move into p2p package

p2p/util.go

@@ -0,0 +1,15 @@
+package p2p
+
+import (
+	"crypto/sha256"
+)
+
+// doubleSha256 calculates sha256(sha256(b)) and returns the resulting bytes.
+func doubleSha256(b []byte) []byte {
+	hasher := sha256.New()
+	hasher.Write(b)
+	sum := hasher.Sum(nil)
+	hasher.Reset()
+	hasher.Write(sum)
+	return hasher.Sum(nil)
+}