An example of the proof of work concept in Bitcoin.

gistfile1.go

package main

import (
  "fmt"
  "strconv"
  "crypto/sha256"
  "encoding/base64"
)

func main(){
  fmt.Println(findNonce([]byte("henry"), "000"))
}

func findNonce(label []byte, target string) (nonce string) {
  targetLength := len(target)
  hash := sha256.New()
  i := 0

  for {
    nonce := strconv.Itoa(i)
    hash.Write([]byte(nonce))
    md := hash.Sum(nil)
    mdStr := base64.StdEncoding.EncodeToString(md)

    if mdStr[0:targetLength] == target {
      return(nonce)
    }

    i++
  }

}