int mpi_cmp(MPI u, MPI v)
{
mpi_size_t usize, vsize;
int cmp;
mpi_normalize(u);
mpi_normalize(v);
usize = u->nlimbs;
vsize = v->nlimbs;
if (!u->sign && v->sign)
return 1;
if (u->sign && !v->sign)
return -1;
if (usize != vsize && !u->sign && !v->sign)
return usize - vsize;
if (usize != vsize && u->sign && v->sign)
return vsize + usize;
if (!usize)
return 0;
cmp = mpihelp_cmp(u->d, v->d, usize);
if (!cmp)
return 0;
if ((cmp < 0 ? 1 : 0) == (u->sign ? 1 : 0))
return 1;
return -1;
}
/* This function returns a new context for Barrett based operations on
the modulus M. This context needs to be released using
_gcry_mpi_barrett_free. If COPY is true M will be transferred to
the context and the user may change M. If COPY is false, M may not
be changed until gcry_mpi_barrett_free has been called. */
mpi_barrett_t
_gcry_mpi_barrett_init (gcry_mpi_t m, int copy)
{
mpi_barrett_t ctx;
gcry_mpi_t tmp;
mpi_normalize (m);
ctx = xcalloc (1, sizeof *ctx);
if (copy)
{
ctx->m = mpi_copy (m);
ctx->m_copied = 1;
}
else
ctx->m = m;
ctx->k = mpi_get_nlimbs (m);
tmp = mpi_alloc (ctx->k + 1);
/* Barrett precalculation: y = floor(b^(2k) / m). */
mpi_set_ui (tmp, 1);
mpi_lshift_limbs (tmp, 2 * ctx->k);
mpi_fdiv_q (tmp, tmp, m);
ctx->y = tmp;
ctx->r1 = mpi_alloc ( 2 * ctx->k + 1 );
ctx->r2 = mpi_alloc ( 2 * ctx->k + 1 );
return ctx;
}
/* R = X mod M
Using Barrett reduction. Before using this function
_gcry_mpi_barrett_init must have been called to do the
precalculations. CTX is the context created by this precalculation
and also conveys M. If the Barret reduction could no be done a
straightforward reduction method is used.
We assume that these conditions are met:
Input: x =(x_2k-1 ...x_0)_b
m =(m_k-1 ....m_0)_b with m_k-1 != 0
Output: r = x mod m
*/
void
_gcry_mpi_mod_barrett (gcry_mpi_t r, gcry_mpi_t x, mpi_barrett_t ctx)
{
gcry_mpi_t m = ctx->m;
int k = ctx->k;
gcry_mpi_t y = ctx->y;
gcry_mpi_t r1 = ctx->r1;
gcry_mpi_t r2 = ctx->r2;
int sign;
mpi_normalize (x);
if (mpi_get_nlimbs (x) > 2*k )
{
mpi_mod (r, x, m);
return;
}
sign = x->sign;
x->sign = 0;
/* 1. q1 = floor( x / b^k-1)
* q2 = q1 * y
* q3 = floor( q2 / b^k+1 )
* Actually, we don't need qx, we can work direct on r2
*/
mpi_set ( r2, x );
mpi_rshift_limbs ( r2, k-1 );
mpi_mul ( r2, r2, y );
mpi_rshift_limbs ( r2, k+1 );
/* 2. r1 = x mod b^k+1
* r2 = q3 * m mod b^k+1
* r = r1 - r2
* 3. if r < 0 then r = r + b^k+1
*/
mpi_set ( r1, x );
if ( r1->nlimbs > k+1 ) /* Quick modulo operation. */
r1->nlimbs = k+1;
mpi_mul ( r2, r2, m );
if ( r2->nlimbs > k+1 ) /* Quick modulo operation. */
r2->nlimbs = k+1;
mpi_sub ( r, r1, r2 );
if ( mpi_has_sign ( r ) )
{
if (!ctx->r3)
{
ctx->r3 = mpi_alloc ( k + 2 );
mpi_set_ui (ctx->r3, 1);
mpi_lshift_limbs (ctx->r3, k + 1 );
}
mpi_add ( r, r, ctx->r3 );
}
/* 4. while r >= m do r = r - m */
while ( mpi_cmp( r, m ) >= 0 )
mpi_sub ( r, r, m );
x->sign = sign;
}
static void
decrypt(MPI output, MPI a, MPI b, ELG_secret_key *skey )
{
MPI t1 = mpi_alloc_secure( mpi_get_nlimbs( skey->p ) );
mpi_normalize (a);
mpi_normalize (b);
/* output = b/(a^x) mod p */
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);
}
/****************
* Barrett precalculation: y = floor(b^(2k) / m)
*/
static gcry_mpi_t
init_barrett( gcry_mpi_t m, int *k, gcry_mpi_t *r1, gcry_mpi_t *r2 )
{
gcry_mpi_t tmp;
mpi_normalize( m );
*k = mpi_get_nlimbs( m );
tmp = mpi_alloc( *k + 1 );
mpi_set_ui( tmp, 1 );
mpi_lshift_limbs( tmp, 2 * *k );
mpi_fdiv_q( tmp, tmp, m );
*r1 = mpi_alloc( 2* *k + 1 );
*r2 = mpi_alloc( 2* *k + 1 );
return tmp;
}
/****************
* Barrett reduction: We assume that these conditions are met:
* Given x =(x_2k-1 ...x_0)_b
* m =(m_k-1 ....m_0)_b with m_k-1 != 0
* Output r = x mod m
* Before using this function init_barret must be used to calucalte y and k.
* Returns: false = no error
* true = can't perform barret reduction
*/
static int
calc_barrett( gcry_mpi_t r, gcry_mpi_t x, gcry_mpi_t m, gcry_mpi_t y, int k, gcry_mpi_t r1, gcry_mpi_t r2 )
{
int xx = k > 3 ? k-3:0;
mpi_normalize( x );
if( mpi_get_nlimbs(x) > 2*k )
return 1; /* can't do it */
/* 1. q1 = floor( x / b^k-1)
* q2 = q1 * y
* q3 = floor( q2 / b^k+1 )
* Actually, we don't need qx, we can work direct on r2
*/
mpi_set( r2, x );
mpi_rshift_limbs( r2, k-1 );
mpi_mul( r2, r2, y );
mpi_rshift_limbs( r2, k+1 );
/* 2. r1 = x mod b^k+1
* r2 = q3 * m mod b^k+1
* r = r1 - r2
* 3. if r < 0 then r = r + b^k+1
*/
mpi_set( r1, x );
if( r1->nlimbs > k+1 ) /* quick modulo operation */
r1->nlimbs = k+1;
mpi_mul( r2, r2, m );
if( r2->nlimbs > k+1 ) /* quick modulo operation */
r2->nlimbs = k+1;
mpi_sub( r, r1, r2 );
if( mpi_has_sign (r) ) {
gcry_mpi_t tmp;
tmp = mpi_alloc( k + 2 );
mpi_set_ui( tmp, 1 );
mpi_lshift_limbs( tmp, k+1 );
mpi_add( r, r, tmp );
mpi_free(tmp);
}
/* 4. while r >= m do r = r - m */
while( mpi_cmp( r, m ) >= 0 )
mpi_sub( r, r, m );
return 0;
}
/****************
* Return the number of bits in A.
*/
unsigned
mpi_get_nbits( MPI a )
{
unsigned n;
mpi_normalize( a );
if( a->nlimbs ) {
mpi_limb_t alimb = a->d[a->nlimbs-1];
if( alimb )
count_leading_zeros( n, alimb );
else
n = BITS_PER_MPI_LIMB;
n = BITS_PER_MPI_LIMB - n + (a->nlimbs-1) * BITS_PER_MPI_LIMB;
}
else
n = 0;
return n;
}
int mpi_cmp_ui(MPI u, unsigned long v)
{
mpi_limb_t limb = v;
mpi_normalize(u);
if (!u->nlimbs && !limb)
return 0;
if (u->sign)
return -1;
if (u->nlimbs > 1)
return 1;
if (u->d[0] == limb)
return 0;
else if (u->d[0] > limb)
return 1;
else
return -1;
}
/* 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);
}
