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Use php_random_bytes() for uniqid() #2123

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Use php_random_bytes() for uniqid() #2123

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19 changes: 13 additions & 6 deletions ext/standard/uniqid.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,24 +35,26 @@
#include <sys/time.h>
#endif

#include "php_lcg.h"
#include "php_random.h"
#include "uniqid.h"

#define UNIQID_RAND_CHARS 10

static char convtab[] = "0123456789abcdefghijklmnopqrstuv";

/* {{{ proto string uniqid([string prefix [, bool more_entropy]])
Generates a unique ID */
#ifdef HAVE_GETTIMEOFDAY
PHP_FUNCTION(uniqid)
{
char *prefix = "";
#if defined(__CYGWIN__)
zend_bool more_entropy = 1;
#else
zend_bool more_entropy = 0;
#endif
zend_string *uniqid;
int sec, usec;
size_t prefix_len = 0;
struct timeval tv;
char bytes[UNIQID_RAND_CHARS*2];
int i, mask = (1 << 5) - 1;

if (zend_parse_parameters(ZEND_NUM_ARGS(), "|sb", &prefix, &prefix_len,
&more_entropy)) {
Expand All @@ -72,12 +74,17 @@ PHP_FUNCTION(uniqid)
gettimeofday((struct timeval *) &tv, (struct timezone *) NULL);
sec = (int) tv.tv_sec;
usec = (int) (tv.tv_usec % 0x100000);
php_random_bytes(bytes, UNIQID_RAND_CHARS*2, 1);
for (i = 0; i < UNIQID_RAND_CHARS; i++) {
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@CarwynNelson CarwynNelson Sep 21, 2016 •
edited
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I'm by no means knowledgeable on security (in fact I know almost nothing about it). But doesn't building up the uniqid like this (assuming that's what it's doing) open up a user to timing attacks?

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EDIT: In other words shouldn't building up of the uniqid be done in constant time?

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@yohgaki yohgaki Sep 22, 2016 •
edited
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@CarwynNelson
uniqid() produces timestamp based unique ID. This is what it supposed to do. (AFAIK, it was made for SMTP's message ID which uses timestamp based ID)
"more entropy" option should do better job. This RFC improves "more entropy" option by replacing php_combined_lcg() to php_random_bytes().

bytes[i] = convtab[bytes[i] & mask];
}
bytes[UNIQID_RAND_CHARS] = '\0';

/* The max value usec can have is 0xF423F, so we use only five hex
* digits for usecs.
*/
if (more_entropy) {
uniqid = strpprintf(0, "%s%08x%05x%.8F", prefix, sec, usec, php_combined_lcg() * 10);
uniqid = strpprintf(0, "%s%08x%05x%s", prefix, sec, usec, bytes);
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I can already see half the world breaking here...

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@yohgaki yohgaki Sep 10, 2016 •
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@Ocramius
Why? It could break code, but almost all code does not care return value from uniqid() at all.
e.g. https://searchcode.com/?q=uniqid&loc=0&loc2=10000&lan=24

} else {
uniqid = strpprintf(0, "%s%08x%05x", prefix, sec, usec);
}
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