Add a simple hash chain delay function

crypto/vdf/vdf.go

@@ -0,0 +1,23 @@
+// Note this is a proof-of-concept implementation of a delay function
+// and the security properties are not guaranteed.
+// A more secure implementation of the VDF by Wesolowski (https://eprint.iacr.org/2018/623.pdf)
+// will be done soon.
+package vdf
+
+import "golang.org/x/crypto/sha3"
+
+type VDF struct {
+	difficulty int
+	input      [32]byte
+	output     [32]byte
+	finished   chan [32]byte
+}
+
+func (vdf *VDF) execute() {
+	tempResult := vdf.input
+	for i := 0; i < vdf.difficulty; i++ {
+		tempResult = sha3.Sum256(tempResult[:])
+	}
+	vdf.output = tempResult
+	vdf.finished <- vdf.output
+}