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.

2 files changed, 28 insertions, 36 deletions

diff --git a/node/Defaults.cpp b/node/Defaults.cpp
index 0a0003b0..18b2bdb5 100644
--- a/node/Defaults.cpp
+++ b/node/Defaults.cpp
@@ -53,21 +53,21 @@ static inline std::map< Identity,std::vector<InetAddress> > _mkSupernodeMap()
 
 	// cthulhu.zerotier.com - New York, New York, USA
 	addrs.clear();
-	if (!id.fromString("d2ba4048c3:0:cfa02701eb69e2f2c64aa498151e57f82c172036967186c93f2afbe45a64d64306f88fa1225724f6f87beabd6a0feb18c746cf4691867542e18b894390692303"))
+	if (!id.fromString("21e93d708a:0:f6bfe55675a3e66f6169eefc73187a64693a994ede68eba75c9ea65818730a2b03da67a41ce7023a68e5fcd44087529c123e802f510ee00dc9162244ccd63a88"))
 		throw std::runtime_error("invalid identity in Defaults");
 	addrs.push_back(InetAddress("198.199.73.93",ZT_DEFAULT_UDP_PORT));
 	sn[id] = addrs;
 
 	// nyarlathotep.zerotier.com - San Francisco, California, USA
 	addrs.clear();
-	if (!id.fromString("80eb92f707:0:7f0209663d815438dead321ec78c65c27fec6feeb8ccd9acc152c59066740521e45d1a1cbc5186e3773178429c4b26ab0df2c78f3e822540d70456724797f23f"))
+	if (!id.fromString("d383d43143:0:7f6fe9386bf67de895869a8a949dad651c1003d3ffb382e9971f9a1ab1513f451ecfe00c6a1c45998ab9fc9a4b4f88f06651d9323752d75eaa2a44a10125e79d"))
 		throw std::runtime_error("invalid identity in Defaults");
 	addrs.push_back(InetAddress("198.199.97.220",ZT_DEFAULT_UDP_PORT));
 	sn[id] = addrs;
 
 	// shub-niggurath.zerotier.com - Amsterdam, Netherlands
 	addrs.clear();
-	if (!id.fromString("34594c9086:0:2ac70c00cc03a078a2a8f889d61e72397f8cd684a6daecbe6350f24e0193790e118805a1673eaf57ce9f7b41f45525c995289c406461c739ccad2c93efa36746"))
+	if (!id.fromString("b6179d3e54:0:e4c7ac071b0ed0820da9cec34a5269398e7fa304bf7ded8faef8f929b247be1a6e0acc0f1ff8e6159f53fc94a797b05e27357891db854f693025e94582d8206d"))
 		throw std::runtime_error("invalid identity in Defaults");
 	addrs.push_back(InetAddress("198.211.127.172",ZT_DEFAULT_UDP_PORT));
 	sn[id] = addrs;
diff --git a/node/Identity.cpp b/node/Identity.cpp
index 0c7c13df..a180c2ba 100644
--- a/node/Identity.cpp
+++ b/node/Identity.cpp
@@ -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