mir/bind
2
0
Fork 0
mirror of https://gitlab.isc.org/isc-projects/bind9 synced 2025-08-29 21:47:59 +00:00
Code Issues Releases Wiki Activity

make the lfsr's real lfsr's, and use two of them to generate random-looking IDs

Browse Source
This commit is contained in:
Michael Graff 1999-12-16 00:07:21 +00:00
parent 0287710fe0
commit b8ef99c3a7
4 changed files with 162 additions and 135 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
bin/tests/lfsr_test.c
View File

@ -27,32 +27,23 @@ int
main(int argc, char **argv)
{
isc_lfsr_t lfsr1, lfsr2;
int i, j;
int i;
isc_uint32_t temp;
UNUSED(argc);
UNUSED(argv);
printf("Known LFSRs:\n");
i = 0;
while (isc_lfsr_standard[i].bits != 0) {
printf("%2d: %2d bits, %08x initial state, %08x tap\n",
i, isc_lfsr_standard[i].bits,
isc_lfsr_standard[i].state, isc_lfsr_standard[i].tap);
i++;
}
/*
* Verify that returned values are reproducable.
*/
lfsr1 = isc_lfsr_standard[3];
isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
for (i = 0 ; i < 32 ; i++) {
state[i] = isc_lfsr_generate(&lfsr1);
isc_lfsr_generate(&lfsr1, &state[i], 4);
printf("lfsr1: state[%2d] = %08x\n", i, state[i]);
}
lfsr1 = isc_lfsr_standard[3];
isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
for (i = 0 ; i < 32 ; i++) {
temp = isc_lfsr_generate(&lfsr1);
isc_lfsr_generate(&lfsr1, &temp, 4);
if (state[i] != temp)
printf("lfsr1: state[%2d] = %08x, but new state is %08x\n",
i, state[i], temp);
@ -61,14 +52,16 @@ main(int argc, char **argv)
/*
* Now do the same with skipping.
*/
lfsr1 = isc_lfsr_standard[3];
isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
for (i = 0 ; i < 32 ; i++) {
state[i] = isc_lfsr_skipgenerate(&lfsr1, 6);
isc_lfsr_generate(&lfsr1, &state[i], 4);
isc_lfsr_skip(&lfsr1, 32);
printf("lfsr1: state[%2d] = %08x\n", i, state[i]);
}
lfsr1 = isc_lfsr_standard[3];
isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
for (i = 0 ; i < 32 ; i++) {
temp = isc_lfsr_skipgenerate(&lfsr1, 6);
isc_lfsr_generate(&lfsr1, &temp, 4);
isc_lfsr_skip(&lfsr1, 32);
if (state[i] != temp)
printf("lfsr1: state[%2d] = %08x, but new state is %08x\n",
i, state[i], temp);
@ -76,22 +69,22 @@ main(int argc, char **argv)
/*
* Try to find the period of the LFSR.
*
* x^16 + x^5 + x^3 + x^2 + 1
*/
lfsr2 = isc_lfsr_standard[1];
printf("Searching for repeating patterns in a %d-bit LFSR\n",
lfsr2.bits);
for (i = 0 ; i < (1024 * 64) ; i++)
state[i] = isc_lfsr_generate(&lfsr2);
for (i = 0 ; i < (1024 * 64) ; i++) {
for (j = i + 1 ; j < (1024 * 64) ; j++) {
if (state[i] == state[j]) {
printf("%08x: state %d and %d are the same, distance %d.\n",
state[i], i, j, j - i);
goto next_i;
}
}
next_i:
isc_lfsr_init(&lfsr2, 0, 16, 0x00008016U, 0, NULL, NULL);
for (i = 0 ; i < 32 ; i++) {
isc_lfsr_generate(&lfsr2, &state[i], 4);
printf("lfsr2: state[%2d] = %08x\n", i, state[i]);
}
isc_lfsr_init(&lfsr2, 0, 16, 0x00008016U, 0, NULL, NULL);
for (i = 0 ; i < 32 ; i++) {
isc_lfsr_generate(&lfsr2, &temp, 4);
if (state[i] != temp)
printf("lfsr2: state[%2d] = %08x, but new state is %08x\n",
i, state[i], temp);
}
return (0);
}

30
lib/dns/dispatch.c
View File

@ -88,7 +88,8 @@ struct dns_dispatch {
ISC_LIST(dns_dispentry_t) rq_handlers; /* request handler list */
ISC_LIST(dns_dispatchevent_t) rq_events; /* holder for rq events */
dns_tcpmsg_t tcpmsg; /* for tcp streams */
isc_lfsr_t qid_lfsr; /* state generator info */
isc_lfsr_t qid_lfsr1; /* state generator info */
isc_lfsr_t qid_lfsr2; /* state generator info */
unsigned int qid_nbuckets; /* hash table size */
unsigned int qid_increment; /* id increment on collision */
dns_displist_t *qid_table; /* the table itself */
@ -125,6 +126,16 @@ static dns_dispentry_t *linear_first(dns_dispatch_t *disp);
static dns_dispentry_t *linear_next(dns_dispatch_t *disp,
dns_dispentry_t *resp);
static void
reseed_lfsr(isc_lfsr_t *lfsr, void *arg)
{
UNUSED(arg);
lfsr->count = (random() & 0x1f) + 32; /* From 32 to 63 states */
lfsr->state = random();
}
/*
* Return an unpredictable message ID.
*/
@ -133,7 +144,7 @@ randomid(dns_dispatch_t *disp)
{
isc_uint32_t id;
id = isc_lfsr_generate(&disp->qid_lfsr);
id = isc_lfsr_generate32(&disp->qid_lfsr1, &disp->qid_lfsr2);
return ((dns_messageid_t)(id & 0x0000ffff));
}
@ -887,10 +898,19 @@ dns_dispatch_create(isc_mem_t *mctx, isc_socket_t *sock, isc_task_t *task,
}
/*
* Initialize to a 32-bit LFSR.
* x^31 + x^6 + x^4 + x^2 + x + 1
* Initialize to a 32-bit LFSR. Both of these are from Applied
* Cryptography.
*
* lfsr1:
* x^32 + x^7 + x^5 + x^3 + x^2 + x + 1
*
* lfsr2:
* x^32 + x^7 + x^6 + x^2 + 1
*/
isc_lfsr_init(&disp->qid_lfsr, random(), 32, 0x80000057U);
isc_lfsr_init(&disp->qid_lfsr1, 0, 32, 0x80000057U,
0, reseed_lfsr, disp);
isc_lfsr_init(&disp->qid_lfsr2, 0, 32, 0x800000c2U,
0, reseed_lfsr, disp);
disp->magic = DISPATCH_MAGIC;

86
lib/isc/include/isc/lfsr.h
View File

@ -20,22 +20,31 @@
#include <isc/types.h>
typedef struct isc_lfsr isc_lfsr_t;
/*
* This function is called when reseeding is needed. It is allowed to
* modify any state in the LFSR in any way it sees fit OTHER THAN "bits".
*
* It MUST set "count" to a new value or the lfsr will never reseed again.
*
* Also, a reseed will never occur in the middle of an extraction. This
* is purely an optimization, and is probably what one would want.
*/
typedef void (*isc_lfsrreseed_t)(isc_lfsr_t *, void *);
/*
* The members of this structure can be used by the application, but care
* needs to be taken to not change state once the lfsr is in operation.
*/
typedef struct {
isc_uint32_t state; /* previous state */
unsigned int bits; /* length */
isc_uint32_t tap; /* bit taps */
} isc_lfsr_t;
/*
* This structure contains some standard LFSR values that can be used.
* One can use the isc_lfsr_findlfsr() to search for one with at least
* a certain number of bits.
*/
extern isc_lfsr_t isc_lfsr_standard[];
struct isc_lfsr {
isc_uint32_t state; /* previous state */
unsigned int bits; /* length */
isc_uint32_t tap; /* bit taps */
unsigned int count; /* reseed count (in BITS!) */
isc_lfsrreseed_t reseed; /* reseed function */
void *arg; /* reseed function argument */
};
ISC_LANG_BEGINDECLS
@ -45,24 +54,9 @@ ISC_LANG_BEGINDECLS
* bit length 32 will have 2^32 unique states before repeating.
*/
isc_lfsr_t *isc_lfsr_findlfsr(unsigned int bits);
/*
* Find an LFSR that has at least "bits" of state.
*
* Requires:
*
* 8 <= bits <= 32
*
* Returns:
*
* NULL if no LFSR can be found.
*
* If NON-null, it points to the first LFSR in the standard LFSR table
* that satisfies the requirements.
*/
void isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
isc_uint32_t tap);
isc_uint32_t tap, unsigned int count,
isc_lfsrreseed_t reseed, void *arg);
/*
* Initialize an LFSR.
*
@ -80,28 +74,40 @@ void isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
* tap != 0
*/
isc_uint32_t isc_lfsr_generate(isc_lfsr_t *lfsr);
void isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count);
/*
* Return the next state in the LFSR.
* Returns "count" bytes of data from the LFSR.
*
* Requires:
*
* lfsr be valid.
*
* data != NULL.
*
* count > 0.
*/
void isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip);
/*
* Skip "skip" states.
*
* Requires:
*
* lfsr be valid.
*/
isc_uint32_t isc_lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip);
/*
* Skip "skip" states, then return the next state after that.
*
* Requiremens are the same as for isc_lfsr_generate(), above.
*/
isc_uint32_t isc_lfsr_lfsrskipgenerate(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2,
unsigned int skipbits);
isc_uint32_t isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2);
/*
* Given two LFSRs, use the current state from each to skip entries in the
* other. The next states are then xor'd together and returned.
*
* WARNING:
*
* This function is used only for very, very low security data, such
* as DNS message IDs where it is desired to have an unpredictable
* stream of bytes that are harder to predict than a simple flooding
* attack.
*
* Notes:
*
* Since the current state from each of the LFSRs is used to skip

124
lib/isc/lfsr.c
View File

@ -20,31 +20,12 @@
#include <isc/assertions.h>
#include <isc/lfsr.h>
/*
* Any LFSR added to this table needs to have a large period.
* Entries should be added from longest bit state to smallest bit state.
* XXXMLG Need to pull some from Applied Crypto.
*/
isc_lfsr_t isc_lfsr_standard[] = {
{ 0, 32, 0x80000057U }, /* 32-bit, x^31 + x^6 + x^4 + x^2 + x + 1 */
{ 0, 32, 0x80000047U }, /* 32-bit, x^31 + x^6 + x^2 + x + 1 */
{ 0, 30, 0x20000029U }, /* 30-bit, x^29 + x^6 + x^3 + 1 */
{ 0, 19, 0x00040013U }, /* 19-bit, x^18 + x^4 + x + 1 */
{ 0, 13, 0x0000100dU }, /* 13-bit, x^12 + x^3 + x^2 + 1 */
{ 0, 0, 0}
};
#define VALID_LFSR(x) (x != NULL)
isc_lfsr_t *
isc_lfsr_findlfsr(unsigned int bits)
{
return (NULL); /* XXXMLG implement? */
}
void
isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
isc_uint32_t tap)
isc_uint32_t tap, unsigned int count,
isc_lfsrreseed_t reseed, void *arg)
{
REQUIRE(VALID_LFSR(lfsr));
REQUIRE(8 <= bits && bits <= 32);
@ -53,6 +34,14 @@ isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
lfsr->state = state;
lfsr->bits = bits;
lfsr->tap = tap;
lfsr->count = count;
lfsr->reseed = reseed;
lfsr->arg = arg;
if (count == 0 && reseed != NULL)
reseed(lfsr, arg);
if (lfsr->state == 0)
lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
}
/*
@ -61,31 +50,63 @@ isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
static inline isc_uint32_t
lfsr_generate(isc_lfsr_t *lfsr)
{
unsigned int nbits;
unsigned int highbit;
nbits = lfsr->bits - 1;
highbit = 1 << (lfsr->bits - 1);
/*
* If the previous state is zero, we must fill it with something
* here, or we will begin to generate an extremely predictable output.
*
* First, give the reseed function a crack at it. If the state is
* still 0, set it to all ones.
*/
if (lfsr->state == 0)
lfsr->state = (-1) & ((1 << nbits) - 1);
if (lfsr->state == 0) {
if (lfsr->reseed != NULL)
lfsr->reseed(lfsr, lfsr->arg);
if (lfsr->state == 0)
lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
}
if (lfsr->state & 1)
lfsr->state = ((lfsr->state ^ lfsr->tap) >> 1) | (1 << nbits);
else
if (lfsr->state & 0x01) {
lfsr->state = ((lfsr->state ^ lfsr->tap) >> 1) | highbit;
return (1);
} else {
lfsr->state >>= 1;
return (lfsr->state);
return (0);
}
}
isc_uint32_t
isc_lfsr_generate(isc_lfsr_t *lfsr)
void
isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count)
{
REQUIRE(VALID_LFSR(lfsr));
unsigned char *p;
unsigned int bit;
unsigned int byte;
return (lfsr_generate(lfsr));
REQUIRE(VALID_LFSR(lfsr));
REQUIRE(data != NULL);
REQUIRE(count > 0);
p = data;
byte = count;
while (byte--) {
*p = 0;
for (bit = 0 ; bit < 7 ; bit++) {
*p |= lfsr_generate(lfsr);
*p <<= 1;
}
*p |= lfsr_generate(lfsr);
p++;
}
if (lfsr->count != 0 && lfsr->reseed != NULL) {
if (lfsr->count <= count * 8)
lfsr->reseed(lfsr, lfsr->arg);
else
lfsr->count -= (count * 8);
}
}
static inline isc_uint32_t
@ -94,51 +115,38 @@ lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip)
while (skip--)
(void)lfsr_generate(lfsr);
return (lfsr_generate(lfsr));
(void)lfsr_generate(lfsr);
return (lfsr->state);
}
/*
* Skip "skip" states in "lfsr" and return the ending state.
* Skip "skip" states in "lfsr".
*/
isc_uint32_t
isc_lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip)
void
isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip)
{
REQUIRE(VALID_LFSR(lfsr));
return (lfsr_skipgenerate(lfsr, skip));
while (skip--)
(void)lfsr_generate(lfsr);
}
/*
* Skip states in lfsr1 and lfsr2 using the other's current state.
* Return the final state of lfsr1 ^ lfsr2.
*
* Since this uses the _previous_ state of the lfsrs, the the actual values
* they contain should never be released to anyone other than by return from
* this function.
*
* "skipbits" indicates how many lower bits should be used to advance the
* lfsrs. A good value is 1. If simple combining is desired (without
* skipping any values) one can use 0.
*/
isc_uint32_t
isc_lfsr_lfsrskipgenerate(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2,
unsigned int skipbits)
isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2)
{
isc_uint32_t state1, state2;
isc_uint32_t skip1, skip2;
isc_uint32_t skipmask;
REQUIRE(VALID_LFSR(lfsr1));
REQUIRE(VALID_LFSR(lfsr2));
REQUIRE(skipbits < 31);
if (skipbits == 0)
skipmask = 0;
else
skipmask = (1 << skipbits) - 1;
skip1 = lfsr1->state & skipmask;
skip2 = lfsr2->state & skipmask;
skip1 = lfsr1->state & 0x01;
skip2 = lfsr2->state & 0x01;
/* cross-skip. */
state1 = lfsr_skipgenerate(lfsr1, skip2);