2fa.go

package base64Captcha

import (
	"crypto/hmac"
	"crypto/sha1"
	"encoding/base32"
	"encoding/binary"
	"strings"
	"time"
	"unicode"
)

const counterLen = 20

func noSpace(r rune) rune {
	if unicode.IsSpace(r) {
		return -1
	}
	return r
}

func decodeKey(key string) ([]byte, error) {
	return base32.StdEncoding.DecodeString(strings.ToUpper(key))
}

func hotp(key []byte, counter uint64, digits int) int {
	h := hmac.New(sha1.New, key)
	binary.Write(h, binary.BigEndian, counter)
	sum := h.Sum(nil)
	v := binary.BigEndian.Uint32(sum[sum[len(sum)-1]&0x0F:]) & 0x7FFFFFFF
	d := uint32(1)
	for i := 0; i < digits && i < 8; i++ {
		d *= 10
	}
	return int(v % d)
}

func totp(key []byte, t time.Time, digits int) int {
	return hotp(key, uint64(t.UnixNano())/30e9, digits)
}