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Yet another revision of this algo... yeesh... and update to supernode IDs. I think I am gonna go with this one. Seems memory-hard enough to me. I am probably procrastinating by obsessing over it.

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This commit is contained in:
Adam Ierymenko 2013-10-20 15:31:32 -04:00
parent 3c5c3280ff
commit bad043729f
4 changed files with 32 additions and 38 deletions
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58
node/Identity.cpp
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@ -39,16 +39,8 @@
// These can't be changed without a new identity type. They define the
// parameters of the hashcash hashing/searching algorithm.
// Hashcash halting criteria
#define ZT_IDENTITY_GEN_HASHCASH_FIRST_BYTE_LESS_THAN 7
// Amount of memory for memory-hardness
#define ZT_IDENTITY_GEN_MEMORY 8388608
// Step distance for mixing genmem[]
#define ZT_IDENTITY_GEN_MEMORY_MIX_STEP 1024
// Rounds used for Salsa20 step
#define ZT_IDENTITY_GEN_MEMORY 4194304
#define ZT_IDENTITY_GEN_SALSA20_ROUNDS 20
namespace ZeroTier {
@ -56,37 +48,37 @@ namespace ZeroTier {
// A memory-hard composition of SHA-512 and Salsa20 for hashcash hashing
static inline void _computeMemoryHardHash(const void *publicKey,unsigned int publicKeyBytes,void *digest,void *genmem)
{
// Hash publicKey[] to obtain Salsa20 key
// Digest publicKey[] to obtain initial digest
SHA512::hash(digest,publicKey,publicKeyBytes);
// Generate genmem[] bytes of Salsa20 key stream
// Initialize genmem[] using Salsa20 in a CBC-like configuration since
// ordinary Salsa20 is randomly seekable. This is good for a cipher
// but is not what we want for sequential memory-harndess.
memset(genmem,0,ZT_IDENTITY_GEN_MEMORY);
Salsa20 s20(digest,256,(char *)digest + 32,ZT_IDENTITY_GEN_SALSA20_ROUNDS);
s20.encrypt(genmem,genmem,ZT_IDENTITY_GEN_MEMORY);
// Do something to genmem[] that iteratively makes every value
// possibly dependent on every other value with a nontrivial
// probability. Continue to use already-initialized Salsa20 as
// a random source.
for(unsigned int i=0;i<ZT_IDENTITY_GEN_MEMORY;i+=ZT_IDENTITY_GEN_MEMORY_MIX_STEP) {
s20.encrypt((char *)genmem,(char *)genmem,64);
for(unsigned long i=64;i<ZT_IDENTITY_GEN_MEMORY;i+=64) {
unsigned long k = i - 64;
*((uint64_t *)((char *)genmem + i)) = *((uint64_t *)((char *)genmem + k));
*((uint64_t *)((char *)genmem + i + 8)) = *((uint64_t *)((char *)genmem + k + 8));
*((uint64_t *)((char *)genmem + i + 16)) = *((uint64_t *)((char *)genmem + k + 16));
*((uint64_t *)((char *)genmem + i + 24)) = *((uint64_t *)((char *)genmem + k + 24));
*((uint64_t *)((char *)genmem + i + 32)) = *((uint64_t *)((char *)genmem + k + 32));
*((uint64_t *)((char *)genmem + i + 40)) = *((uint64_t *)((char *)genmem + k + 40));
*((uint64_t *)((char *)genmem + i + 48)) = *((uint64_t *)((char *)genmem + k + 48));
*((uint64_t *)((char *)genmem + i + 56)) = *((uint64_t *)((char *)genmem + k + 56));
s20.encrypt((char *)genmem + i,(char *)genmem + i,64);
uint64_t x = Utils::ntoh(*((uint64_t *)((char *)genmem + i)));
if (!(x & 3)) {
s20.encrypt((char *)genmem + i,(char *)genmem + i,64); // also makes future salsa20 state content-dependent
for(unsigned int k=0;k<8;++k,x>>=8)
++((unsigned char *)genmem)[(uintptr_t)x % ZT_IDENTITY_GEN_MEMORY];
} else {
for(unsigned int k=0;k<8;++k,x>>=8)
--((unsigned char *)genmem)[(uintptr_t)x % ZT_IDENTITY_GEN_MEMORY];
}
}
// Mix in publicKey[] again, ensuring all entropy is used
for(unsigned int i=0;i<publicKeyBytes;++i)
((unsigned char *)genmem)[i] ^= ((const unsigned char *)publicKey)[i];
// Compute final digest from final genmem[]
SHA512::hash(digest,genmem,ZT_IDENTITY_GEN_MEMORY);
// Render final digest using genmem as a lookup table
for(unsigned long i=0;i<(ZT_IDENTITY_GEN_MEMORY / sizeof(uint64_t));) {
unsigned long idx1 = (unsigned long)(Utils::ntoh(((uint64_t *)genmem)[i++]) % (64 / sizeof(uint64_t)));
unsigned long idx2 = (unsigned long)(Utils::ntoh(((uint64_t *)genmem)[i++]) % (ZT_IDENTITY_GEN_MEMORY / sizeof(uint64_t)));
uint64_t tmp = ((uint64_t *)genmem)[idx2];
((uint64_t *)genmem)[idx2] = ((uint64_t *)digest)[idx1];
((uint64_t *)digest)[idx1] = tmp;
s20.encrypt(digest,digest,64);
}
}
// Hashcash generation halting condition -- halt when first byte is less than