constant_time.hh File Reference

Constant-time byte comparisons for secrets and integrity values. More...

#include <array>
#include <cstddef>
#include <cstdint>
#include <openssl/crypto.h>

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Functions
bool	keepass::detail::constant_time_eq (const void *a, std::size_t a_size, const void *b, std::size_t b_size) noexcept
	Compares two byte ranges in constant time.
template<std::size_t N>
bool	keepass::detail::constant_time_eq (const std::array< uint8_t, N > &a, const std::array< uint8_t, N > &b) noexcept
	Compares two fixed-size byte arrays in constant time.

Detailed Description

Constant-time byte comparisons for secrets and integrity values.

Function Documentation

constant_time_eq() [1/2]

template<std::size_t N>

bool keepass::detail::constant_time_eq ( const std::array< uint8_t, N > &  a, const std::array< uint8_t, N > &  b  )

inlinenoexcept

Compares two fixed-size byte arrays in constant time.

Parameters

a	First array.
b	Second array.

Returns

Whether both arrays hold identical bytes.

constant_time_eq() [2/2]

bool keepass::detail::constant_time_eq ( const void *  a, std::size_t  a_size, const void *  b, std::size_t  b_size  )

inlinenoexcept

Compares two byte ranges in constant time.

The comparison time does not depend on the content bytes: every pair of bytes is always visited, so an early-exit on the first differing byte cannot leak which position differs. The lengths are treated as public, so mismatched lengths return false immediately. It is safe to compare secrets (keys, derived keys) and integrity values (hashes, HMACs) with this helper.

Parameters

a	First byte range.
a_size	Size of the first byte range.
b	Second byte range.
b_size	Size of the second byte range.

Returns

Whether both ranges are identical.