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add byte_equal_notimingattack

master
Felix von Leitner 9 years ago
parent
commit
c5a5c2d6bf
  1. 1
      CHANGES
  2. 2
      byte.h
  3. 19
      byte/byte_equal_notimingattack.c

1
CHANGES

@ -9,6 +9,7 @@
add io_fd_canwrite (like io_fd but assume the fd is writable)
save a few syscalls here and there
add awesome hack in isset.h (comex, Linus Torvalds)
add byte_equal_notimingattack
0.28:
add uint64 pack and unpack routines

2
byte.h

@ -41,6 +41,8 @@ void byte_zero(void* out, size_t len);
#define byte_equal(s,n,t) (!byte_diff((s),(n),(t)))
int byte_equal_notimingattack(const void* a, size_t len,const void* b) __pure__;
#ifdef __cplusplus
}
#endif

19
byte/byte_equal_notimingattack.c

@ -0,0 +1,19 @@
#include <byte.h>
/* If you need to compare a password or a hash value, the timing of the
* comparison function can give valuable clues to the attacker. Let's
* say the password is 123456 and the attacker tries abcdef. If the
* comparision function fails at the first byte without looking at the
* other bytes, then the attacker can measure the difference in runtime
* and deduce which byte was wrong, reducing the attack space from
* exponential to polynomial. */
int byte_equal_notimingattack(const void* a, size_t len,const void* b) {
size_t i;
const unsigned char* x=(const unsigned char*)a;
const unsigned char* y=(const unsigned char*)b;
unsigned char res=0;
for (i=0; i<len; ++i) {
res |= (x[i]^y[i]);
}
return res==0;
}
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