package main

import (
    "bytes"
    "crypto/ecdsa"
    "fmt"
    "log"

    "github.com/ethereum/go-ethereum/common/hexutil"
    "github.com/ethereum/go-ethereum/crypto"
)

func main() {
    privateKey, err := crypto.HexToECDSA("fad9c8855b740a0b7ed4c221dbad0f33a83a49cad6b3fe8d5817ac83d38b6a19")
    if err != nil {
        log.Fatal(err)
    }

    publicKey := privateKey.Public()
    publicKeyECDSA, ok := publicKey.(*ecdsa.PublicKey)
    if !ok {
        log.Fatal("error casting public key to ECDSA")
    }

    publicKeyBytes := crypto.FromECDSAPub(publicKeyECDSA)

    data := []byte("decartography")
    hash := crypto.Keccak256Hash(data)
    fmt.Println(hash.Hex()) // 0xfe2b8f0bae0d344e95a421b9cc1a32ef07083cc85d007146259221fece9264a7

    signature, err := crypto.Sign(hash.Bytes(), privateKey)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(hexutil.Encode(signature))

    sigPublicKey, err := crypto.Ecrecover(hash.Bytes(), signature)
    if err != nil {
        log.Fatal(err)
    }

    matches := bytes.Equal(sigPublicKey, publicKeyBytes)
    fmt.Println(matches) // true

    sigPublicKeyECDSA, err := crypto.SigToPub(hash.Bytes(), signature)
    if err != nil {
        log.Fatal(err)
    }

    sigPublicKeyBytes := crypto.FromECDSAPub(sigPublicKeyECDSA)
    matches = bytes.Equal(sigPublicKeyBytes, publicKeyBytes)
    fmt.Println(matches) // true

    signatureNoRecoverID := signature[:len(signature)-1] // remove recovery id
    verified := crypto.VerifySignature(publicKeyBytes, hash.Bytes(), signatureNoRecoverID)
    fmt.Println(verified) // true
}