go-otp

OTP ("One-Time Pad") Utility for Go

This simple Go package implements an OTP container to ease the process of creating and utilizing single-use tokens. One-time pads are useful in cryptology to create perfect forward secrecy systems. While this implementation does not deter you from re-using keys, it makes switching keys or "pages" out simple and easy, and lends itself well to the concept in general.

Internals

A likely use case in using OTP is generating enough "pages" of cryptographically secure random bytes to permit encrypting/decrypting many messages. In go-otp, you generate some random bytes, and then use them to create a otp.Pad. Within this pad, an internal pointer keeps track of used pads. This pointer may be passed in during creation of an otp.Pad, allowing the same pad data to be used until it has been exhausted. This makes it easy to pre-share many pages of OTP material in advance, and utilize the pages over time.

go-otp also provides Encrypt and Decrypt methods to allow seamless use of OTP pads. These methods implement combining the plaintext and crypto page using modular addition. The resulting ciphertext is information theoretically secure.

Usage

func NewPad(material []byte, pageSize int, startPage int) (*Pad, error)
type Pad
    func (p *Pad) TotalPages() int
    func (p *Pad) RemainingPages() int
    func (p *Pad) CurrentPage() int
    func (p *Pad) NextPage() error
    func (p *Pad) SetPage(page int) error
    func (p *Pad) Encrypt(payload []byte) ([]byte, error)
    func (p *Pad) Decrypt(payload []byte) ([]byte, error)

Example

Following is a basic usage example which creates enough page material to facilitate 2048 unique one-time use byte slices, each 16 bytes in size. The pad is then used to perform 2 encryption routines, and some status is printed at the end.

package main

import (
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"github.com/ryanuber/go-otp"
)

func main() {
	m := make([]byte, 16*2048)
	rand.Read(m)

	// Create a new pad with 16-byte pages. Set pointer to page 1.
	pad, err := otp.NewPad(m, 16, 1)
	if err != nil {
		fmt.Printf("%s", err)
		return
	}

	encrypted, _ := pad.Encrypt([]byte("this is a test"))
	fmt.Println(base64.StdEncoding.EncodeToString(encrypted))
	decrypted, _ := pad.Decrypt(encrypted)
	fmt.Printf("%s\n\n", decrypted)

	pad.NextPage()

	encrypted, _ = pad.Encrypt([]byte("this is a test"))
	fmt.Println(base64.StdEncoding.EncodeToString(encrypted))
	decrypted, _ = pad.Decrypt(encrypted)
	fmt.Printf("%s\n\n", decrypted)

	fmt.Printf("Total pages: %d\n", pad.TotalPages())
	fmt.Printf("Page pointer: %d\n", pad.CurrentPage())
	fmt.Printf("Remaining pages: %d\n", pad.RemainingPages())
}