
{
xvalue = sexp_nth_mpi (l1, 1, 0);
sexp_release (l1);
if (!xvalue)
return GPG_ERR_BAD_MPI;
}
if (xvalue)
{
rc = generate_using_x (&sk, nbits, xvalue, &factors);
mpi_free (xvalue);
}
else
{
rc = generate (&sk, nbits, &factors);
}
if (rc)
goto leave;
if (factors && factors[0])
{
int nfac;
void **arg_list;
char *buffer, *p;
for (nfac = 0; factors[nfac]; nfac++)
;
arg_list = xtrycalloc (nfac+1, sizeof *arg_list);
if (!arg_list)
{
rc = gpg_err_code_from_syserror ();
goto leave;
}
buffer = xtrymalloc (30 + nfac*2 + 2 + 1);
if (!buffer)
{
rc = gpg_err_code_from_syserror ();
xfree (arg_list);
goto leave;
}
p = stpcpy (buffer, "(misc-key-info(pm1-factors");
for(nfac = 0; factors[nfac]; nfac++)
{
p = stpcpy (p, "%m");
arg_list[nfac] = factors + nfac;
}
p = stpcpy (p, "))");
rc = sexp_build_array (&misc_info, NULL, buffer, arg_list);
xfree (arg_list);
xfree (buffer);
if (rc)
goto leave;
}
rc = sexp_build (r_skey, NULL,
"(key-data"
" (public-key"
" (elg(p%m)(g%m)(y%m)))"
" (private-key"
" (elg(p%m)(g%m)(y%m)(x%m)))"
" %S)",
sk.p, sk.g, sk.y,
sk.p, sk.g, sk.y, sk.x,
misc_info);
leave:
mpi_free (sk.p);
mpi_free (sk.g);
mpi_free (sk.y);
mpi_free (sk.x);
sexp_release (misc_info);
if (factors)
{
gcry_mpi_t *mp;
for (mp = factors; *mp; mp++)
mpi_free (*mp);
xfree (factors);
}
return rc;
}
static gcry_err_code_t
elg_check_secret_key (gcry_sexp_t keyparms)
{
gcry_err_code_t rc;
ELG_secret_key sk = {NULL, NULL, NULL, NULL};
rc = sexp_extract_param (keyparms, NULL, "pgyx",
&sk.p, &sk.g, &sk.y, &sk.x,
NULL);
if (rc)
goto leave;
if (!check_secret_key (&sk))
rc = GPG_ERR_BAD_SECKEY;
leave:
_gcry_mpi_release (sk.p);
_gcry_mpi_release (sk.g);
_gcry_mpi_release (sk.y);
_gcry_mpi_release (sk.x);
if (DBG_CIPHER)
log_debug ("elg_testkey => %s\n", gpg_strerror (rc));
return rc;
}
static gcry_err_code_t
elg_encrypt (gcry_sexp_t *r_ciph, gcry_sexp_t s_data, gcry_sexp_t keyparms)
{
gcry_err_code_t rc;
struct pk_encoding_ctx ctx;
gcry_mpi_t mpi_a = NULL;
gcry_mpi_t mpi_b = NULL;
gcry_mpi_t data = NULL;
ELG_public_key pk = { NULL, NULL, NULL };
_gcry_pk_util_init_encoding_ctx (&ctx, PUBKEY_OP_ENCRYPT,
elg_get_nbits (keyparms));
/* Extract the data. */
rc = _gcry_pk_util_data_to_mpi (s_data, &data, &ctx);
if (rc)
goto leave;
if (DBG_CIPHER)
log_mpidump ("elg_encrypt data", data);
if (mpi_is_opaque (data))
{
rc = GPG_ERR_INV_DATA;
goto leave;
}
/* Extract the key. */
rc = sexp_extract_param (keyparms, NULL, "pgy",
&pk.p, &pk.g, &pk.y, NULL);
if (rc)
goto leave;
if (DBG_CIPHER)
{
log_mpidump ("elg_encrypt p", pk.p);
log_mpidump ("elg_encrypt g", pk.g);
log_mpidump ("elg_encrypt y", pk.y);
}
/* Do Elgamal computation and build result. */
mpi_a = mpi_new (0);
mpi_b = mpi_new (0);
do_encrypt (mpi_a, mpi_b, data, &pk);
rc = sexp_build (r_ciph, NULL, "(enc-val(elg(a%m)(b%m)))", mpi_a, mpi_b);
leave:
_gcry_mpi_release (mpi_a);
_gcry_mpi_release (mpi_b);
_gcry_mpi_release (pk.p);
_gcry_mpi_release (pk.g);
_gcry_mpi_release (pk.y);
_gcry_mpi_release (data);
_gcry_pk_util_free_encoding_ctx (&ctx);
if (DBG_CIPHER)
log_debug ("elg_encrypt => %s\n", gpg_strerror (rc));
return rc;
}
static gcry_err_code_t
elg_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
{
gpg_err_code_t rc;
struct pk_encoding_ctx ctx;
gcry_sexp_t l1 = NULL;
gcry_mpi_t data_a = NULL;
gcry_mpi_t data_b = NULL;
ELG_secret_key sk = {NULL, NULL, NULL, NULL};
gcry_mpi_t plain = NULL;
unsigned char *unpad = NULL;
size_t unpadlen = 0;
_gcry_pk_util_init_encoding_ctx (&ctx, PUBKEY_OP_DECRYPT,
elg_get_nbits (keyparms));
/* Extract the data. */
rc = _gcry_pk_util_preparse_encval (s_data, elg_names, &l1, &ctx);
if (rc)
goto leave;
rc = sexp_extract_param (l1, NULL, "ab", &data_a, &data_b, NULL);
if (rc)
goto leave;
if (DBG_CIPHER)
{
log_printmpi ("elg_decrypt d_a", data_a);
log_printmpi ("elg_decrypt d_b", data_b);
}
if (mpi_is_opaque (data_a) || mpi_is_opaque (data_b))
{
rc = GPG_ERR_INV_DATA;
goto leave;
}
/* Extract the key. */
rc = sexp_extract_param (keyparms, NULL, "pgyx",
&sk.p, &sk.g, &sk.y, &sk.x,
NULL);
if (rc)
goto leave;
if (DBG_CIPHER)
{
log_printmpi ("elg_decrypt p", sk.p);
log_printmpi ("elg_decrypt g", sk.g);
log_printmpi ("elg_decrypt y", sk.y);
if (!fips_mode ())
log_printmpi ("elg_decrypt x", sk.x);
}
plain = mpi_snew (ctx.nbits);
decrypt (plain, data_a, data_b, &sk);
if (DBG_CIPHER)
log_printmpi ("elg_decrypt res", plain);
/* Reverse the encoding and build the s-expression. */
switch (ctx.encoding)
{
case PUBKEY_ENC_PKCS1:
rc = _gcry_rsa_pkcs1_decode_for_enc (&unpad, &unpadlen, ctx.nbits, plain);
mpi_free (plain); plain = NULL;
if (!rc)
rc = sexp_build (r_plain, NULL, "(value %b)", (int)unpadlen, unpad);
break;
case PUBKEY_ENC_OAEP:
rc = _gcry_rsa_oaep_decode (&unpad, &unpadlen,
ctx.nbits, ctx.hash_algo, plain,
ctx.label, ctx.labellen);
mpi_free (plain); plain = NULL;
if (!rc)
rc = sexp_build (r_plain, NULL, "(value %b)", (int)unpadlen, unpad);
break;
default:
/* Raw format. For backward compatibility we need to assume a
signed mpi by using the sexp format string "%m". */
rc = sexp_build (r_plain, NULL,
(ctx.flags & PUBKEY_FLAG_LEGACYRESULT)
? "%m" : "(value %m)",
plain);
break;
}
leave:
xfree (unpad);
_gcry_mpi_release (plain);
_gcry_mpi_release (sk.p);
_gcry_mpi_release (sk.g);
_gcry_mpi_release (sk.y);
_gcry_mpi_release (sk.x);
_gcry_mpi_release (data_a);
_gcry_mpi_release (data_b);
sexp_release (l1);
_gcry_pk_util_free_encoding_ctx (&ctx);
if (DBG_CIPHER)
log_debug ("elg_decrypt => %s\n", gpg_strerror (rc));
return rc;
}
static gcry_err_code_t
elg_sign (gcry_sexp_t *r_sig, gcry_sexp_t s_data, gcry_sexp_t keyparms)
{
gcry_err_code_t rc;
struct pk_encoding_ctx ctx;
gcry_mpi_t data = NULL;
ELG_secret_key sk = {NULL, NULL, NULL, NULL};
gcry_mpi_t sig_r = NULL;
gcry_mpi_t sig_s = NULL;
_gcry_pk_util_init_encoding_ctx (&ctx, PUBKEY_OP_SIGN,
elg_get_nbits (keyparms));
/* Extract the data. */
rc = _gcry_pk_util_data_to_mpi (s_data, &data, &ctx);
if (rc)
goto leave;
if (DBG_CIPHER)
log_mpidump ("elg_sign data", data);
if (mpi_is_opaque (data))
{
rc = GPG_ERR_INV_DATA;
goto leave;
}
/* Extract the key. */
rc = sexp_extract_param (keyparms, NULL, "pgyx",
&sk.p, &sk.g, &sk.y, &sk.x, NULL);
if (rc)
goto leave;
if (DBG_CIPHER)
{
log_mpidump ("elg_sign p", sk.p);
log_mpidump ("elg_sign g", sk.g);
log_mpidump ("elg_sign y", sk.y);
if (!fips_mode ())
log_mpidump ("elg_sign x", sk.x);
}
sig_r = mpi_new (0);
sig_s = mpi_new (0);
sign (sig_r, sig_s, data, &sk);
if (DBG_CIPHER)
{
log_mpidump ("elg_sign sig_r", sig_r);
log_mpidump ("elg_sign sig_s", sig_s);
}
rc = sexp_build (r_sig, NULL, "(sig-val(elg(r%M)(s%M)))", sig_r, sig_s);
leave:
_gcry_mpi_release (sig_r);
_gcry_mpi_release (sig_s);
_gcry_mpi_release (sk.p);
_gcry_mpi_release (sk.g);
_gcry_mpi_release (sk.y);
_gcry_mpi_release (sk.x);
_gcry_mpi_release (data);
_gcry_pk_util_free_encoding_ctx (&ctx);
if (DBG_CIPHER)
log_debug ("elg_sign => %s\n", gpg_strerror (rc));
return rc;
}
static gcry_err_code_t
elg_verify (gcry_sexp_t s_sig, gcry_sexp_t s_data, gcry_sexp_t s_keyparms)
{
gcry_err_code_t rc;
struct pk_encoding_ctx ctx;
gcry_sexp_t l1 = NULL;
gcry_mpi_t sig_r = NULL;
gcry_mpi_t sig_s = NULL;
gcry_mpi_t data = NULL;
ELG_public_key pk = { NULL, NULL, NULL };
_gcry_pk_util_init_encoding_ctx (&ctx, PUBKEY_OP_VERIFY,
elg_get_nbits (s_keyparms));
/* Extract the data. */
rc = _gcry_pk_util_data_to_mpi (s_data, &data, &ctx);
if (rc)
goto leave;
if (DBG_CIPHER)
log_mpidump ("elg_verify data", data);
if (mpi_is_opaque (data))
{
rc = GPG_ERR_INV_DATA;
goto leave;
}
/* Extract the signature value. */
rc = _gcry_pk_util_preparse_sigval (s_sig, elg_names, &l1, NULL);
if (rc)
goto leave;
rc = sexp_extract_param (l1, NULL, "rs", &sig_r, &sig_s, NULL);
if (rc)
goto leave;
if (DBG_CIPHER)
{
log_mpidump ("elg_verify s_r", sig_r);
log_mpidump ("elg_verify s_s", sig_s);
}
/* Extract the key. */
rc = sexp_extract_param (s_keyparms, NULL, "pgy",
&pk.p, &pk.g, &pk.y, NULL);
if (rc)
goto leave;
if (DBG_CIPHER)
{
log_mpidump ("elg_verify p", pk.p);
log_mpidump ("elg_verify g", pk.g);
log_mpidump ("elg_verify y", pk.y);
}
/* Verify the signature. */
if (!verify (sig_r, sig_s, data, &pk))
rc = GPG_ERR_BAD_SIGNATURE;
leave:
_gcry_mpi_release (pk.p);
_gcry_mpi_release (pk.g);
_gcry_mpi_release (pk.y);
_gcry_mpi_release (data);
_gcry_mpi_release (sig_r);
_gcry_mpi_release (sig_s);
sexp_release (l1);
_gcry_pk_util_free_encoding_ctx (&ctx);
if (DBG_CIPHER)
log_debug ("elg_verify => %s\n", rc?gpg_strerror (rc):"Good");
return rc;
}
/* Return the number of bits for the key described by PARMS. On error
* 0 is returned. The format of PARMS starts with the algorithm name;
* for example:
*
* (dsa
* (p <mpi>)
* (g <mpi>)
* (y <mpi>))
*
* More parameters may be given but we only need P here.
*/
static unsigned int
elg_get_nbits (gcry_sexp_t parms)
{
gcry_sexp_t l1;
gcry_mpi_t p;
unsigned int nbits;
l1 = sexp_find_token (parms, "p", 1);
if (!l1)
return 0; /* Parameter P not found. */
p= sexp_nth_mpi (l1, 1, GCRYMPI_FMT_USG);
sexp_release (l1);
nbits = p? mpi_get_nbits (p) : 0;
_gcry_mpi_release (p);
return nbits;
}
gcry_pk_spec_t _gcry_pubkey_spec_elg =
{
GCRY_PK_ELG, { 0, 0 },
(GCRY_PK_USAGE_SIGN | GCRY_PK_USAGE_ENCR),
"ELG", elg_names,
"pgy", "pgyx", "ab", "rs", "pgy",
elg_generate,
elg_check_secret_key,
elg_encrypt,
elg_decrypt,
elg_sign,
elg_verify,
elg_get_nbits,
};