OneTimePassword

TOTP and HOTP one-time passwords for iOS

The OneTimePassword library is the core of Authenticator. It can generate both time-based and counter-based one-time passwords as standardized in RFC 4226 and RFC 6238. It can also read and generate the "otpauth://" URLs commonly used to set up OTP tokens, and can save and load tokens to and from the iOS secure keychain.

Installation

Carthage

Add the following line to your Cartfile:

github "mattrubin/OneTimePassword" ~> 4.0

Then run carthage update OneTimePassword to install the latest version of the framework.

Be sure to check the Carthage README file for the latest instructions on adding frameworks to an application.

SPM

Add the following line to the dependencies section of your package manifest:

.package(url: "https://github.com/mattrubin/OneTimePassword.git", from: "4.0.0"),

Then add "OneTimePassword" to the dependencies array of any target which should be linked with this library.

Usage

The latest version of OneTimePassword compiles with Swift 5. To use OneTimePassword with earlier versions of Swift, check out the swift-4.2, swift-4, swift-3, and swift-2.3 branches. To use OneTimePassword in an Objective-C based project, check out the objc branch and the 1.x releases.

Create a Token

The Generator struct contains the parameters necessary to generate a one-time password. The Token struct associates a generator with a name and an issuer string.

To initialize a token with an otpauth:// url:

if let token = Token(url: url) {
    print("Password: \(token.currentPassword)")
} else {
    print("Invalid token URL")
}

To create a generator and a token from user input:

This example assumes the user provides the secret as a Base32-encoded string. To use the decoding function seen below, add import Base32 to the top of your Swift file.

let name = "..."
let issuer = "..."
let secretString = "..."

guard let secretData = MF_Base32Codec.data(fromBase32String: secretString),
    !secretData.isEmpty else {
        print("Invalid secret")
        return nil
}

guard let generator = Generator(
    factor: .timer(period: 30),
    secret: secretData,
    algorithm: .sha1,
    digits: 6) else {
        print("Invalid generator parameters")
        return nil
}

let token = Token(name: name, issuer: issuer, generator: generator)
return token

Generate a One-Time Password

To generate the current password:

let password = token.currentPassword

To generate the password at a specific point in time:

let time = Date(timeIntervalSince1970: ...)
do {
    let passwordAtTime = try token.generator.password(at: time)
    print("Password at time: \(passwordAtTime)")
} catch {
    print("Cannot generate password for invalid time \(time)")
}

Persistence

Token persistence is managed by the Keychain class, which represents the iOS system keychain.

let keychain = Keychain.sharedInstance

The PersistentToken struct represents a Token that has been saved to the keychain, and associates a token with a keychain-provided data identifier.

To save a token to the keychain:

do {
    let persistentToken = try keychain.add(token)
    print("Saved to keychain with identifier: \(persistentToken.identifier)")
} catch {
    print("Keychain error: \(error)")
}

To retrieve a token from the keychain:

do {
    if let persistentToken = try keychain.persistentToken(withIdentifier: identifier) {
        print("Retrieved token: \(persistentToken.token)")
    }
    // Or...
    let persistentTokens = try keychain.allPersistentTokens()
    print("All tokens: \(persistentTokens.map({ $0.token }))")
} catch {
    print("Keychain error: \(error)")
}

To update a saved token in the keychain:

do {
    let updatedPersistentToken = try keychain.update(persistentToken, with: token)
    print("Updated token: \(updatedPersistentToken)")
} catch {
    print("Keychain error: \(error)")
}

To delete a token from the keychain:

do {
    try keychain.delete(persistentToken)
    print("Deleted token.")
} catch {
    print("Keychain error: \(error)")
}

License

OneTimePassword was created by Matt Rubin and the OneTimePassword authors and is released under the MIT License.