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BN_rand_range() needs a BN_rand() variant that doesn't set the MSB.

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This commit is contained in:
Ulf Möller 2001-02-20 00:17:46 +00:00
parent 15ed15d3e4
commit faa624f9f9
2 changed files with 23 additions and 18 deletions
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27
crypto/bn/bn_rand.c
View file

@ -100,24 +100,27 @@ static int bnrand(int pseudorand, BIGNUM *rnd, int bits, int top, int bottom)
goto err;
}
if (top)
if (top != -1)
{
if (bit == 0)
if (top)
{
buf[0]=1;
buf[1]|=0x80;
if (bit == 0)
{
buf[0]=1;
buf[1]|=0x80;
}
else
{
buf[0]|=(3<<(bit-1));
buf[0]&= ~(mask<<1);
}
}
else
{
buf[0]|=(3<<(bit-1));
buf[0]|=(1<<bit);
buf[0]&= ~(mask<<1);
}
}
else
{
buf[0]|=(1<<bit);
buf[0]&= ~(mask<<1);
}
if (bottom) /* set bottom bits to whatever odd is */
buf[bytes-1]|=1;
if (!BN_bin2bn(buf,bytes,rnd)) goto err;
@ -163,7 +166,7 @@ int BN_rand_range(BIGNUM *r, BIGNUM *range)
do
{
/* range = 11..._2, so each iteration succeeds with probability >= .75 */
if (!BN_rand(r, n, 0, 0)) return 0;
if (!BN_rand(r, n, -1, 0)) return 0;
}
while (BN_cmp(r, range) >= 0);
}
@ -173,7 +176,7 @@ int BN_rand_range(BIGNUM *r, BIGNUM *range)
* so 3*range (= 11..._2) is exactly one bit longer than range */
do
{
if (!BN_rand(r, n + 1, 0, 0)) return 0;
if (!BN_rand(r, n + 1, -1, 0)) return 0;
/* If r < 3*range, use r := r MOD range
* (which is either r, r - range, or r - 2*range).
* Otherwise, iterate once more.

14
doc/crypto/BN_rand.pod
View file

@ -17,10 +17,12 @@ BN_rand, BN_pseudo_rand - generate pseudo-random number
=head1 DESCRIPTION
BN_rand() generates a cryptographically strong pseudo-random number of
B<bits> bits in length and stores it in B<rnd>. If B<top> is true, the
two most significant bits of the number will be set to 1, so that the
product of two such random numbers will always have 2*B<bits> length.
If B<bottom> is true, the number will be odd.
B<bits> bits in length and stores it in B<rnd>. If B<top> is -1, the
most significant bit of the random number can be zero. If B<top> is 0,
it is set to 1, and if B<top> is 1, the two most significant bits of
the number will be set to 1, so that the product of two such random
numbers will always have 2*B<bits> length. If B<bottom> is true, the
number will be odd.
BN_pseudo_rand() does the same, but pseudo-random numbers generated by
this function are not necessarily unpredictable. They can be used for
@ -45,7 +47,7 @@ L<RAND_add(3)|RAND_add(3)>, L<RAND_bytes(3)|RAND_bytes(3)>
=head1 HISTORY
BN_rand() is available in all versions of SSLeay and OpenSSL.
BN_pseudo_rand() was added in OpenSSL 0.9.5, and BN_rand_range()
in OpenSSL 0.9.6a.
BN_pseudo_rand() was added in OpenSSL 0.9.5. The B<top> == -1 case
and the function BN_rand_range() were added in OpenSSL 0.9.6a.
=cut