riot-ci/RIOT
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Merge pull request #15239 from benpicco/sys/luid-tweak

Browse Source 
sys/luid: improve luid_base() algorithm
This commit is contained in:
benpicco 2020-10-19 09:55:33 +02:00 committed by GitHub
commit fdc201a299
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 13 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
sys/luid/luid.c
View File

@ -26,8 +26,17 @@
#include "luid.h" #include "luid.h"
#ifndef MAX #if CPUID_LEN
#define MAX(a, b) (((a) > (b)) ? (a) : (b)) /* based on DJB2 Hash */
static void _luid_round(const uint8_t *in, size_t in_len, uint8_t *out, size_t out_len)
{
uint32_t hash = 5381;
for (size_t i = 0; i < in_len; i++) {
hash = hash * 33 + in[i];
out[i % out_len] ^= hash;
}
}
#endif #endif
void __attribute__((weak)) luid_base(void *buf, size_t len) void __attribute__((weak)) luid_base(void *buf, size_t len)
@ -35,34 +44,11 @@ void __attribute__((weak)) luid_base(void *buf, size_t len)
memset(buf, LUID_BACKUP_SEED, len); memset(buf, LUID_BACKUP_SEED, len);
#if CPUID_LEN #if CPUID_LEN
uint8_t *out = buf;
uint8_t cid[CPUID_LEN]; uint8_t cid[CPUID_LEN];
uint8_t sum = 0;
cpuid_get(cid); cpuid_get(cid);
/* CPU ID is XORed with LUID_BACKUP_SEED. _luid_round(cid, sizeof(cid), buf, len);
* Then Fisher–Yates shuffle is performed to mix _luid_round(buf, len, buf, len);
* the bytes, as often large continuous chunks of
* CPU ID are equal on machines with the same CPU.
*/
for (size_t i = 0; i < MAX(len, CPUID_LEN); i++) {
uint8_t tmp, j, k;
j = i % len;
k = i % CPUID_LEN;
/* xor with CPU ID */
out[j] ^= cid[k];
/* get 'random' position */
sum += out[j];
k = sum % (j + 1);
/* shuffle bytes */
tmp = out[j];
out[j] = out[k];
out[k] = tmp;
}
#endif #endif
} }