zeek/src/Hash.cc

// See the file "COPYING" in the main distribution directory for copyright.

// The hash function works as follows:
//
// 1) For short data we have a number of universal hash functions:
// UHASH_CW (ax + b (mod p)), H3, Dietzfelbinger and UMAC_NH (UMAC_NH is
// not as strongly universal as the others, but probably enough). All
// these functions require number of random bits linear to the data
// length. And we use them for data no longer than UHASH_KEY_SIZE.
// They are faster than HMAC/MD5 used for longer data, and most hash
// operations are on short data.
//
// 2) As a fall-back, we use HMAC/MD5 (keyed MD5) for data of arbitrary
// length. MD5 is used as a scrambling scheme so that it is difficult
// for the adversary to construct conflicts, though I do not know if
// HMAC/MD5 is provably universal.

#include "bro-config.h"

#include "Hash.h"
#include "Reporter.h"

#include "siphash24.h"

void init_hash_function()
	{
	// Make sure we have already called init_random_seed().
	if ( ! (hmac_key_set && siphash_key_set) )
		reporter->InternalError("Bro's hash functions aren't fully initialized");
	}

HashKey::HashKey(bro_int_t i)
	{
	key_u.i = i;
	key = (void*) &key_u;
	size = sizeof(i);
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(bro_uint_t u)
	{
	key_u.i = bro_int_t(u);
	key = (void*) &key_u;
	size = sizeof(u);
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(uint32 u)
	{
	key_u.u32 = u;
	key = (void*) &key_u;
	size = sizeof(u);
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(const uint32 u[], int n)
	{
	size = n * sizeof(u[0]);
	key = (void*) u;
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(double d)
	{
	union {
		double d;
		int i[2];
	} u;

	key_u.d = u.d = d;
	key = (void*) &key_u;
	size = sizeof(d);
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(const void* p)
	{
	key_u.p = p;
	key = (void*) &key_u;
	size = sizeof(p);
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(const char* s)
	{
	size = strlen(s);	// note - skip final \0
	key = (void*) s;
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(const BroString* s)
	{
	size = s->Len();
	key = (void*) s->Bytes();
	hash = HashBytes(key, size);
	is_our_dynamic = 0;
	}

HashKey::HashKey(int copy_key, void* arg_key, int arg_size)
	{
	size = arg_size;
	is_our_dynamic = 1;

	if ( copy_key )
		{
		key = (void*) new char[size];
		memcpy(key, arg_key, size);
		}
	else
		key = arg_key;

	hash = HashBytes(key, size);
	}

HashKey::HashKey(const void* arg_key, int arg_size, hash_t arg_hash)
	{
	size = arg_size;
	hash = arg_hash;
	key = CopyKey(arg_key, size);
	is_our_dynamic = 1;
	}

HashKey::HashKey(const void* arg_key, int arg_size, hash_t arg_hash,
		bool /* dont_copy */)
	{
	size = arg_size;
	hash = arg_hash;
	key = const_cast<void*>(arg_key);
	is_our_dynamic = 0;
	}

HashKey::HashKey(const void* bytes, int arg_size)
	{
	size = arg_size;
	key = CopyKey(bytes, size);
	hash = HashBytes(key, size);
	is_our_dynamic = 1;
	}

void* HashKey::TakeKey()
	{
	if ( is_our_dynamic )
		{
		is_our_dynamic = 0;
		return key;
		}
	else
		return CopyKey(key, size);
	}

void* HashKey::CopyKey(const void* k, int s) const
	{
	void* k_copy = (void*) new char[s];
	memcpy(k_copy, k, s);
	return k_copy;
	}

hash_t HashKey::HashBytes(const void* bytes, int size)
	{
	if ( size <= UHASH_KEY_SIZE )
		{
		hash_t digest;
		siphash(&digest, (const uint8_t *)bytes, size, shared_siphash_key);
		return digest;
		}

	// Fall back to HMAC/MD5 for longer data (which is usually rare).
	assert(sizeof(hash_t) == 8);
	hash_t digest[2]; // 2x hash_t (uint64) = 128 bits = 32 hex chars = sizeof md5
	hmac_md5(size, (const unsigned char*) bytes, (unsigned char*) digest);
	return digest[0];
	}