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Bugfixes to fp_prime_random_ex #4

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Bugfixes to fp_prime_random_ex #4

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08b3654
Avoid always generating 0x80 as MSB in primes.
rasky Sep 21, 2011
279da69
Remove usage of malloc() from fp_prime_random_ex.
rasky Sep 21, 2011
3bab60e
Remove unused parameter 't'
rasky Sep 26, 2011
d1dee8c
Fix a sign-extension bug on 64-bit platforms
rasky Sep 26, 2011
3d5ada6
Avoid writing directly into fp_digits through char*.
rasky Sep 26, 2011
faf0f96
Fix a bug in case the most significants bits were generated as zero.
rasky Sep 26, 2011
4c776ac
Simpify mask formula.
rasky Sep 27, 2011
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26 changes: 14 additions & 12 deletions src/headers/tfm.h
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Original file line number Diff line number Diff line change
@@ -1,10 +1,10 @@
/* TomsFastMath, a fast ISO C bignum library.
*
*
* This project is meant to fill in where LibTomMath
* falls short. That is speed ;-)
*
* This project is public domain and free for all purposes.
*
*
* Tom St Denis, [email protected]
*/
#ifndef TFM_H_
Expand All @@ -27,13 +27,13 @@
/* externally define this symbol to ignore the default settings, useful for changing the build from the make process */
#ifndef TFM_ALREADY_SET

/* do we want the large set of small multiplications ?
/* do we want the large set of small multiplications ?
Enable these if you are going to be doing a lot of small (<= 16 digit) multiplications say in ECC
Or if you're on a 64-bit machine doing RSA as a 1024-bit integer == 16 digits ;-)
*/
#define TFM_SMALL_SET

/* do we want huge code
/* do we want huge code
Enable these if you are doing 20, 24, 28, 32, 48, 64 digit multiplications (useful for RSA)
Less important on 64-bit machines as 32 digits == 2048 bits
*/
Expand Down Expand Up @@ -81,7 +81,7 @@
/* #define TFM_PRESCOTT */

/* Do we want timing resistant fp_exptmod() ?
* This makes it slower but also timing invariant with respect to the exponent
* This makes it slower but also timing invariant with respect to the exponent
*/
/* #define TFM_TIMING_RESISTANT */

Expand All @@ -106,7 +106,7 @@

/* autodetect x86-64 and make sure we are using 64-bit digits with x86-64 asm */
#if defined(__x86_64__)
#if defined(TFM_X86) || defined(TFM_SSE2) || defined(TFM_ARM)
#if defined(TFM_X86) || defined(TFM_SSE2) || defined(TFM_ARM)
#error x86-64 detected, x86-32/SSE2/ARM optimizations are not valid!
#endif
#if !defined(TFM_X86_64) && !defined(TFM_NO_ASM)
Expand All @@ -121,7 +121,7 @@

/* try to detect x86-32 */
#if defined(__i386__) && !defined(TFM_SSE2)
#if defined(TFM_X86_64) || defined(TFM_ARM)
#if defined(TFM_X86_64) || defined(TFM_ARM)
#error x86-32 detected, x86-64/ARM optimizations are not valid!
#endif
#if !defined(TFM_X86) && !defined(TFM_NO_ASM)
Expand Down Expand Up @@ -185,7 +185,7 @@
#undef TFM_PPC32
#undef TFM_PPC64
#undef TFM_AVR32
#undef TFM_ASM
#undef TFM_ASM
#endif

/* ECC helpers */
Expand Down Expand Up @@ -249,10 +249,11 @@
#endif
typedef ulong64 fp_digit;
typedef unsigned long fp_word __attribute__ ((mode(TI)));
#define DIGIT_SHIFT 6
#else
/* this is to make porting into LibTomCrypt easier :-) */
#ifndef CRYPT
#if defined(_MSC_VER) || defined(__BORLANDC__)
#if defined(_MSC_VER) || defined(__BORLANDC__)
typedef unsigned __int64 ulong64;
typedef signed __int64 long64;
#else
Expand All @@ -262,6 +263,7 @@
#endif
typedef unsigned long fp_digit;
typedef ulong64 fp_word;
#define DIGIT_SHIFT 5
#endif

/* # of digits this is */
Expand Down Expand Up @@ -290,7 +292,7 @@
/* a FP type */
typedef struct {
fp_digit dp[FP_SIZE];
int used,
int used,
sign;
} fp_int;

Expand Down Expand Up @@ -434,9 +436,9 @@ int fp_isprime(fp_int *a);
/* callback for fp_prime_random, should fill dst with random bytes and return how many read [upto len] */
typedef int tfm_prime_callback(unsigned char *dst, int len, void *dat);

#define fp_prime_random(a, t, size, bbs, cb, dat) fp_prime_random_ex(a, t, ((size) * 8) + 1, (bbs==1)?TFM_PRIME_BBS:0, cb, dat)
#define fp_prime_random(a, size, bbs, cb, dat) fp_prime_random_ex(a, ((size) * 8) + 1, (bbs==1)?TFM_PRIME_BBS:0, cb, dat)

int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback cb, void *dat);
int fp_prime_random_ex(fp_int *a, int size, int flags, tfm_prime_callback cb, void *dat);

/* radix conersions */
int fp_count_bits(fp_int *a);
Expand Down
83 changes: 41 additions & 42 deletions src/numtheory/fp_prime_random_ex.c
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,22 +1,29 @@
/* TomsFastMath, a fast ISO C bignum library.
*
*
* This project is meant to fill in where LibTomMath
* falls short. That is speed ;-)
*
* This project is public domain and free for all purposes.
*
*
* Tom St Denis, [email protected]
*/
#include <tfm.h>

#define fp_on_bitnum(a, bitnum) \
a->dp[(bitnum) >> DIGIT_SHIFT] |= (fp_digit)1 << ((bitnum) & (DIGIT_BIT-1))

#define fp_off_bitnum(a, bitnum) \
a->dp[(bitnum) >> DIGIT_SHIFT] &= ~((fp_digit)1 << ((bitnum) & (DIGIT_BIT-1)))

/* This is possibly the mother of all prime generation functions, muahahahahaha! */
int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback cb, void *dat)
int fp_prime_random_ex(fp_int *a, int size, int flags, tfm_prime_callback cb, void *dat)
{
unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb;
int res, err, bsize, maskOR_msb_offset;
fp_digit maskAND_msb, maskOR_lsb;
int res, bsize, dsize;
unsigned char buf[FP_SIZE * sizeof(fp_digit)];

/* sanity check the input */
if (size <= 1 || t <= 0) {
if (size <= 1) {
return FP_VAL;
}

Expand All @@ -25,26 +32,12 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback
flags |= TFM_PRIME_BBS;
}

/* calc the byte size */
bsize = (size>>3)+(size&7?1:0);
/* calc the digit size */
dsize = (size + DIGIT_BIT - 1) >> DIGIT_SHIFT;
bsize = (size + 7) >> 3;

/* we need a buffer of bsize bytes */
tmp = malloc(bsize);
if (tmp == NULL) {
return FP_MEM;
}

/* calc the maskAND value for the MSbyte*/
maskAND = 0xFF >> (8 - (size & 7));

/* calc the maskOR_msb */
maskOR_msb = 0;
maskOR_msb_offset = (size - 2) >> 3;
if (flags & TFM_PRIME_2MSB_ON) {
maskOR_msb |= 1 << ((size - 2) & 7);
} else if (flags & TFM_PRIME_2MSB_OFF) {
maskAND &= ~(1 << ((size - 2) & 7));
}
/* calc the maskAND value for the MSbyte */
maskAND_msb = FP_MASK >> ((DIGIT_BIT - size) & (DIGIT_BIT-1));

/* get the maskOR_lsb */
maskOR_lsb = 1;
Expand All @@ -54,21 +47,30 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback

do {
/* read the bytes */
if (cb(tmp, bsize, dat) != bsize) {
err = FP_VAL;
goto error;
if (cb(buf, bsize, dat) != bsize) {
return FP_VAL;
}

/* work over the MSbyte */
tmp[0] &= maskAND;
tmp[0] |= 1 << ((size - 1) & 7);
fp_read_unsigned_bin(a, buf, bsize);

/* make sure the MSbyte has the required number of bits */
a->dp[dsize-1] &= maskAND_msb;

/* Force a->used as well, it could be smaller if the highest bits were
generated as 0 by the callback. */
a->used = dsize;

/* mix in the maskORs */
tmp[maskOR_msb_offset] |= maskOR_msb;
tmp[bsize-1] |= maskOR_lsb;
/* modify the LSbyte as requested */
a->dp[0] |= maskOR_lsb;

/* read it in */
fp_read_unsigned_bin(a, tmp, bsize);
/* turn on the MSbit to force the requested magnitude */
fp_on_bitnum(a, size-1);

/* modify the 2nd MSBit */
if (flags & TFM_PRIME_2MSB_ON) {
fp_on_bitnum(a, size-2);
} else if (flags & TFM_PRIME_2MSB_OFF) {
fp_off_bitnum(a, size-2);
}

/* is it prime? */
res = fp_isprime(a);
Expand All @@ -78,7 +80,7 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback
/* see if (a-1)/2 is prime */
fp_sub_d(a, 1, a);
fp_div_2(a, a);

/* is it prime? */
res = fp_isprime(a);
}
Expand All @@ -90,10 +92,7 @@ int fp_prime_random_ex(fp_int *a, int t, int size, int flags, tfm_prime_callback
fp_add_d(a, 1, a);
}

err = FP_OKAY;
error:
free(tmp);
return err;
return FP_OKAY;
}

/* $Source$ */
Expand Down