Merge pull request #170
46f26ffanother typo fix (David G. Andersen)ac6bc48fix typo (David G. Andersen)d744dd1More documentation (David G. Andersen)4d493f6initial doxygen commenting of the CryptoNight proof-of-work code (David G. Andersen)
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Riccardo Spagni
commit
2c739371ac
@ -103,8 +103,16 @@
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j = state_index(a); \
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_c = _mm_load_si128(R128(&hp_state[j])); \
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_a = _mm_load_si128(R128(a)); \
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// dga's optimized scratchpad twiddling
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/*
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* An SSE-optimized implementation of the second half of CryptoNote step 3.
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* After using AES to mix a scratchpad value into _c (done by the caller),
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* this macro xors it with _b and stores the result back to the same index (j) that it
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* loaded the scratchpad value from. It then performs a second random memory
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* read/write from the scratchpad, but this time mixes the values using a 64
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* bit multiply.
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* This code is based upon an optimized implementation by dga.
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*/
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#define post_aes() \
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_mm_store_si128(R128(c), _c); \
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_b = _mm_xor_si128(_b, _c); \
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@ -160,12 +168,21 @@ void cpuid(int CPUInfo[4], int InfoType)
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}
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#endif
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/**
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* @brief a = (a xor b), where a and b point to 128 bit values
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*/
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STATIC INLINE void xor_blocks(uint8_t *a, const uint8_t *b)
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{
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U64(a)[0] ^= U64(b)[0];
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U64(a)[1] ^= U64(b)[1];
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}
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/**
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* @brief uses cpuid to determine if the CPU supports the AES instructions
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* @return true if the CPU supports AES, false otherwise
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*/
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STATIC INLINE int check_aes_hw(void)
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{
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int cpuid_results[4];
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@ -205,6 +222,25 @@ STATIC INLINE void aes_256_assist2(__m128i* t1, __m128i * t3)
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*t3 = _mm_xor_si128(*t3, t2);
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}
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/**
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* @brief expands 'key' into a form it can be used for AES encryption.
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*
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* This is an SSE-optimized implementation of AES key schedule generation. It
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* expands the key into multiple round keys, each of which is used in one round
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* of the AES encryption used to fill (and later, extract randomness from)
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* the large 2MB buffer. Note that CryptoNight does not use a completely
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* standard AES encryption for its buffer expansion, so do not copy this
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* function outside of Monero without caution! This version uses the hardware
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* AESKEYGENASSIST instruction to speed key generation, and thus requires
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* CPU AES support.
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* For more information about these functions, see page 19 of Intel's AES instructions
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* white paper:
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* http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/aes-instructions-set-white-paper.pdf
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*
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* @param key the input 128 bit key
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* @param expandedKey An output buffer to hold the generated key schedule
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*/
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STATIC INLINE void aes_expand_key(const uint8_t *key, uint8_t *expandedKey)
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{
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__m128i *ek = R128(expandedKey);
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@ -245,6 +281,24 @@ STATIC INLINE void aes_expand_key(const uint8_t *key, uint8_t *expandedKey)
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ek[10] = t1;
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}
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/*
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* @brief a "pseudo" round of AES (similar to but slightly different from normal AES encryption)
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*
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* To fill its 2MB scratch buffer, CryptoNight uses a nonstandard implementation
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* of AES encryption: It applies 10 rounds of the basic AES encryption operation
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* to an input 128 bit chunk of data <in>. Unlike normal AES, however, this is
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* all it does; it does not perform the initial AddRoundKey step (this is done
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* in subsequent steps by aesenc_si128), and it does not use the simpler final round.
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* Hence, this is a "pseudo" round - though the function actually implements 10 rounds together.
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*
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* Note that unlike aesb_pseudo_round, this function works on multiple data chunks.
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*
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* @param in a pointer to nblocks * 128 bits of data to be encrypted
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* @param out a pointer to an nblocks * 128 bit buffer where the output will be stored
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* @param expandedKey the expanded AES key
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* @param nblocks the number of 128 blocks of data to be encrypted
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*/
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STATIC INLINE void aes_pseudo_round(const uint8_t *in, uint8_t *out,
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const uint8_t *expandedKey, int nblocks)
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{
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@ -269,6 +323,20 @@ STATIC INLINE void aes_pseudo_round(const uint8_t *in, uint8_t *out,
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}
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}
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/*
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* @brief aes_pseudo_round that loads data from *in and xors it with *xor first
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*
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* This function performs the same operations as aes_pseudo_round, but before
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* performing the encryption of each 128 bit block from <in>, it xors
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* it with the corresponding block from <xor>.
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*
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* @param in a pointer to nblocks * 128 bits of data to be encrypted
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* @param out a pointer to an nblocks * 128 bit buffer where the output will be stored
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* @param expandedKey the expanded AES key
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* @param xor a pointer to an nblocks * 128 bit buffer that is xored into in before encryption (in is left unmodified)
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* @param nblocks the number of 128 blocks of data to be encrypted
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*/
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STATIC INLINE void aes_pseudo_round_xor(const uint8_t *in, uint8_t *out,
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const uint8_t *expandedKey, const uint8_t *xor, int nblocks)
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{
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@ -327,6 +395,18 @@ BOOL SetLockPagesPrivilege(HANDLE hProcess, BOOL bEnable)
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}
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#endif
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/**
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* @brief allocate the 2MB scratch buffer using OS support for huge pages, if available
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*
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* This function tries to allocate the 2MB scratch buffer using a single
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* 2MB "huge page" (instead of the usual 4KB page sizes) to reduce TLB misses
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* during the random accesses to the scratch buffer. This is one of the
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* important speed optimizations needed to make CryptoNight faster.
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*
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* No parameters. Updates a thread-local pointer, hp_state, to point to
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* the allocated buffer.
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*/
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void slow_hash_allocate_state(void)
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{
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int state = 0;
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@ -356,6 +436,10 @@ void slow_hash_allocate_state(void)
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}
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}
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/**
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*@brief frees the state allocated by slow_hash_allocate_state
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*/
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void slow_hash_free_state(void)
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{
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if(hp_state == NULL)
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@ -376,9 +460,40 @@ void slow_hash_free_state(void)
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hp_allocated = 0;
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}
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/**
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* @brief the hash function implementing CryptoNight, used for the Monero proof-of-work
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*
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* Computes the hash of <data> (which consists of <length> bytes), returning the
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* hash in <hash>. The CryptoNight hash operates by first using Keccak 1600,
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* the 1600 bit variant of the Keccak hash used in SHA-3, to create a 200 byte
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* buffer of pseudorandom data by hashing the supplied data. It then uses this
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* random data to fill a large 2MB buffer with pseudorandom data by iteratively
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* encrypting it using 10 rounds of AES per entry. After this initialization,
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* it executes 500,000 rounds of mixing through the random 2MB buffer using
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* AES (typically provided in hardware on modern CPUs) and a 64 bit multiply.
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* Finally, it re-mixes this large buffer back into
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* the 200 byte "text" buffer, and then hashes this buffer using one of four
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* pseudorandomly selected hash functions (Blake, Groestl, JH, or Skein)
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* to populate the output.
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*
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* The 2MB buffer and choice of functions for mixing are designed to make the
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* algorithm "CPU-friendly" (and thus, reduce the advantage of GPU, FPGA,
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* or ASIC-based implementations): the functions used are fast on modern
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* CPUs, and the 2MB size matches the typical amount of L3 cache available per
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* core on 2013-era CPUs. When available, this implementation will use hardware
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* AES support on x86 CPUs.
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*
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* A diagram of the inner loop of this function can be found at
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* http://www.cs.cmu.edu/~dga/crypto/xmr/cryptonight.png
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*
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* @param data the data to hash
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* @param length the length in bytes of the data
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* @param hash a pointer to a buffer in which the final 256 bit hash will be stored
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*/
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void cn_slow_hash(const void *data, size_t length, char *hash)
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{
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RDATA_ALIGN16 uint8_t expandedKey[240];
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RDATA_ALIGN16 uint8_t expandedKey[240]; /* These buffers are aligned to use later with SSE functions */
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uint8_t text[INIT_SIZE_BYTE];
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RDATA_ALIGN16 uint64_t a[2];
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@ -402,9 +517,15 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
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if(hp_state == NULL)
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slow_hash_allocate_state();
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/* CryptoNight Step 1: Use Keccak1600 to initialize the 'state' (and 'text') buffers from the data. */
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hash_process(&state.hs, data, length);
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memcpy(text, state.init, INIT_SIZE_BYTE);
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/* CryptoNight Step 2: Iteratively encrypt the results from keccak to fill
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* the 2MB large random access buffer.
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*/
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if(useAes)
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{
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aes_expand_key(state.hs.b, expandedKey);
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@ -432,15 +553,20 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
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U64(b)[0] = U64(&state.k[16])[0] ^ U64(&state.k[48])[0];
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U64(b)[1] = U64(&state.k[16])[1] ^ U64(&state.k[48])[1];
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/* CryptoNight Step 3: Bounce randomly 1 million times through the mixing buffer,
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* using 500,000 iterations of the following mixing function. Each execution
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* performs two reads and writes from the mixing buffer.
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*/
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_b = _mm_load_si128(R128(b));
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// this is ugly but the branching affects the loop somewhat so put it outside.
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// Two independent versions, one with AES, one without, to ensure that
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// the useAes test is only performed once, not every iteration.
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if(useAes)
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{
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for(i = 0; i < ITER / 2; i++)
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{
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pre_aes();
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_c = _mm_aesenc_si128(_c, _a);
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// post_aes(), optimized scratchpad twiddling (credits to dga)
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post_aes();
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}
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}
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@ -454,6 +580,10 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
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}
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}
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/* CryptoNight Step 4: Sequentially pass through the mixing buffer and use 10 rounds
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* of AES encryption to mix the random data back into the 'text' buffer. 'text'
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* was originally created with the output of Keccak1600. */
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memcpy(text, state.init, INIT_SIZE_BYTE);
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if(useAes)
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{
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@ -478,6 +608,13 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
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oaes_free((OAES_CTX **) &aes_ctx);
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}
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/* CryptoNight Step 5: Apply Keccak to the state again, and then
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* use the resulting data to select which of four finalizer
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* hash functions to apply to the data (Blake, Groestl, JH, or Skein).
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* Use this hash to squeeze the state array down
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* to the final 256 bit hash output.
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*/
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memcpy(state.init, text, INIT_SIZE_BYTE);
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hash_permutation(&state.hs);
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extra_hashes[state.hs.b[0] & 3](&state, 200, hash);
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