CRYPTO_VERIFY16(3MONOCYPHER) | 3MONOCYPHER | CRYPTO_VERIFY16(3MONOCYPHER) |
crypto_verify16
,
crypto_verify32
,
crypto_verify64
—
#include <monocypher.h>
int
crypto_verify16
(const uint8_t
a[16], const uint8_t b[16]);
int
crypto_verify32
(const uint8_t
a[32], const uint8_t b[32]);
int
crypto_verify64
(const uint8_t
a[64], const uint8_t b[64]);
memcmp
() tend to exit when they find the first
difference, leaking information through timing differences.
As an example, say a message authentication code (MAC) is sent over the network along with a message, but the correct MAC is secret. If the attacker attempts a forgery, one does not want to reveal “your MAC is wrong, and it took 384 microseconds to tell”. If the next attempt takes 462 microseconds instead, it tells the attacker that they just guessed a byte correctly. That way, an attacker can derive the correct MAC byte by byte and successfully forge a message. This has led to practical attacks in the past.
To avoid such catastrophic failure,
crypto_verify16
(),
crypto_verify32
(), and
crypto_verify64
() provide comparison functions whose
timing is independent from the content of their input. They compare the
first 16, 32, or 64 bytes of the two byte arrays a and
b.
When in doubt, prefer these functions over
memcmp
().
crypto_verify16
(),
crypto_verify32
(),
crypto_verify64
(), functions first appeared in
Monocypher 1.1.0. They replaced the crypto_memcmp
()
and crypto_zerocmp
() functions that were present until
Monocypher 1.0.1.
March 31, 2020 | Debian |