otp

OTP(HOTP/TOTP) package for Golang

This is a simple OTP(HOTP/TOTP) implementation in Go that can be used with the Google Authenticator app. It only support HMAC-SHA1, HMAC-SHA256, and HMAC-SHA512.

Note: All the functions to generate and validate the OTP expect the secret to be unencoded(raw bytes). If you want to use base32encoded secret make sure to decode it first by calling otp.DecodeBase32Secret utility function. Also, there is a function to generate a random base32 encoded secret GenerateBase32Secret.

Simple OTP Example

Basic 6 digits HMAC-SHA1 HOTP

digit := otp.DigitSix
counter := uint64(0}
// generate HMAC-SHA1 TOTP code with 6 digit
otpCode, err := otp.GenerateHOTPCode(rawByteSecret, counter, digit)
fmt.Println(otp.ZeroFill(otpCode, digit))

Basic 6 digits HMAC-SHA1 TOTP with 30 seconds duration

digit := otp.DigitSix
// generate HMAC-SHA1 TOTP code with 6 digit and 30 seconds duration.
otpCode, err := otp.GenerateTOTPCode(rawByteSecret, time.Now(), digit)
fmt.Println(otp.ZeroFill(otpCode, digit))

Custom 8 Digits OTP with HMAC-SHA256/HMAC-SHA512

digit := otp.DigitEight
counter := uint64(0)
// HOTP HMAC-SHA256
otpCode, err := otp.GenerateHOTPCodeAlgo(otp.AlgoSHA256, rawByteSecret, counter, digit)
fmt.Println(otp.ZeroFill(otpCode, digit))

// TOTP HMAC-SHA512
otpCode, err = otp.GenerateTOTPCodeAlgo(otp.AlgoSHA512, rawByteSecret, time.Now(), digit)
fmt.Println(otp.ZeroFill(otpCode, digit))

TOTP for Google Authenticator

Generating Key

// This will generate key for 6 digits OTP that can be used by Google 
// Authenticator App. The period duration will always be 30 seconds.
key, err := otp.GenerateGoogleAuthKey(otp.GoogleAuthKeyParam{
			Issuer:           "Example",
			AccountName:      "alice@example.com",
			Type:             otp.TypeTOTP,
			SecretByteLength: 10,
})

// prints the key
fmt.Println(key.String()) // it returns a url encoded otp key
// Or, generates a QR code that can be scanned by the app.
GenerateQRCode(key.String()) 

Validating

secret := key.Secret // get the secret from the key
rawByteSecret, err := otp.DecodeBase32Secret(secret)
var otpInput string
fmt.Scanf("%s", &otpInput)
code, err := strconv.Atoi(otpInput)
ok, err := otp.ValidateTOTPCode(int32(code), rawByteSecret, time.Now(), otp.DigitSix)
if ok {
	// Valid OTP
}

TOTP with custom duration

Generating the code

counter := otp.GetTOTPCounter(time.Now(), 20)
otpCode, err := otp.GenerateHOTPCode(rawByteSecret, counter, digit)
fmt.Println(otp.ZeroFill(otpCode, digit))

Validating the code

var otpInput string
fmt.Scanf("%s", &otpInput)
code, err := strconv.Atoi(otpInput)
counter := otp.GetTOTPCounter(time.Now(), 20)
otpCode, err := otp.ValidateHOTPCode(rawByteSecret, counter, digit)
fmt.Println(otp.ZeroFill(otpCode, digit))