mpi_alloc_like( MPI a )
#endif
{
MPI b;
if( a && (a->flags & 4) ) {
void *p = m_is_secure(a->d)? xmalloc_secure( a->nbits )
: xmalloc( a->nbits );
memcpy( p, a->d, a->nbits );
b = mpi_set_opaque( NULL, p, a->nbits );
}
else if( a ) {
#ifdef M_DEBUG
b = mpi_is_secure(a)? mpi_debug_alloc_secure( a->nlimbs, info )
: mpi_debug_alloc( a->nlimbs, info );
#else
b = mpi_is_secure(a)? mpi_alloc_secure( a->nlimbs )
: mpi_alloc( a->nlimbs );
#endif
b->nlimbs = 0;
b->sign = 0;
b->flags = a->flags;
b->nbits = 0;
}
else
b = NULL;
return b;
}
/****************
* Note: This copy function should not interpret the MPI
* but copy it transparently.
*/
gcry_mpi_t
gcry_mpi_copy( gcry_mpi_t a )
{
int i;
gcry_mpi_t b;
if( a && (a->flags & 4) ) {
void *p = gcry_is_secure(a->d)? gcry_xmalloc_secure( (a->sign+7)/8 )
: gcry_xmalloc( (a->sign+7)/8 );
memcpy( p, a->d, (a->sign+7)/8 );
b = gcry_mpi_set_opaque( NULL, p, a->sign );
}
else if( a ) {
b = mpi_is_secure(a)? mpi_alloc_secure( a->nlimbs )
: mpi_alloc( a->nlimbs );
b->nlimbs = a->nlimbs;
b->sign = a->sign;
b->flags = a->flags;
for(i=0; i < b->nlimbs; i++ )
b->d[i] = a->d[i];
}
else
b = NULL;
return b;
}
/****************
* Note: This copy function should not interpret the MPI
* but copy it transparently.
*/
gcry_mpi_t
_gcry_mpi_copy (gcry_mpi_t a)
{
int i;
gcry_mpi_t b;
if( a && (a->flags & 4) ) {
void *p = _gcry_is_secure(a->d)? xmalloc_secure ((a->sign+7)/8)
: xmalloc ((a->sign+7)/8);
memcpy( p, a->d, (a->sign+7)/8 );
b = mpi_set_opaque( NULL, p, a->sign );
b->flags &= ~(16|32); /* Reset the immutable and constant flags. */
}
else if( a ) {
b = mpi_is_secure(a)? mpi_alloc_secure( a->nlimbs )
: mpi_alloc( a->nlimbs );
b->nlimbs = a->nlimbs;
b->sign = a->sign;
b->flags = a->flags;
b->flags &= ~(16|32); /* Reset the immutable and constant flags. */
for(i=0; i < b->nlimbs; i++ )
b->d[i] = a->d[i];
}
else
b = NULL;
return b;
}
mpi_copy_gpg( MPI a )
#endif
{
int i;
MPI b;
if( a && (a->flags & 4) ) {
void *p = m_is_secure(a->d)? xmalloc_secure( a->nbits )
: xmalloc( a->nbits );
memcpy( p, a->d, a->nbits );
b = mpi_set_opaque( NULL, p, a->nbits );
}
else if( a ) {
#ifdef M_DEBUG
b = mpi_is_secure(a)? mpi_debug_alloc_secure( a->nlimbs, info )
: mpi_debug_alloc( a->nlimbs, info );
#else
b = mpi_is_secure(a)? mpi_alloc_secure( a->nlimbs )
: mpi_alloc( a->nlimbs );
#endif
b->nlimbs = a->nlimbs;
b->sign = a->sign;
b->flags = a->flags;
b->nbits = a->nbits;
for(i=0; i < b->nlimbs; i++ )
b->d[i] = a->d[i];
}
else
b = NULL;
return b;
}
MPI
mpi_read_from_buffer(byte *buffer, unsigned int *ret_nread, int secure)
{
int i, j;
unsigned nbits, nbytes, nlimbs, nread=0;
mpi_limb_t a;
MPI val = NULL;
if( *ret_nread < 2 )
goto leave;
nbits = buffer[0] << 8 | buffer[1];
if( nbits > MAX_EXTERN_MPI_BITS ) {
log_info ("mpi too large (%u bits)\n", nbits);
goto leave;
}
buffer += 2;
nread = 2;
nbytes = (nbits+7) / 8;
nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
val = secure? mpi_alloc_secure( nlimbs )
: mpi_alloc( nlimbs );
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
val->nbits = nbits;
j= val->nlimbs = nlimbs;
val->sign = 0;
for( ; j > 0; j-- ) {
a = 0;
for(; i < BYTES_PER_MPI_LIMB; i++ ) {
if( ++nread > *ret_nread ) {
/* This (as well as the above error condition) may
happen if we use this function to parse a decrypted
MPI which didn't turn out to be a real MPI - possible
because the supplied key was wrong but the OpenPGP
checksum didn't caught it. */
log_info ("mpi larger than buffer\n");
mpi_free (val);
val = NULL;
goto leave;
}
a <<= 8;
a |= *buffer++;
}
i = 0;
val->d[j-1] = a;
}
leave:
*ret_nread = nread;
return val;
}
mpi_read(IOBUF inp, unsigned *ret_nread, int secure)
#endif
{
int c, i, j;
unsigned nbits, nbytes, nlimbs, nread=0;
mpi_limb_t a;
MPI val = MPI_NULL;
if( (c = iobuf_get(inp)) == -1 )
goto leave;
nbits = c << 8;
if( (c = iobuf_get(inp)) == -1 )
goto leave;
nbits |= c;
if( nbits > MAX_EXTERN_MPI_BITS ) {
log_error("mpi too large (%u bits)\n", nbits);
goto leave;
}
nread = 2;
nbytes = (nbits+7) / 8;
nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
#ifdef M_DEBUG
val = secure? mpi_debug_alloc_secure( nlimbs, info )
: mpi_debug_alloc( nlimbs, info );
#else
val = secure? mpi_alloc_secure( nlimbs )
: mpi_alloc( nlimbs );
#endif
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
val->nbits = nbits;
j= val->nlimbs = nlimbs;
val->sign = 0;
for( ; j > 0; j-- ) {
a = 0;
for(; i < BYTES_PER_MPI_LIMB; i++ ) {
a <<= 8;
a |= iobuf_get(inp) & 0xff; nread++;
}
i = 0;
val->d[j-1] = a;
}
leave:
if( nread > *ret_nread )
log_bug("mpi crosses packet border\n");
else
*ret_nread = nread;
return val;
}
/* Helper used to scan PGP style MPIs. Returns NULL on failure. */
static gcry_mpi_t
mpi_read_from_buffer (const unsigned char *buffer, unsigned *ret_nread,
int secure)
{
int i, j;
unsigned int nbits, nbytes, nlimbs, nread=0;
mpi_limb_t a;
gcry_mpi_t val = MPI_NULL;
if ( *ret_nread < 2 )
goto leave;
nbits = buffer[0] << 8 | buffer[1];
if ( nbits > MAX_EXTERN_MPI_BITS )
{
/* log_debug ("mpi too large (%u bits)\n", nbits); */
goto leave;
}
buffer += 2;
nread = 2;
nbytes = (nbits+7) / 8;
nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
val = secure? mpi_alloc_secure (nlimbs) : mpi_alloc (nlimbs);
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
j= val->nlimbs = nlimbs;
val->sign = 0;
for ( ; j > 0; j-- )
{
a = 0;
for (; i < BYTES_PER_MPI_LIMB; i++ )
{
if ( ++nread > *ret_nread )
{
/* log_debug ("mpi larger than buffer"); */
mpi_free (val);
val = NULL;
goto leave;
}
a <<= 8;
a |= *buffer++;
}
i = 0;
val->d[j-1] = a;
}
leave:
*ret_nread = nread;
return val;
}
int
elg_decrypt( int algo, MPI *result, MPI *data, MPI *skey )
{
ELG_secret_key sk;
if( !is_ELGAMAL(algo) )
return G10ERR_PUBKEY_ALGO;
if( !data[0] || !data[1]
|| !skey[0] || !skey[1] || !skey[2] || !skey[3] )
return G10ERR_BAD_MPI;
sk.p = skey[0];
sk.g = skey[1];
sk.y = skey[2];
sk.x = skey[3];
*result = mpi_alloc_secure( mpi_get_nlimbs( sk.p ) );
decrypt( *result, data[0], data[1], &sk );
return 0;
}
MPI
mpi_read_from_buffer(byte *buffer, unsigned *ret_nread, int secure)
{
int i, j;
unsigned nbits, nbytes, nlimbs, nread=0;
mpi_limb_t a;
MPI val = MPI_NULL;
if( *ret_nread < 2 )
goto leave;
nbits = buffer[0] << 8 | buffer[1];
if( nbits > MAX_EXTERN_MPI_BITS ) {
log_error("mpi too large (%u bits)\n", nbits);
goto leave;
}
buffer += 2;
nread = 2;
nbytes = (nbits+7) / 8;
nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
val = secure? mpi_alloc_secure( nlimbs )
: mpi_alloc( nlimbs );
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
val->nbits = nbits;
j= val->nlimbs = nlimbs;
val->sign = 0;
for( ; j > 0; j-- ) {
a = 0;
for(; i < BYTES_PER_MPI_LIMB; i++ ) {
if( ++nread > *ret_nread )
log_bug("mpi larger than buffer\n");
a <<= 8;
a |= *buffer++;
}
i = 0;
val->d[j-1] = a;
}
leave:
*ret_nread = nread;
return val;
}
static void
decrypt(gcry_mpi_t output, gcry_mpi_t a, gcry_mpi_t b, ELG_secret_key *skey )
{
gcry_mpi_t t1 = mpi_alloc_secure( mpi_get_nlimbs( skey->p ) );
/* output = b/(a^x) mod p */
gcry_mpi_powm( t1, a, skey->x, skey->p );
mpi_invm( t1, t1, skey->p );
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);
}
/****************
* This function allocates an MPI which is optimized to hold
* a value as large as the one given in the argument and allocates it
* with the same flags as A.
*/
gcry_mpi_t
_gcry_mpi_alloc_like( gcry_mpi_t a )
{
gcry_mpi_t b;
if( a && (a->flags & 4) ) {
int n = (a->sign+7)/8;
void *p = _gcry_is_secure(a->d)? xtrymalloc_secure (n)
: xtrymalloc (n);
memcpy( p, a->d, n );
b = mpi_set_opaque( NULL, p, a->sign );
}
else if( a ) {
b = mpi_is_secure(a)? mpi_alloc_secure( a->nlimbs )
: mpi_alloc( a->nlimbs );
b->nlimbs = 0;
b->sign = 0;
b->flags = a->flags;
}
else
b = NULL;
return b;
}
gcry_err_code_t
_gcry_elg_decrypt (int algo, gcry_mpi_t *result,
gcry_mpi_t *data, gcry_mpi_t *skey, int flags)
{
gcry_err_code_t err = GPG_ERR_NO_ERROR;
ELG_secret_key sk;
(void)algo;
(void)flags;
if ((! data[0]) || (! data[1])
|| (! skey[0]) || (! skey[1]) || (! skey[2]) || (! skey[3]))
err = GPG_ERR_BAD_MPI;
else
{
sk.p = skey[0];
sk.g = skey[1];
sk.y = skey[2];
sk.x = skey[3];
*result = mpi_alloc_secure (mpi_get_nlimbs (sk.p));
decrypt (*result, data[0], data[1], &sk);
}
return err;
}
/****************
* Generate a key pair with a key of size NBITS
* Returns: 2 structures filles with all needed values
* and an array with n-1 factors of (p-1)
*/
static void
generate( ELG_secret_key *sk, unsigned int nbits, MPI **ret_factors )
{
MPI p; /* the prime */
MPI p_min1;
MPI g;
MPI x; /* the secret exponent */
MPI y;
MPI temp;
unsigned int qbits;
unsigned int xbits;
byte *rndbuf;
p_min1 = mpi_alloc ( mpi_nlimb_hint_from_nbits (nbits) );
temp = mpi_alloc ( mpi_nlimb_hint_from_nbits (nbits) );
qbits = wiener_map ( nbits );
if( qbits & 1 ) /* better have a even one */
qbits++;
g = mpi_alloc(1);
p = generate_elg_prime( 0, nbits, qbits, g, ret_factors );
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. Note that this is not optimal for
* signing keys becuase it makes an attack using accidential small
* K values even easier. Well, one should not use ElGamal signing
* anyway.
*/
xbits = qbits * 3 / 2;
if( xbits >= nbits )
BUG();
x = mpi_alloc_secure ( mpi_nlimb_hint_from_nbits (xbits) );
if( DBG_CIPHER )
log_debug("choosing a random x of size %u", 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 = get_random_bits( xbits, 2, 1 );
}
else {
char *r = get_random_bits( 16, 2, 1 );
memcpy(rndbuf, r, 16/8 );
xfree(r);
}
}
else
rndbuf = get_random_bits( xbits, 2, 1 );
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_alloc ( mpi_nlimb_hint_from_nbits (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;
/* now we can test our keys (this should never fail!) */
test_keys( sk, nbits - 64 );
mpi_free( p_min1 );
mpi_free( temp );
}
static MPI
gen_prime( unsigned nbits, int secret, int randomlevel )
{
unsigned nlimbs;
MPI prime, ptest, pminus1, val_2, val_3, result;
int i;
unsigned x, step;
unsigned count1, count2;
int *mods;
if( 0 && DBG_CIPHER )
log_debug("generate a prime of %u bits ", nbits );
if( !no_of_small_prime_numbers ) {
for(i=0; small_prime_numbers[i]; i++ )
no_of_small_prime_numbers++;
}
mods = m_alloc( no_of_small_prime_numbers * sizeof *mods );
/* make nbits fit into MPI implementation */
nlimbs = (nbits + BITS_PER_MPI_LIMB - 1) / BITS_PER_MPI_LIMB;
val_2 = mpi_alloc_set_ui( 2 );
val_3 = mpi_alloc_set_ui( 3);
prime = secret? mpi_alloc_secure( nlimbs ): mpi_alloc( nlimbs );
result = mpi_alloc_like( prime );
pminus1= mpi_alloc_like( prime );
ptest = mpi_alloc_like( prime );
count1 = count2 = 0;
for(;;) { /* try forvever */
int dotcount=0;
/* generate a random number */
{ char *p = get_random_bits( nbits, randomlevel, secret );
mpi_set_buffer( prime, p, (nbits+7)/8, 0 );
m_free(p);
}
/* set high order bit to 1, set low order bit to 1 */
mpi_set_highbit( prime, nbits-1 );
mpi_set_bit( prime, 0 );
/* calculate all remainders */
for(i=0; (x = small_prime_numbers[i]); i++ )
mods[i] = mpi_fdiv_r_ui(NULL, prime, x);
/* now try some primes starting with prime */
for(step=0; step < 20000; step += 2 ) {
/* check against all the small primes we have in mods */
count1++;
for(i=0; (x = small_prime_numbers[i]); i++ ) {
while( mods[i] + step >= x )
mods[i] -= x;
if( !(mods[i] + step) )
break;
}
if( x )
continue; /* found a multiple of an already known prime */
mpi_add_ui( ptest, prime, step );
/* do a faster Fermat test */
count2++;
mpi_sub_ui( pminus1, ptest, 1);
mpi_powm( result, val_2, pminus1, ptest );
if( !mpi_cmp_ui( result, 1 ) ) { /* not composite */
/* perform stronger tests */
if( is_prime(ptest, 5, &count2 ) ) {
if( !mpi_test_bit( ptest, nbits-1 ) ) {
progress('\n');
log_debug("overflow in prime generation\n");
break; /* step loop, continue with a new prime */
}
mpi_free(val_2);
mpi_free(val_3);
mpi_free(result);
mpi_free(pminus1);
mpi_free(prime);
m_free(mods);
return ptest;
}
}
if( ++dotcount == 10 ) {
progress('.');
dotcount = 0;
}
}
progress(':'); /* restart with a new random value */
}
}
/****************
* 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 ");
mpi_sub_ui( p_1, p, 1);
for(;;)
{
if( !rndbuf || nbits < 32 )
{
gcry_free(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 );
gcry_free(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 (gcry_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:
gcry_free(rndbuf);
if( DBG_CIPHER )
progress('\n');
mpi_free(p_1);
mpi_free(temp);
return k;
}
/* Convert the external representation of an integer stored in BUFFER
with a length of BUFLEN into a newly create MPI returned in
RET_MPI. If NBYTES is not NULL, it will receive the number of
bytes actually scanned after a successful operation. */
gcry_error_t
gcry_mpi_scan (struct gcry_mpi **ret_mpi, enum gcry_mpi_format format,
const void *buffer_arg, size_t buflen, size_t *nscanned)
{
const unsigned char *buffer = (const unsigned char*)buffer_arg;
struct gcry_mpi *a = NULL;
unsigned int len;
int secure = (buffer && gcry_is_secure (buffer));
if (format == GCRYMPI_FMT_SSH)
len = 0;
else
len = buflen;
if (format == GCRYMPI_FMT_STD)
{
const unsigned char *s = buffer;
a = secure? mpi_alloc_secure ((len+BYTES_PER_MPI_LIMB-1)
/BYTES_PER_MPI_LIMB)
: mpi_alloc ((len+BYTES_PER_MPI_LIMB-1)/BYTES_PER_MPI_LIMB);
if (len)
{
a->sign = !!(*s & 0x80);
if (a->sign)
{
/* FIXME: we have to convert from 2compl to magnitude format */
mpi_free (a);
return gcry_error (GPG_ERR_INTERNAL);
}
else
_gcry_mpi_set_buffer (a, s, len, 0);
}
if (ret_mpi)
{
mpi_normalize ( a );
*ret_mpi = a;
}
else
mpi_free(a);
return 0;
}
else if (format == GCRYMPI_FMT_USG)
{
a = secure? mpi_alloc_secure ((len+BYTES_PER_MPI_LIMB-1)
/BYTES_PER_MPI_LIMB)
: mpi_alloc ((len+BYTES_PER_MPI_LIMB-1)/BYTES_PER_MPI_LIMB);
if (len)
_gcry_mpi_set_buffer (a, buffer, len, 0);
if (ret_mpi)
{
mpi_normalize ( a );
*ret_mpi = a;
}
else
mpi_free(a);
return 0;
}
else if (format == GCRYMPI_FMT_PGP)
{
a = mpi_read_from_buffer (buffer, &len, secure);
if (nscanned)
*nscanned = len;
if (ret_mpi && a)
{
mpi_normalize (a);
*ret_mpi = a;
}
else if (a)
{
mpi_free(a);
a = NULL;
}
return a? 0 : gcry_error (GPG_ERR_INV_OBJ);
}
else if (format == GCRYMPI_FMT_SSH)
{
const unsigned char *s = buffer;
size_t n;
/* This test is not strictly necessary and an assert (!len)
would be sufficient. We keep this test in case we later
allow the BUFLEN argument to act as a sanitiy check. Same
below. */
if (len && len < 4)
return gcry_error (GPG_ERR_TOO_SHORT);
n = (s[0] << 24 | s[1] << 16 | s[2] << 8 | s[3]);
s += 4;
if (len)
len -= 4;
if (len && n > len)
return gcry_error (GPG_ERR_TOO_LARGE);
a = secure? mpi_alloc_secure ((n+BYTES_PER_MPI_LIMB-1)
/BYTES_PER_MPI_LIMB)
: mpi_alloc ((n+BYTES_PER_MPI_LIMB-1)/BYTES_PER_MPI_LIMB);
if (n)
{
a->sign = !!(*s & 0x80);
if (a->sign)
{
/* FIXME: we have to convert from 2compl to magnitude format */
mpi_free(a);
return gcry_error (GPG_ERR_INTERNAL);
}
else
_gcry_mpi_set_buffer( a, s, n, 0 );
}
if (nscanned)
*nscanned = n+4;
if (ret_mpi)
{
mpi_normalize ( a );
*ret_mpi = a;
}
else
mpi_free(a);
return 0;
}
else if (format == GCRYMPI_FMT_HEX)
{
/* We can only handle C strings for now. */
if (buflen)
return gcry_error (GPG_ERR_INV_ARG);
a = secure? mpi_alloc_secure (0) : mpi_alloc(0);
if (mpi_fromstr (a, (const char *)buffer))
{
mpi_free (a);
return gcry_error (GPG_ERR_INV_OBJ);
}
if (ret_mpi)
{
mpi_normalize ( a );
*ret_mpi = a;
}
else
mpi_free(a);
return 0;
}
else
return gcry_error (GPG_ERR_INV_ARG);
}
mpi_read(IOBUF inp, unsigned *ret_nread, int secure)
#endif
{
int c, i, j;
unsigned int nmax = *ret_nread;
unsigned nbits, nbytes, nlimbs, nread=0;
mpi_limb_t a;
MPI val = NULL;
if (nread == nmax)
goto overflow;
if( (c = iobuf_get(inp)) == -1 )
goto leave;
nread++;
nbits = c << 8;
if (nread == nmax)
goto overflow;
if( (c = iobuf_get(inp)) == -1 )
goto leave;
nread++;
nbits |= c;
if( nbits > MAX_EXTERN_MPI_BITS ) {
log_error("mpi too large for this implementation (%u bits)\n", nbits);
goto leave;
}
nbytes = (nbits+7) / 8;
nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
#ifdef M_DEBUG
val = secure? mpi_debug_alloc_secure( nlimbs, info )
: mpi_debug_alloc( nlimbs, info );
#else
val = secure? mpi_alloc_secure( nlimbs )
: mpi_alloc( nlimbs );
#endif
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
val->nbits = nbits;
j= val->nlimbs = nlimbs;
val->sign = 0;
for( ; j > 0; j-- ) {
a = 0;
for(; i < BYTES_PER_MPI_LIMB; i++ ) {
if (nread == nmax) {
#ifdef M_DEBUG
mpi_debug_free (val);
#else
mpi_free (val);
#endif
val = NULL;
goto overflow;
}
a <<= 8;
a |= iobuf_get(inp) & 0xff; nread++;
}
i = 0;
val->d[j-1] = a;
}
leave:
*ret_nread = nread;
return val;
overflow:
log_error ("mpi larger than indicated length (%u bytes)\n", nmax);
*ret_nread = nread;
return val;
}
/*
* Generate a random secret exponent K less than Q.
* Note that ECDSA uses this code also to generate D.
*/
gcry_mpi_t
_gcry_dsa_gen_k (gcry_mpi_t q, int security_level)
{
gcry_mpi_t k = mpi_alloc_secure (mpi_get_nlimbs (q));
unsigned int nbits = mpi_get_nbits (q);
unsigned int nbytes = (nbits+7)/8;
char *rndbuf = NULL;
/* To learn why we don't use mpi_mod to get the requested bit size,
read the paper: "The Insecurity of the Digital Signature
Algorithm with Partially Known Nonces" by Nguyen and Shparlinski.
Journal of Cryptology, New York. Vol 15, nr 3 (2003) */
if (DBG_CIPHER)
log_debug ("choosing a random k of %u bits at seclevel %d\n",
nbits, security_level);
for (;;)
{
if ( !rndbuf || nbits < 32 )
{
xfree (rndbuf);
rndbuf = _gcry_random_bytes_secure (nbytes, security_level);
}
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 these extra bytes here.
However the required management code is more complex and
thus we better use this simple method. */
char *pp = _gcry_random_bytes_secure (4, security_level);
memcpy (rndbuf, pp, 4);
xfree (pp);
}
_gcry_mpi_set_buffer (k, rndbuf, nbytes, 0);
/* Make sure we have the requested number of bits. This code
looks a bit funny but it is easy to understand if you
consider that mpi_set_highbit clears all higher bits. We
don't have a clear_highbit, thus we first set the high bit
and then clear it again. */
if (mpi_test_bit (k, nbits-1))
mpi_set_highbit (k, nbits-1);
else
{
mpi_set_highbit (k, nbits-1);
mpi_clear_bit (k, nbits-1);
}
if (!(mpi_cmp (k, q) < 0)) /* check: k < q */
{
if (DBG_CIPHER)
log_debug ("\tk too large - again\n");
continue; /* no */
}
if (!(mpi_cmp_ui (k, 0) > 0)) /* check: k > 0 */
{
if (DBG_CIPHER)
log_debug ("\tk is zero - again\n");
continue; /* no */
}
break; /* okay */
}
xfree (rndbuf);
return k;
}