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Start refactoring hashing.

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This commit moves some of the hash datastructures and code from
util.cc into Hash.cc - where it seems more appropriate.

It also starts to make more Keyed hash functions available - still
using siphash as the default 64 bit keyed hash, but also making
128 and 256 bit highway hashes available.

There already are a few other functions that are defined but not
yet implemented - these will be "static" keyed hashes - which use
an installation specific key. These will be used to, e.g., get
rid of md5 hashing for the generation of file UIDs.
This commit is contained in:
Johanna Amann 2020-04-24 17:11:16 -07:00
parent d34532f847
commit 360c06a3f8
7 changed files with 123 additions and 67 deletions
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53
src/Hash.h
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@ -1,5 +1,22 @@
// See the file "COPYING" in the main distribution directory for copyright.
/***
* This file contains functions to generate hashes used keyed hash functions.
* Keyed hash functions make it difficult/impossible to find information about the
* output of a hash when the key is unknown to the attacker. This fact holds, even
* when the input value us known.
*
* We use these kinds of hashes heavily internally - e.g. for scriptland hash generation.
* It is important that these hashes are not easily guessable to prevent complexity attacks.
*
* The HashKey class is the actual class that is used to generate Hash keys that are used internally,
* e.g. for lookups in hash-tables; the Hashes are also used for connection ID generation.
*
* This means that the hashes created by most functions in this file will be different each run, unless
* a seed file is used. There are a few functions that create hashes that are static over runs
* and use an installation-wide seed value; these are specifically called out.
*/
#pragma once
#include "util.h" // for bro_int_t
@ -8,7 +25,43 @@
class BroString;
// to allow bro_md5_hmac access to the hmac seed
#include "ZeekArgs.h"
class Val;
class Frame;
namespace BifFunc {
extern Val* bro_md5_hmac(Frame* frame, const zeek::Args*);
}
typedef uint64_t hash_t;
typedef uint64_t hash64_t;
typedef uint64_t hash128_t[2];
typedef uint64_t hash256_t[4];
class KeyedHash {
public:
constexpr static int SEED_INIT_SIZE = 20;
static void InitializeSeeds(const std::array<uint32_t, SEED_INIT_SIZE>& seed_data);
static bool IsInitialized() { return seeds_initialized; }
static hash64_t Hash64(const void* bytes, uint64_t size);
static void Hash128(const void* bytes, uint64_t size, hash128_t* result);
static void Hash256(const void* bytes, uint64_t size, hash256_t* result);
static hash64_t StaticHash64(const void* bytes, uint64_t size);
static void StaticHash128(const void* bytes, uint64_t size, hash128_t* result);
static void StaticHash256(const void* bytes, uint64_t size, hash256_t* result);
private:
// actually HHKey
alignas(32) inline static uint64_t shared_highwayhash_key[4];
// actually HH_U64, which has the same type
alignas(16) inline static unsigned long long shared_siphash_key[2];
inline static uint8_t shared_hmac_md5_key[16];
inline static bool seeds_initialized = false;
friend void hmac_md5(size_t size, const unsigned char* bytes, unsigned char digest[16]);
friend Val* BifFunc::bro_md5_hmac(Frame* frame, const zeek::Args*);
};
typedef enum {
HASH_KEY_INT,