nqcteq(3)

NAME

nqcteq — compare two buffers in constant time

LIBRARY

libnoqtis, -lnoqtis

SYNOPSIS

#include <noqtis.h>

int
nqcteq(const void *a, const void *b, size_t len);

DESCRIPTION

nqcteq() compares the len bytes at a and b in time that depends only on len, not on their contents or on where they first differ. Use it for MAC tags, shared secrets and anything else an attacker must not learn byte by byte; use memcmp(3) only for public data.

It does not order the buffers: it tells only whether they are equal.

RETURN VALUES

1 when the buffers are equal, 0 otherwise. A len of 0 gives 1.

EXAMPLES

uint8_t tag[32];
if (nqhmac(NQS256, key, keylen, msg, msglen, tag, sizeof tag) == NQOK &&
    nqcteq(tag, received, sizeof tag))
  accept();