mirror of
https://gitlab.isc.org/isc-projects/bind9
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make the lfsr's real lfsr's, and use two of them to generate random-looking IDs
This commit is contained in:
Michael Graff
parent
0287710fe0
commit
b8ef99c3a7
@ -27,32 +27,23 @@ int
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main(int argc, char **argv)
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{
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isc_lfsr_t lfsr1, lfsr2;
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int i, j;
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int i;
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isc_uint32_t temp;
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UNUSED(argc);
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UNUSED(argv);
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printf("Known LFSRs:\n");
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i = 0;
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while (isc_lfsr_standard[i].bits != 0) {
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printf("%2d: %2d bits, %08x initial state, %08x tap\n",
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i, isc_lfsr_standard[i].bits,
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isc_lfsr_standard[i].state, isc_lfsr_standard[i].tap);
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i++;
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}
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/*
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* Verify that returned values are reproducable.
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*/
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lfsr1 = isc_lfsr_standard[3];
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isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
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for (i = 0 ; i < 32 ; i++) {
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state[i] = isc_lfsr_generate(&lfsr1);
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isc_lfsr_generate(&lfsr1, &state[i], 4);
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printf("lfsr1: state[%2d] = %08x\n", i, state[i]);
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}
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lfsr1 = isc_lfsr_standard[3];
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isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
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for (i = 0 ; i < 32 ; i++) {
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temp = isc_lfsr_generate(&lfsr1);
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isc_lfsr_generate(&lfsr1, &temp, 4);
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if (state[i] != temp)
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printf("lfsr1: state[%2d] = %08x, but new state is %08x\n",
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i, state[i], temp);
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@ -61,14 +52,16 @@ main(int argc, char **argv)
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/*
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* Now do the same with skipping.
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*/
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lfsr1 = isc_lfsr_standard[3];
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isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
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for (i = 0 ; i < 32 ; i++) {
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state[i] = isc_lfsr_skipgenerate(&lfsr1, 6);
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isc_lfsr_generate(&lfsr1, &state[i], 4);
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isc_lfsr_skip(&lfsr1, 32);
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printf("lfsr1: state[%2d] = %08x\n", i, state[i]);
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}
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lfsr1 = isc_lfsr_standard[3];
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isc_lfsr_init(&lfsr1, 0, 32, 0x80000057U, 0, NULL, NULL);
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for (i = 0 ; i < 32 ; i++) {
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temp = isc_lfsr_skipgenerate(&lfsr1, 6);
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isc_lfsr_generate(&lfsr1, &temp, 4);
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isc_lfsr_skip(&lfsr1, 32);
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if (state[i] != temp)
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printf("lfsr1: state[%2d] = %08x, but new state is %08x\n",
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i, state[i], temp);
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@ -76,22 +69,22 @@ main(int argc, char **argv)
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/*
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* Try to find the period of the LFSR.
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*
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* x^16 + x^5 + x^3 + x^2 + 1
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*/
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lfsr2 = isc_lfsr_standard[1];
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printf("Searching for repeating patterns in a %d-bit LFSR\n",
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lfsr2.bits);
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for (i = 0 ; i < (1024 * 64) ; i++)
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state[i] = isc_lfsr_generate(&lfsr2);
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for (i = 0 ; i < (1024 * 64) ; i++) {
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for (j = i + 1 ; j < (1024 * 64) ; j++) {
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if (state[i] == state[j]) {
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printf("%08x: state %d and %d are the same, distance %d.\n",
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state[i], i, j, j - i);
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goto next_i;
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}
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}
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next_i:
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isc_lfsr_init(&lfsr2, 0, 16, 0x00008016U, 0, NULL, NULL);
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for (i = 0 ; i < 32 ; i++) {
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isc_lfsr_generate(&lfsr2, &state[i], 4);
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printf("lfsr2: state[%2d] = %08x\n", i, state[i]);
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}
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isc_lfsr_init(&lfsr2, 0, 16, 0x00008016U, 0, NULL, NULL);
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for (i = 0 ; i < 32 ; i++) {
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isc_lfsr_generate(&lfsr2, &temp, 4);
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if (state[i] != temp)
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printf("lfsr2: state[%2d] = %08x, but new state is %08x\n",
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i, state[i], temp);
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}
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return (0);
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}
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@ -88,7 +88,8 @@ struct dns_dispatch {
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ISC_LIST(dns_dispentry_t) rq_handlers; /* request handler list */
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ISC_LIST(dns_dispatchevent_t) rq_events; /* holder for rq events */
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dns_tcpmsg_t tcpmsg; /* for tcp streams */
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isc_lfsr_t qid_lfsr; /* state generator info */
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isc_lfsr_t qid_lfsr1; /* state generator info */
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isc_lfsr_t qid_lfsr2; /* state generator info */
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unsigned int qid_nbuckets; /* hash table size */
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unsigned int qid_increment; /* id increment on collision */
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dns_displist_t *qid_table; /* the table itself */
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@ -125,6 +126,16 @@ static dns_dispentry_t *linear_first(dns_dispatch_t *disp);
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static dns_dispentry_t *linear_next(dns_dispatch_t *disp,
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dns_dispentry_t *resp);
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static void
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reseed_lfsr(isc_lfsr_t *lfsr, void *arg)
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{
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UNUSED(arg);
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lfsr->count = (random() & 0x1f) + 32; /* From 32 to 63 states */
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lfsr->state = random();
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}
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/*
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* Return an unpredictable message ID.
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*/
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@ -133,7 +144,7 @@ randomid(dns_dispatch_t *disp)
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{
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isc_uint32_t id;
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id = isc_lfsr_generate(&disp->qid_lfsr);
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id = isc_lfsr_generate32(&disp->qid_lfsr1, &disp->qid_lfsr2);
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return ((dns_messageid_t)(id & 0x0000ffff));
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}
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@ -887,10 +898,19 @@ dns_dispatch_create(isc_mem_t *mctx, isc_socket_t *sock, isc_task_t *task,
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}
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/*
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* Initialize to a 32-bit LFSR.
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* x^31 + x^6 + x^4 + x^2 + x + 1
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* Initialize to a 32-bit LFSR. Both of these are from Applied
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* Cryptography.
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*
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* lfsr1:
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* x^32 + x^7 + x^5 + x^3 + x^2 + x + 1
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*
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* lfsr2:
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* x^32 + x^7 + x^6 + x^2 + 1
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*/
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isc_lfsr_init(&disp->qid_lfsr, random(), 32, 0x80000057U);
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isc_lfsr_init(&disp->qid_lfsr1, 0, 32, 0x80000057U,
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0, reseed_lfsr, disp);
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isc_lfsr_init(&disp->qid_lfsr2, 0, 32, 0x800000c2U,
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0, reseed_lfsr, disp);
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disp->magic = DISPATCH_MAGIC;
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@ -20,22 +20,31 @@
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#include <isc/types.h>
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typedef struct isc_lfsr isc_lfsr_t;
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/*
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* This function is called when reseeding is needed. It is allowed to
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* modify any state in the LFSR in any way it sees fit OTHER THAN "bits".
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*
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* It MUST set "count" to a new value or the lfsr will never reseed again.
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*
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* Also, a reseed will never occur in the middle of an extraction. This
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* is purely an optimization, and is probably what one would want.
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*/
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typedef void (*isc_lfsrreseed_t)(isc_lfsr_t *, void *);
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/*
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* The members of this structure can be used by the application, but care
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* needs to be taken to not change state once the lfsr is in operation.
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*/
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typedef struct {
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isc_uint32_t state; /* previous state */
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unsigned int bits; /* length */
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isc_uint32_t tap; /* bit taps */
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} isc_lfsr_t;
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/*
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* This structure contains some standard LFSR values that can be used.
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* One can use the isc_lfsr_findlfsr() to search for one with at least
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* a certain number of bits.
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*/
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extern isc_lfsr_t isc_lfsr_standard[];
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struct isc_lfsr {
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isc_uint32_t state; /* previous state */
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unsigned int bits; /* length */
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isc_uint32_t tap; /* bit taps */
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unsigned int count; /* reseed count (in BITS!) */
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isc_lfsrreseed_t reseed; /* reseed function */
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void *arg; /* reseed function argument */
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};
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ISC_LANG_BEGINDECLS
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@ -45,24 +54,9 @@ ISC_LANG_BEGINDECLS
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* bit length 32 will have 2^32 unique states before repeating.
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*/
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isc_lfsr_t *isc_lfsr_findlfsr(unsigned int bits);
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/*
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* Find an LFSR that has at least "bits" of state.
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*
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* Requires:
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*
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* 8 <= bits <= 32
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*
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* Returns:
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*
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* NULL if no LFSR can be found.
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*
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* If NON-null, it points to the first LFSR in the standard LFSR table
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* that satisfies the requirements.
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*/
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void isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
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isc_uint32_t tap);
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isc_uint32_t tap, unsigned int count,
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isc_lfsrreseed_t reseed, void *arg);
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/*
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* Initialize an LFSR.
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*
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@ -80,28 +74,40 @@ void isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
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* tap != 0
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*/
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isc_uint32_t isc_lfsr_generate(isc_lfsr_t *lfsr);
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void isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count);
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/*
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* Return the next state in the LFSR.
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* Returns "count" bytes of data from the LFSR.
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*
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* Requires:
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*
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* lfsr be valid.
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*
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* data != NULL.
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*
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* count > 0.
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*/
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void isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip);
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/*
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* Skip "skip" states.
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*
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* Requires:
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*
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* lfsr be valid.
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*/
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isc_uint32_t isc_lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip);
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/*
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* Skip "skip" states, then return the next state after that.
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*
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* Requiremens are the same as for isc_lfsr_generate(), above.
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*/
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isc_uint32_t isc_lfsr_lfsrskipgenerate(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2,
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unsigned int skipbits);
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isc_uint32_t isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2);
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/*
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* Given two LFSRs, use the current state from each to skip entries in the
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* other. The next states are then xor'd together and returned.
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*
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* WARNING:
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*
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* This function is used only for very, very low security data, such
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* as DNS message IDs where it is desired to have an unpredictable
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* stream of bytes that are harder to predict than a simple flooding
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* attack.
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*
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* Notes:
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*
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* Since the current state from each of the LFSRs is used to skip
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124
lib/isc/lfsr.c
124
lib/isc/lfsr.c
@ -20,31 +20,12 @@
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#include <isc/assertions.h>
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#include <isc/lfsr.h>
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/*
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* Any LFSR added to this table needs to have a large period.
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* Entries should be added from longest bit state to smallest bit state.
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* XXXMLG Need to pull some from Applied Crypto.
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*/
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isc_lfsr_t isc_lfsr_standard[] = {
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{ 0, 32, 0x80000057U }, /* 32-bit, x^31 + x^6 + x^4 + x^2 + x + 1 */
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{ 0, 32, 0x80000047U }, /* 32-bit, x^31 + x^6 + x^2 + x + 1 */
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{ 0, 30, 0x20000029U }, /* 30-bit, x^29 + x^6 + x^3 + 1 */
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{ 0, 19, 0x00040013U }, /* 19-bit, x^18 + x^4 + x + 1 */
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{ 0, 13, 0x0000100dU }, /* 13-bit, x^12 + x^3 + x^2 + 1 */
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{ 0, 0, 0}
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};
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#define VALID_LFSR(x) (x != NULL)
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isc_lfsr_t *
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isc_lfsr_findlfsr(unsigned int bits)
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{
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return (NULL); /* XXXMLG implement? */
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}
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void
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isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
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isc_uint32_t tap)
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isc_uint32_t tap, unsigned int count,
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isc_lfsrreseed_t reseed, void *arg)
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{
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REQUIRE(VALID_LFSR(lfsr));
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REQUIRE(8 <= bits && bits <= 32);
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@ -53,6 +34,14 @@ isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
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lfsr->state = state;
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lfsr->bits = bits;
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lfsr->tap = tap;
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lfsr->count = count;
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lfsr->reseed = reseed;
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lfsr->arg = arg;
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if (count == 0 && reseed != NULL)
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reseed(lfsr, arg);
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if (lfsr->state == 0)
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lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
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}
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/*
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@ -61,31 +50,63 @@ isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
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static inline isc_uint32_t
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lfsr_generate(isc_lfsr_t *lfsr)
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{
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unsigned int nbits;
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unsigned int highbit;
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nbits = lfsr->bits - 1;
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highbit = 1 << (lfsr->bits - 1);
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/*
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* If the previous state is zero, we must fill it with something
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* here, or we will begin to generate an extremely predictable output.
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*
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* First, give the reseed function a crack at it. If the state is
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* still 0, set it to all ones.
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*/
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if (lfsr->state == 0)
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lfsr->state = (-1) & ((1 << nbits) - 1);
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if (lfsr->state == 0) {
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if (lfsr->reseed != NULL)
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lfsr->reseed(lfsr, lfsr->arg);
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if (lfsr->state == 0)
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lfsr->state = 0xffffffffU >> (32 - lfsr->bits);
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}
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if (lfsr->state & 1)
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lfsr->state = ((lfsr->state ^ lfsr->tap) >> 1) | (1 << nbits);
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else
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if (lfsr->state & 0x01) {
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lfsr->state = ((lfsr->state ^ lfsr->tap) >> 1) | highbit;
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return (1);
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} else {
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lfsr->state >>= 1;
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return (lfsr->state);
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return (0);
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}
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}
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isc_uint32_t
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isc_lfsr_generate(isc_lfsr_t *lfsr)
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void
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isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count)
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{
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REQUIRE(VALID_LFSR(lfsr));
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unsigned char *p;
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unsigned int bit;
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unsigned int byte;
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return (lfsr_generate(lfsr));
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REQUIRE(VALID_LFSR(lfsr));
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REQUIRE(data != NULL);
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REQUIRE(count > 0);
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p = data;
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byte = count;
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while (byte--) {
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*p = 0;
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for (bit = 0 ; bit < 7 ; bit++) {
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*p |= lfsr_generate(lfsr);
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*p <<= 1;
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}
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*p |= lfsr_generate(lfsr);
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p++;
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}
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if (lfsr->count != 0 && lfsr->reseed != NULL) {
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if (lfsr->count <= count * 8)
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lfsr->reseed(lfsr, lfsr->arg);
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else
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lfsr->count -= (count * 8);
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}
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}
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static inline isc_uint32_t
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@ -94,51 +115,38 @@ lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip)
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while (skip--)
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(void)lfsr_generate(lfsr);
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return (lfsr_generate(lfsr));
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(void)lfsr_generate(lfsr);
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return (lfsr->state);
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}
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/*
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* Skip "skip" states in "lfsr" and return the ending state.
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* Skip "skip" states in "lfsr".
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*/
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isc_uint32_t
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isc_lfsr_skipgenerate(isc_lfsr_t *lfsr, unsigned int skip)
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void
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isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip)
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{
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||||
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);
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user