bitcoin-public-point-to-address.go

package main

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"

	"golang.org/x/crypto/ripemd160"
)

// Point is a type for a bitcoin public point.
type Point struct {
	x, y [32]byte
}

// SetHex takes two hexidecimal strings and decodes them into the receiver.
func (p *Point) SetHex(x, y string) error {
	if len(x) != 64 || len(y) != 64 {
		return errors.New("invalid hex string length")
	}
	if _, err := hex.Decode(p.x[:], []byte(x)); err != nil {
		return err
	}
	_, err := hex.Decode(p.y[:], []byte(y))
	return err
}

// A25 type in common with Bitcoin/address validation task.
type A25 [25]byte

// doubleSHA256 method in common with Bitcoin/address validation task.
func (a *A25) doubleSHA256() []byte {
	h := sha256.New()
	h.Write(a[:21])
	d := h.Sum([]byte{})
	h = sha256.New()
	h.Write(d)
	return h.Sum(d[:0])
}

// UpdateChecksum computes the address checksum on the first 21 bytes and
// stores the result in the last 4 bytes.
func (a *A25) UpdateChecksum() {
	copy(a[21:], a.doubleSHA256())
}

// SetPoint takes a public point and generates the corresponding address
// into the receiver, complete with valid checksum.
func (a *A25) SetPoint(p *Point) {
	c := [65]byte{4}
	copy(c[1:], p.x[:])
	copy(c[33:], p.y[:])
	h := sha256.New()
	h.Write(c[:])
	s := h.Sum([]byte{})
	h = ripemd160.New()
	h.Write(s)
	h.Sum(a[1:1])
	a.UpdateChecksum()
}

// Tmpl in common with Bitcoin/address validation task.
var tmpl = []byte("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz")

// A58 returns a base58 encoded bitcoin address corresponding to the receiver.
// Code adapted from the C solution to this task.
func (a *A25) A58() []byte {
	var out [34]byte
	for n := 33; n >= 0; n-- {
		c := 0
		for i := 0; i < 25; i++ {
			c = c*256 + int(a[i])
			a[i] = byte(c / 58)
			c %= 58
		}
		out[n] = tmpl[c]
	}
	i := 1
	for i < 34 && out[i] == '1' {
		i++
	}
	return out[i-1:]
}

func main() {
	// parse hex into point object
	var p Point
	err := p.SetHex(
		"50863AD64A87AE8A2FE83C1AF1A8403CB53F53E486D8511DAD8A04887E5B2352",
		"2CD470243453A299FA9E77237716103ABC11A1DF38855ED6F2EE187E9C582BA6")
	if err != nil {
		fmt.Println(err)
		return
	}
	// generate address object from point
	var a A25
	a.SetPoint(&p)
	// show base58 representation
	fmt.Println(string(a.A58()))
}

//\Bitcoin-public-point-to-address\bitcoin-public-point-to-address.go