// bslh_siphashalgorithm.h -*-C++-*-
#ifndef INCLUDED_BSLH_SIPHASHALGORITHM
#define INCLUDED_BSLH_SIPHASHALGORITHM
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
//@PURPOSE: Provide an implementation of the SipHash algorithm.
//
//@CLASSES:
// bslh::SipHashAlgorithm: functor implementing the SipHash algorithm
//
//@SEE_ALSO: bslh_hash
//
//@DESCRIPTION: 'bslh::SipHashAlgorithm' implements the SipHash algorithm.
// SipHash is an algorithm designed for speed and security. A primary use case
// for this algorithm is to provide an extra line of defense in hash tables
// (such as the hash table that is used to implement 'unordered_map') against
// malicious input that could cause Denial of Service (DoS) attacks. It is
// based on one of the finalists for the SHA-3 cryptographic hash standard.
// Full details of the hash function can be found here:
// '{https://131002.net/siphash/siphash.pdf}'. This particular implementation
// has been derived from 'siphash.h' in Howard Hinnant's work here:
// '{https://github.com/HowardHinnant/hash_append}' and as much of the original
// code as possible, including comment headers, has been preserved.
//
// This class satisfies the requirements for seeded 'bslh' hashing algorithms,
// defined in 'bslh_seededhash.h'. More information can be found in the
// package level documentation for 'bslh' (internal users can also find
// information here {TEAM BDE:USING MODULAR HASHING<GO>})
//
///Security
///--------
// SipHash is *not* a cryptographically secure hash. In the paper linked
// above, the creators of this hash function describe it as "Cryptographically
// Strong", but explicitly avoid calling it cryptographically secure. In order
// to be cryptographically secure, an algorithm must, among other things,
// provide "collision resistance". "Collision resistance" means that it should
// be difficult to find two different messages m1 and m2 such that
// 'hash(m1) == hash(m2)'. Because of the limited sized output (only 2^64
// possibilities) and the fast execution time of the algorithm, it is feasible
// to find collisions by brute force, making the algorithm not
// cryptographically secure.
//
// SipHash *is*, however, a cryptographically strong PRF (pseudo-random
// function). This means, assuming a cryptographically secure random seed is
// given, the output of this algorithm will be indistinguishable from a uniform
// random distribution. This property is enough for the algorithm to be able
// to protect a hash table from malicious Denial of Service (DoS) attacks.
//
///Denial of Service (DoS) Protection
/// - - - - - - - - - - - - - - - - -
// Given a cryptographically secure seed, this algorithm will produce hashes
// with a distribution that is indistinguishable from random. This
// distribution means that there is no way for an attacker to predict which
// keys will cause collisions, meaning that this algorithm can help mitigate
// Denial of Service (DoS) attacks on a hash table. DoS attacks occur when an
// attacker deliberately degrades the performance of the hash table by
// inserting data that will collide to the same bucket, causing an average
// constant time lookup to become a linear search. This protection is only
// effective if the seed provided is a cryptographically secure random number
// that is not available to the attacker.
//
///Speed
///-----
// This algorithm is designed to be fast in comparison to other algorithms
// making similar guarantees. It is still slower than other commonly accepted
// and used hashes such as WyHash or SpookyHash. This algorithm should only be
// used when protection from malicious input is required. Otherwise, an
// algorithm that documents better performance properties should be used, such
// as 'bslh::WyHashAlgorithm'.
//
///Hash Distribution
///-----------------
// Output hashes will be well distributed and will avalanche, which means
// changing one bit of the input will change approximately 50% of the output
// bits. This will prevent similar values from funneling to the same hash or
// bucket.
//
///Hash Consistency
///----------------
// This hash algorithm is endian-independent. The hashes produced for a given
// 16-byte key sequence and given data will be the same on big-endian and
// little-endian platforms. (In the literature the key is sometimes presented
// as a large integer or sequence of integers, such as
// '0xDEADBEEF, 0xCAFEBABE, 0x8BADF00D, 0x1BADB002', in which case care must be
// taken to supply the individual key bytes in the same order on both platforms
// if the same hash results are desired.) However, if the "given data" is not
// just a character string but has internal structure, such as being integral
// or floating-point, it is likely ordered in different ways depending on the
// platform, and thus will not hash to the same value.
//
///Usage
///-----
// This section illustrates intended usage of this component.
//
///Example: Creating and Using a Hash Table containing User Input
/// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Suppose we have any array of types that define 'operator==', and we want a
// fast way to find out if values are contained in the array. We can create a
// 'HashTable' data structure that is capable of looking up values in O(1)
// time.
//
// Further suppose that we will be storing arbitrary user input in our table.
// It is possible that an attacker with knowledge of the hashing algorithm we
// are using could specially craft input that will cause collisions in our hash
// table, degrading performance to O(n). To avoid this we will need to use a
// secure hash algorithm with a random seed. This algorithm will need to be in
// the form of a hash functor -- an object that will take objects stored in our
// array as input, and yield an integer value which is hard enough for an
// outside observer to predict that it appear random. The functor can pass the
// attributes of the 'TYPE' that are salient to hashing into the hashing
// algorithm, and then return the hash that is produced.
//
// We can use the result of the hash function to index into our array of
// 'buckets'. Each 'bucket' is simply a pointer to a value in our original
// array of 'TYPE' objects.
//
// First, we define our 'HashTable' template class, with the two type
// parameters: 'TYPE' (the type being referenced) and 'HASHER' (a functor that
// produces the hash).
//..
//
// template <class TYPE, class HASHER>
// class HashTable {
// // This class template implements a hash table providing fast lookup of
// // an external, non-owned, array of values of (template parameter)
// // 'TYPE'.
// //
// // The (template parameter) 'TYPE' shall have a transitive, symmetric
// // 'operator==' function. There is no requirement that it have any
// // kind of creator defined.
// //
// // The 'HASHER' template parameter type must be a functor with a method
// // having the following signature:
// //..
// // size_t operator()(TYPE) const;
// // -OR-
// // size_t operator()(const TYPE&) const;
// //..
// // and 'HASHER' shall have a publicly accessible default constructor
// // and destructor.
// //
// // Note that this hash table has numerous simplifications because we
// // know the size of the array and never have to resize the table.
//
// // DATA
// const TYPE *d_values; // Array of values table is to
// // hold
// size_t d_numValues; // Length of 'd_values'.
// const TYPE **d_bucketArray; // Contains ptrs into
// // 'd_values'
// size_t d_bucketArrayMask; // Will always be '2^N - 1'.
// HASHER d_hasher;
//
// private:
// // PRIVATE ACCESSORS
// bool lookup(size_t *idx,
// const TYPE& value,
// size_t hashValue) const;
// // Look up the specified 'value', having the specified 'hashValue',
// // and load its index in 'd_bucketArray' into the specified 'idx'.
// // If not found, return the vacant entry in 'd_bucketArray' where
// // it should be inserted. Return 'true' if 'value' is found and
// // 'false' otherwise.
//
// public:
// // CREATORS
// HashTable(const TYPE *valuesArray,
// size_t numValues);
// // Create a hash table referring to the specified 'valuesArray'
// // having length of the specified 'numValues'. No value in
// // 'valuesArray' shall have the same value as any of the other
// // values in 'valuesArray'
//
// ~HashTable();
// // Free up memory used by this hash table.
//
// // ACCESSORS
// bool contains(const TYPE& value) const;
// // Return true if the specified 'value' is found in the table and
// // false otherwise.
// };
//
//..
// Then, we define a 'Future' class, which holds a cstring 'name', char
// 'callMonth', and short 'callYear'. This class can be used to store custom
// futures that the users have uploaded.
//..
//
// class Future {
// // This class identifies a future contract. It tracks the name, call
// // month and year of the contract it represents, and allows equality
// // comparison.
//
// // DATA
// const char *d_name; // held, not owned
// const char d_callMonth;
// const short d_callYear;
//
// public:
// // CREATORS
// Future(const char *name, const char callMonth, const short callYear)
// : d_name(name), d_callMonth(callMonth), d_callYear(callYear)
// // Create a 'Future' object out of the specified 'name',
// // 'callMonth', and 'callYear'.
// {}
//
// Future() : d_name(""), d_callMonth('\0'), d_callYear(0)
// // Create a 'Future' with default values.
// {}
//
// // ACCESSORS
// const char * getMonth() const
// // Return the month that this future expires.
// {
// return &d_callMonth;
// }
//
// const char * getName() const
// // Return the name of this future
// {
// return d_name;
// }
//
// const short * getYear() const
// // Return the year that this future expires
// {
// return &d_callYear;
// }
//
// bool operator==(const Future& other) const
// // Compare this to the specified 'other' object and return true if
// // they are equal
// {
// return (!strcmp(d_name, other.d_name)) &&
// d_callMonth == other.d_callMonth &&
// d_callYear == other.d_callYear;
// }
// };
//
// bool operator!=(const Future& lhs, const Future& rhs)
// // Compare compare the specified 'lhs' and 'rhs' objects and return
// // true if they are not equal
// {
// return !(lhs == rhs);
// }
//
//..
// Next, we need a hash functor for 'Future'. We are going to use the
// 'SipHashAlgorithm' because, it is a secure hash algorithm that will provide
// a way to securely combine the attributes of 'Future' objects that are
// salient to hashing into one reasonable hash that an malicious user will not
// be able to predict.
//..
//
// struct HashFuture {
// // This struct is a functor that will apply the SipHashAlgorithm to
// // objects of type 'Future'.
//
// size_t operator()(const Future& future) const
// // Return the hash of the of the specified 'future'. Note that
// // this uses the 'SipHashAlgorithm' to safely combine the
// // attributes of 'Future' objects that are salient to hashing into
// // a hash that is not predictable by an attacker.
// {
// char seed[SipHashAlgorithm::k_SEED_LENGTH];
// SeedGenerator<CryptoSecureRNG> seedGenerator;
// seedGenerator.generateSeed(seed, SipHashAlgorithm::k_SEED_LENGTH);
//
// SipHashAlgorithm hash(seed);
//
// hash(future.getName(), strlen(future.getName()));
// hash(future.getMonth(), sizeof(char));
// hash(future.getYear(), sizeof(short));
//
// return static_cast<size_t>(hash.computeHash());
// }
// };
//
//..
// Then, we want to actually use our hash table on 'Future' objects. We create
// an array of 'Future's based on data that was originally from some external
// source:
//..
// Future futures[] = { Future("Swiss Franc", 'F', 2014),
// Future("US Dollar", 'G', 2015),
// Future("Canadian Dollar", 'Z', 2014),
// Future("British Pound", 'M', 2015),
// Future("Deutsche Mark", 'X', 2016),
// Future("Eurodollar", 'Q', 2017)};
// enum { NUM_FUTURES = sizeof futures / sizeof *futures };
//
// Next, we create our HashTable 'hashTable'. We pass the functor that we
// defined above as the second argument:
//
// HashTable<Future, HashFuture> hashTable(futures, NUM_FUTURES);
//..
// Now, we verify that each element in our array registers with count:
//..
// for ( int i = 0; i < 6; ++i) {
// ASSERT(hashTable.contains(futures[i]));
// }
//..
// Finally, we verify that futures not in our original array are correctly
// identified as not being in the set:
//..
// ASSERT(!hashTable.contains(Future("French Franc", 'N', 2019)));
// ASSERT(!hashTable.contains(Future("Swiss Franc", 'X', 2014)));
// ASSERT(!hashTable.contains(Future("US Dollar", 'F', 2014)));
//..
//
///Changes
///-------
// The third party code begins with the 'siphash.h' header below, and continues
// until the TYPE TRAITS banner below. Changes made to the original code
// include:
//
//: 1 Adding 'BloombergLP' and 'bslh' namespaces
//:
//: 2 Renaming 'siphash' to 'SipHashAlgorithm'
//:
//: 3 Whitespace changes for formatting
//:
//: 4 Added comments
//:
//: 5 Removed C++11 features including class member initializer, 'noexcept',
//: 'std::Uint64_t', explicit conversion operator, and an '= default'
//: constructor.
//:
//: 6 Added 'typedef' to replace removed 'std::Uint64_t'
//:
//: 7 Added 'computeHash()' to replace the removed explicit conversion
//:
//: 8 Added 'k_SEED_LENGTH' and changed the constructor to accept a
//: 'const char *'
//:
//: 9 Included headers and added 'include' guards
//:
//: 10 Changed variables to use 'size_t' rather than 'unsigned int'
//
///Third-Party Documentation
///-------------------------
//------------------------------- siphash.h -----------------------------------
//
// This software is in the public domain. The only restriction on its use is
// that no one can remove it from the public domain by claiming ownership of
// it, including the original authors.
//
// There is no warranty of correctness on the software contained herein. Use
// at your own risk.
//
// Derived from:
//
// SipHash reference C implementation
//
// Written in 2012 by Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
// Daniel J. Bernstein <djb@cr.yp.to>
//
// To the extent possible under law, the author(s) have dedicated all copyright
// and related and neighboring rights to this software to the public domain
// worldwide. This software is distributed without any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication along
// with this software. If not, see
// <http://creativecommons.org/publicdomain/zero/1.0/>.
//
//-----------------------------------------------------------------------------
#include <bslscm_version.h>
#include <bslmf_isbitwisemoveable.h>
#include <bsls_types.h>
#include <stddef.h> // for 'size_t'
namespace BloombergLP {
namespace bslh {
// ============================
// class bslh::SipHashAlgorithm
// ============================
class SipHashAlgorithm {
// This class wraps an implementation of the "SipHash" algorithm in an
// interface that is usable in the modular hashing system in 'bslh'.
private:
// PRIVATE TYPES
typedef bsls::Types::Uint64 Uint64;
// Typedef for a 64-bit integer type used in the hashing algorithm.
// DATA
Uint64 d_v0;
Uint64 d_v1;
Uint64 d_v2;
Uint64 d_v3;
// Stores the intermediate state of the algorithm as values are
// accumulated
union {
Uint64 d_alignment;
// Provides alignment
unsigned char d_buf [8];
// Used to buffer data until we have enough to do a full round of
// computation as specified by the algorithm.
};
size_t d_bufSize;
// The length of the data currently stored in the buffer.
size_t d_totalLength;
// The total length of all data that has been passed into the
// algorithm.
// NOT IMPLEMENTED
SipHashAlgorithm(const SipHashAlgorithm& original); // = delete;
// Do not allow copy construction.
SipHashAlgorithm& operator=(const SipHashAlgorithm& rhs); // = delete;
// Do not allow assignment.
public:
// TYPES
typedef Uint64 result_type;
// Typedef indicating the value type returned by this algorithm.
// CONSTANTS
enum { k_SEED_LENGTH = 16 }; // Seed length in bytes.
// CREATORS
explicit SipHashAlgorithm(const char *seed);
// Create a 'bslh::SipHashAlgorithm', seeded with a 128-bit
// ('k_SEED_LENGTH' bytes) seed pointed to by the specified 'seed'.
// Each bit of the supplied seed will contribute to the final hash
// produced by 'computeHash()'. The behaviour is undefined unless
// 'seed' points to at least 16 bytes of initialized memory. Note that
// if data in 'seed' is not random, all guarantees of security and
// Denial of Service (DoS) protection are void.
//! ~SipHashAlgorithm() = default;
// Destroy this object.
// MANIPULATORS
void operator()(const void *data, size_t numBytes);
// Incorporate the specified 'data', of at least the specified
// 'numBytes', into the internal state of the hashing algorithm. Every
// bit of data incorporated into the internal state of the algorithm
// will contribute to the final hash produced by 'computeHash()'. The
// same hash will be produced regardless of whether a sequence of bytes
// is passed in all at once or through multiple calls to this member
// function. Input where 'numBytes' is 0 will have no effect on the
// internal state of the algorithm. The behaviour is undefined unless
// 'data' points to a valid memory location with at least 'numBytes'
// bytes of initialized memory.
result_type computeHash();
// Return the finalized version of the hash that has been accumulated.
// Note that this changes the internal state of the object, so calling
// 'computeHash()' multiple times in a row will return different
// results, and only the first result returned will match the expected
// result of the algorithm. Also note that a value will be returned,
// even if data has not been passed into 'operator()'
};
} // close package namespace
// ============================================================================
// TYPE TRAITS
// ============================================================================
namespace bslmf {
template <>
struct IsBitwiseMoveable<bslh::SipHashAlgorithm>
: bsl::true_type {};
} // close namespace bslmf
} // close enterprise namespace
#endif
// ----------------------------------------------------------------------------
// Copyright 2014 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------