Google Authenticator: Difference between revisions

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Google Authenticator is a software based two-factor authentication token developed by Google. The Authenticator provides a six digit number users must provide in addition to their username and password to log in to Google services

Implementation

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

Windows Phone 7: Authenticator
Windows Mobile: Google Authenticator for Windows Mobile
Java CLI: Authenticator.jar
Java GUI: JAuth
J2ME: gauthj2me lwuitgauthj2me Mobile-OTP
PalmOS: gauthj2me
webOS: GAuth
Windows: gauth4win

Technical description

Google generates a 80-bit secret for each user. This is provided as a 16 character base32 string or as a QR code. The client creates a HMAC-SHA1 using this secret key, with the message being the number of 30 second periods having elapsed since the Unix epoch. A portion of the HMAC is extracted and converted to a 6 digit code.

Pseudocode

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

Technology

Google Authenticator uses the time-based One-time Password Algorithm as defined in RFC 6238.

References

External links

Google Authenticator on Google Help
Google Authenticator implementation in Python on Stack Overflow

[1] OS version of Google Authenticator

[2] Android version of Google Authenticator

[1]

@@ Line 1: / Line 1: @@
 '''Google Authenticator''' is a software based [[two-factor authentication]] [[Security_token#Mobile_device_tokens|token]] developed by [[Google]]. The Authenticator provides a six digit number users must provide in addition to their username and password to log in to Google services
 ==Implementation==
 Google provides [[iOS]]<ref>[http://itunes.apple.com/app/google-authenticator/id388497605?mt=8 iOS version of Google Authenticator]</ref>, [[Blackberry]] and [[Android]]<ref>[https://market.android.com/details?id=com.google.android.apps.authenticator&hl=en Android version of Google Authenticator]</ref> versions of Authenticator. Several third party implementations are available.
 *Windows Phone 7: [http://www.windowsphone.com/en-US/apps/021dd79f-0598-e011-986b-78e7d1fa76f8 Authenticator]
 *Windows Mobile: [http://forum.xda-developers.com/showthread.php?t=956184 Google Authenticator for Windows Mobile]