diff options
| -rw-r--r-- | src/crypto/slow-hash.c | 86 |
1 files changed, 85 insertions, 1 deletions
diff --git a/src/crypto/slow-hash.c b/src/crypto/slow-hash.c index d4f27e1e1..46edb0fc1 100644 --- a/src/crypto/slow-hash.c +++ b/src/crypto/slow-hash.c @@ -166,6 +166,11 @@ STATIC INLINE void xor_blocks(uint8_t *a, const uint8_t *b) 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 +210,20 @@ 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! + * + * @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 +264,22 @@ STATIC INLINE void aes_expand_key(const uint8_t *key, uint8_t *expandedKey) ek[10] = t1; } +/* + * @brief a "pseudo" round of AES (similar to 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. + * + * @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) { @@ -376,9 +411,37 @@ 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. + * + * @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 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 +465,15 @@ 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); @@ -432,6 +501,11 @@ 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. if(useAes) @@ -454,6 +528,10 @@ 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 +556,12 @@ void cn_slow_hash(const void *data, size_t length, char *hash) oaes_free((OAES_CTX **) &aes_ctx); } + /* CryptoNight Step 5: 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 200 byte pseudorandom state array down + * to the final hash output. + */ + memcpy(state.init, text, INIT_SIZE_BYTE); hash_permutation(&state.hs); extra_hashes[state.hs.b[0] & 3](&state, 200, hash); |