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p2p/discover: new distance metric based on sha3(id)

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The previous metric was pubkey1^pubkey2, as specified in the Kademlia
paper. We missed that EC public keys are not uniformly distributed.
Using the hash of the public keys addresses that. It also makes it
a bit harder to generate node IDs that are close to a particular node.
This commit is contained in:
Felix Lange
2015-04-27 00:50:18 +02:00
parent d457a1187d
commit 2adcc31bb4
6 changed files with 354 additions and 106 deletions
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8
p2p/discover/node.go
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@ -219,7 +219,7 @@ func recoverNodeID(hash, sig []byte) (id NodeID, err error) {
// distcmp compares the distances a->target and b->target.
// Returns -1 if a is closer to target, 1 if b is closer to target
// and 0 if they are equal.
func distcmp(target, a, b NodeID) int {
func distcmp(target, a, b common.Hash) int {
for i := range target {
da := a[i] ^ target[i]
db := b[i] ^ target[i]
@ -269,7 +269,7 @@ var lzcount = [256]int{
}
// logdist returns the logarithmic distance between a and b, log2(a ^ b).
func logdist(a, b NodeID) int {
func logdist(a, b common.Hash) int {
lz := 0
for i := range a {
x := a[i] ^ b[i]
@ -283,8 +283,8 @@ func logdist(a, b NodeID) int {
return len(a)*8 - lz
}
// randomID returns a random NodeID such that logdist(a, b) == n
func randomID(a NodeID, n int) (b NodeID) {
// hashAtDistance returns a random hash such that logdist(a, b) == n
func hashAtDistance(a common.Hash, n int) (b common.Hash) {
if n == 0 {
return a
}