Google Authenticator: Difference between revisions

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Google Authenticator is an open-source software based two-step authentication token developed by Google. The Authenticator provides a six digit number users must provide in addition to their username and password to log into Google services. The Authenticator can also generate codes for third party applications, such as LastPass or Dropbox.

Implementation

Google provides Android,^[1] BlackBerry and iOS,^[2] versions of Authenticator. Several third party implementations are available.

Windows Phone 7.5/8: Authenticator
Windows Mobile: Google Authenticator for Windows Mobile
Java CLI: Authenticator.jar
Java GUI: JAuth
J2ME: gauthj2me lwuitgauthj2me totp-me MOTP Mobile-OTP (chinese only)
PalmOS: gauthj2me
Python: onetimepass
PHP: GoogleAuthenticator.php
Ruby: google_authenticator_auth gem (third party implementation)
webOS: GAuth
Windows: gauth4win
HTML5: html5-google-authenticator
MeeGo/Harmattan (Nokia N9): GAuth
Apache: Google Authenticator Apache Module

Technical description

Google generates an 80-bit secret key for each user. This is provided as a 16 character base32 string or as a QR code. The client creates an HMAC-SHA1 using this secret key. The message that is HMAC-ed can be:

the number of 30 second periods having elapsed since the Unix epoch; or
the counter that is incremented with each new code.

A portion of the HMAC is extracted and converted to a 6 digit code.

Pseudocode for Time OTP

 function GoogleAuthenticatorCode(string secret)
     key := base32decode(secret)
     message := current Unix time ÷ 30
     hash := HMAC-SHA1(key, message)
     offset := last nibble of hash
     truncatedHash := hash[offset..offset+3]  //4 bytes starting at the offset
     Set the first bit of truncatedHash to zero  //remove the most significant bit 
     code := truncatedHash mod 1000000
     pad code with 0 until length of code is 6
     return code

Pseudocode for Event/Counter OTP

 function GoogleAuthenticatorCode(string secret)
     key := base32decode(secret)
     message := counter encoded on 8 bytes
     hash := HMAC-SHA1(key, message)
     offset := last nibble of hash
     truncatedHash := hash[offset..offset+3]  //4 bytes starting at the offset
     Set the first bit of truncatedHash to zero  //remove the most significant bit 
     code := truncatedHash mod 1000000
     pad code with 0 until length of code is 6
     return code

Technology

Google Authenticator implements the time-based One-time Password Algorithm as defined in IETF RFC 6238, and the HMAC-based One Time Password Algorithm as defined in IETF RFC 4226.

Usage

Google Authenticator can be used for the following websites and applications:

References

External links

Google Authenticator on Google Help
Google Authenticator open source project on Google Code
Google Authenticator implementation in Python on Stack Overflow

[1] Android version of Google Authenticator

[2] OS version of Google Authenticator

[3] Added security for your App.net account

[4] UPDATE: BITSTAMP ADDS SUPPORT FOR TWO-FACTOR AUTHENTICATION

[5] Enabling Multifactor Authentication

[6] Dropbox with Google Authenticator

[7] Use Facebook’s 2-factor Authentication with Third-Party TOTP Generators

[8] LastPass with Google Authenticator

[9] Linode Manager Two-Step Authentication

[10] Registro.br HOTP/TOTP Token

[1]

@@ Line 60: / Line 60: @@
 ==Usage==
 Google Authenticator can be used for the following websites:
 * [[App.net]]<ref>[http://blog.app.net/2013/03/13/added-security-for-your-app-net-account/ Added security for your App.net account]</ref>
 * [[Amazon Web Services]]