totp

Documentation

Overview

Package totp implement Time-Based One-Time Password Algorithm based on RFC 6238 [1].

[1] https://tools.ietf.org/html/rfc6238

Index

• Constants
• type Protocol
  • func New(fnHash func() hash.Hash, codeDigits, timeStep int) Protocol
  • func (p *Protocol) Generate(secret []byte) (otp string, err error)
  • func (p *Protocol) GenerateN(secret []byte, n int) (listOTP []string, err error)
  • func (p *Protocol) Verify(secret []byte, token string, stepsBack int) bool

Examples

• Protocol.Verify

Constants

const (
	// DefCodeDigits default digits generated when verifying or generating
	// OTP.
	DefCodeDigits = 6
	DefTimeStep   = 30
)

Types

type Protocol

type Protocol struct {
	// contains filtered or unexported fields
}

Protocol contain methods to work with TOTP using the number of digits and time steps defined from New().

func New

func New(fnHash func() hash.Hash, codeDigits, timeStep int) Protocol

New create TOTP protocol for prover or verifier using "fnHash" as the hmac-sha hash function, "codeDigits" as the number of digits to be generated and/or verified, and "timeStep" as the time divisor.

func (*Protocol) Generate

func (p *Protocol) Generate(secret []byte) (otp string, err error)

Generate one time password using the secret and current timestamp.

func (*Protocol) GenerateN

func (p *Protocol) GenerateN(secret []byte, n int) (listOTP []string, err error)

GenerateN generate n number of passwords from (current time - N*timeStep) until the curent time.

func (*Protocol) Verify

func (p *Protocol) Verify(secret []byte, token string, stepsBack int) bool

Verify the token based on the prover secret key. It will return true if the token matched, otherwise it will return false.

The stepsBack parameter define number of steps in the pass to be checked for valid OTP. For example, if stepsBack = 2 and timeStep = 30, the time range to checking OTP is in between

(current_timestamp - (2*30)) ... current_timestamp

For security reason, the maximum stepsBack is limited to 4.

Example

secretHex := "3132333435363738393031323334353637383930"

secret, err := hex.DecodeString(secretHex)
if err != nil {
	log.Fatal(err)
}

p := New(sha1.New, DefCodeDigits, DefTimeStep)
otp, _ := p.Generate(secret)

if p.Verify(secret, otp, 1) {
	fmt.Printf("Generated token is valid.\n")
} else {
	fmt.Printf("Generated token is not valid.\n")
}

Output:

Generated token is valid.