Commit 8123ce62 authored by Mark Haines's avatar Mark Haines
Browse files

Constant time comparison for mac

parent 2f2e0340
#include <cstddef>
#include <cstdint>
namespace axolotl {
/** Clear the memory held in the buffer */
void unset(
volatile void * buffer, std::size_t buffer_length
void volatile * buffer, std::size_t buffer_length
);
/** Clear the memory backing an object */
template<typename T>
void unset(T & value) {
unset(reinterpret_cast<volatile void *>(&value), sizeof(T));
unset(reinterpret_cast<void volatile *>(&value), sizeof(T));
}
/** Check if two buffers are equal in constant time. */
bool is_equal(
std::uint8_t const * buffer_a,
std::uint8_t const * buffer_b,
std::size_t length
);
} // namespace axolotl
#include "axolotl/memory.hh"
void axolotl::unset(
volatile void * buffer, std::size_t buffer_length
void volatile * buffer, std::size_t buffer_length
) {
volatile char * pos = reinterpret_cast<volatile char *>(buffer);
volatile char * end = pos + buffer_length;
char volatile * pos = reinterpret_cast<char volatile *>(buffer);
char volatile * end = pos + buffer_length;
while (pos != end) {
*(pos++) = 0;
}
}
bool axolotl::is_equal(
std::uint8_t const * buffer_a,
std::uint8_t const * buffer_b,
std::size_t length
) {
std::uint8_t volatile result = 0;
while (length--) {
result |= (*(buffer_a++)) ^ (*(buffer_b++));
}
return result == 0;
}
......@@ -104,7 +104,7 @@ bool verify_mac(
mac
);
bool result = std::memcmp(mac, reader.mac, MAC_LENGTH) == 0;
bool result = axolotl::is_equal(mac, reader.mac, MAC_LENGTH);
axolotl::unset(mac);
return result;
}
......
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