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Merge pull request #170

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46f26ff another typo fix (David G. Andersen)
ac6bc48 fix typo (David G. Andersen)
d744dd1 More documentation (David G. Andersen)
4d493f6 initial doxygen commenting of the CryptoNight proof-of-work code (David G. Andersen)
This commit is contained in:
Riccardo Spagni 2014-10-06 10:30:39 +02:00
commit 2c739371ac
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GPG key ID: 55432DF31CCD4FCD
1 changed files with 142 additions and 5 deletions
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147
src/crypto/slow-hash.c
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@ -103,8 +103,16 @@
j = state_index(a); \
_c = _mm_load_si128(R128(&hp_state[j])); \
_a = _mm_load_si128(R128(a)); \
// dga's optimized scratchpad twiddling
/*
* An SSE-optimized implementation of the second half of CryptoNote step 3.
* After using AES to mix a scratchpad value into _c (done by the caller),
* this macro xors it with _b and stores the result back to the same index (j) that it
* loaded the scratchpad value from. It then performs a second random memory
* read/write from the scratchpad, but this time mixes the values using a 64
* bit multiply.
* This code is based upon an optimized implementation by dga.
*/
#define post_aes() \
_mm_store_si128(R128(c), _c); \
_b = _mm_xor_si128(_b, _c); \
@ -160,12 +168,21 @@ void cpuid(int CPUInfo[4], int InfoType)
}
#endif
/**
* @brief a = (a xor b), where a and b point to 128 bit values
*/
STATIC INLINE void xor_blocks(uint8_t *a, const uint8_t *b)
{
U64(a)[0] ^= U64(b)[0];
U64(a)[1] ^= U64(b)[1];
}
/**
* @brief uses cpuid to determine if the CPU supports the AES instructions
* @return true if the CPU supports AES, false otherwise
*/
STATIC INLINE int check_aes_hw(void)
{
int cpuid_results[4];
@ -205,6 +222,25 @@ STATIC INLINE void aes_256_assist2(__m128i* t1, __m128i * t3)
*t3 = _mm_xor_si128(*t3, t2);
}
/**
* @brief expands 'key' into a form it can be used for AES encryption.
*
* This is an SSE-optimized implementation of AES key schedule generation. It
* expands the key into multiple round keys, each of which is used in one round
* of the AES encryption used to fill (and later, extract randomness from)
* the large 2MB buffer. Note that CryptoNight does not use a completely
* standard AES encryption for its buffer expansion, so do not copy this
* function outside of Monero without caution! This version uses the hardware
* AESKEYGENASSIST instruction to speed key generation, and thus requires
* CPU AES support.
* For more information about these functions, see page 19 of Intel's AES instructions
* white paper:
* http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/aes-instructions-set-white-paper.pdf
*
* @param key the input 128 bit key
* @param expandedKey An output buffer to hold the generated key schedule
*/
STATIC INLINE void aes_expand_key(const uint8_t *key, uint8_t *expandedKey)
{
__m128i *ek = R128(expandedKey);
@ -245,6 +281,24 @@ STATIC INLINE void aes_expand_key(const uint8_t *key, uint8_t *expandedKey)
ek[10] = t1;
}
/*
* @brief a "pseudo" round of AES (similar to but slightly different from normal AES encryption)
*
* To fill its 2MB scratch buffer, CryptoNight uses a nonstandard implementation
* of AES encryption: It applies 10 rounds of the basic AES encryption operation
* to an input 128 bit chunk of data <in>. Unlike normal AES, however, this is
* all it does; it does not perform the initial AddRoundKey step (this is done
* in subsequent steps by aesenc_si128), and it does not use the simpler final round.
* Hence, this is a "pseudo" round - though the function actually implements 10 rounds together.
*
* Note that unlike aesb_pseudo_round, this function works on multiple data chunks.
*
* @param in a pointer to nblocks * 128 bits of data to be encrypted
* @param out a pointer to an nblocks * 128 bit buffer where the output will be stored
* @param expandedKey the expanded AES key
* @param nblocks the number of 128 blocks of data to be encrypted
*/
STATIC INLINE void aes_pseudo_round(const uint8_t *in, uint8_t *out,
const uint8_t *expandedKey, int nblocks)
{
@ -269,6 +323,20 @@ STATIC INLINE void aes_pseudo_round(const uint8_t *in, uint8_t *out,
}
}
/*
* @brief aes_pseudo_round that loads data from *in and xors it with *xor first
*
* This function performs the same operations as aes_pseudo_round, but before
* performing the encryption of each 128 bit block from <in>, it xors
* it with the corresponding block from <xor>.
*
* @param in a pointer to nblocks * 128 bits of data to be encrypted
* @param out a pointer to an nblocks * 128 bit buffer where the output will be stored
* @param expandedKey the expanded AES key
* @param xor a pointer to an nblocks * 128 bit buffer that is xored into in before encryption (in is left unmodified)
* @param nblocks the number of 128 blocks of data to be encrypted
*/
STATIC INLINE void aes_pseudo_round_xor(const uint8_t *in, uint8_t *out,
const uint8_t *expandedKey, const uint8_t *xor, int nblocks)
{
@ -327,6 +395,18 @@ BOOL SetLockPagesPrivilege(HANDLE hProcess, BOOL bEnable)
}
#endif
/**
* @brief allocate the 2MB scratch buffer using OS support for huge pages, if available
*
* This function tries to allocate the 2MB scratch buffer using a single
* 2MB "huge page" (instead of the usual 4KB page sizes) to reduce TLB misses
* during the random accesses to the scratch buffer. This is one of the
* important speed optimizations needed to make CryptoNight faster.
*
* No parameters. Updates a thread-local pointer, hp_state, to point to
* the allocated buffer.
*/
void slow_hash_allocate_state(void)
{
int state = 0;
@ -356,6 +436,10 @@ void slow_hash_allocate_state(void)
}
}
/**
*@brief frees the state allocated by slow_hash_allocate_state
*/
void slow_hash_free_state(void)
{
if(hp_state == NULL)
@ -376,9 +460,40 @@ void slow_hash_free_state(void)
hp_allocated = 0;
}
/**
* @brief the hash function implementing CryptoNight, used for the Monero proof-of-work
*
* Computes the hash of <data> (which consists of <length> bytes), returning the
* hash in <hash>. The CryptoNight hash operates by first using Keccak 1600,
* the 1600 bit variant of the Keccak hash used in SHA-3, to create a 200 byte
* buffer of pseudorandom data by hashing the supplied data. It then uses this
* random data to fill a large 2MB buffer with pseudorandom data by iteratively
* encrypting it using 10 rounds of AES per entry. After this initialization,
* it executes 500,000 rounds of mixing through the random 2MB buffer using
* AES (typically provided in hardware on modern CPUs) and a 64 bit multiply.
* Finally, it re-mixes this large buffer back into
* the 200 byte "text" buffer, and then hashes this buffer using one of four
* pseudorandomly selected hash functions (Blake, Groestl, JH, or Skein)
* to populate the output.
*
* The 2MB buffer and choice of functions for mixing are designed to make the
* algorithm "CPU-friendly" (and thus, reduce the advantage of GPU, FPGA,
* or ASIC-based implementations): the functions used are fast on modern
* CPUs, and the 2MB size matches the typical amount of L3 cache available per
* core on 2013-era CPUs. When available, this implementation will use hardware
* AES support on x86 CPUs.
*
* A diagram of the inner loop of this function can be found at
* http://www.cs.cmu.edu/~dga/crypto/xmr/cryptonight.png
*
* @param data the data to hash
* @param length the length in bytes of the data
* @param hash a pointer to a buffer in which the final 256 bit hash will be stored
*/
void cn_slow_hash(const void *data, size_t length, char *hash)
{
RDATA_ALIGN16 uint8_t expandedKey[240];
RDATA_ALIGN16 uint8_t expandedKey[240]; /* These buffers are aligned to use later with SSE functions */
uint8_t text[INIT_SIZE_BYTE];
RDATA_ALIGN16 uint64_t a[2];
@ -402,9 +517,15 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
if(hp_state == NULL)
slow_hash_allocate_state();
/* CryptoNight Step 1: Use Keccak1600 to initialize the 'state' (and 'text') buffers from the data. */
hash_process(&state.hs, data, length);
memcpy(text, state.init, INIT_SIZE_BYTE);
/* CryptoNight Step 2: Iteratively encrypt the results from keccak to fill
* the 2MB large random access buffer.
*/
if(useAes)
{
aes_expand_key(state.hs.b, expandedKey);
@ -432,15 +553,20 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
U64(b)[0] = U64(&state.k[16])[0] ^ U64(&state.k[48])[0];
U64(b)[1] = U64(&state.k[16])[1] ^ U64(&state.k[48])[1];
/* CryptoNight Step 3: Bounce randomly 1 million times through the mixing buffer,
* using 500,000 iterations of the following mixing function. Each execution
* performs two reads and writes from the mixing buffer.
*/
_b = _mm_load_si128(R128(b));
// this is ugly but the branching affects the loop somewhat so put it outside.
// Two independent versions, one with AES, one without, to ensure that
// the useAes test is only performed once, not every iteration.
if(useAes)
{
for(i = 0; i < ITER / 2; i++)
{
pre_aes();
_c = _mm_aesenc_si128(_c, _a);
// post_aes(), optimized scratchpad twiddling (credits to dga)
post_aes();
}
}
@ -454,6 +580,10 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
}
}
/* CryptoNight Step 4: Sequentially pass through the mixing buffer and use 10 rounds
* of AES encryption to mix the random data back into the 'text' buffer. 'text'
* was originally created with the output of Keccak1600. */
memcpy(text, state.init, INIT_SIZE_BYTE);
if(useAes)
{
@ -478,6 +608,13 @@ void cn_slow_hash(const void *data, size_t length, char *hash)
oaes_free((OAES_CTX **) &aes_ctx);
}
/* CryptoNight Step 5: Apply Keccak to the state again, and then
* use the resulting data to select which of four finalizer
* hash functions to apply to the data (Blake, Groestl, JH, or Skein).
* Use this hash to squeeze the state array down
* to the final 256 bit hash output.
*/
memcpy(state.init, text, INIT_SIZE_BYTE);
hash_permutation(&state.hs);
extra_hashes[state.hs.b[0] & 3](&state, 200, hash);