http://tools.ietf.org/html/rfc4226
https://tools.ietf.org/html/rfc6238
http://blogs.forgerock.org/petermajor/2014/02/one-time-passwords-hotp-and-totp/
https://software.intel.com/en-us/android/articles/sample-code-one-time-password-otp-demo
http://www.cnblogs.com/dyingbleed/archive/2012/12/05/2803782.html
http://blogs.technet.com/b/cloudpfe/archive/2014/10/26/using-time-based-one-time-passwords-for-multi-factor-authentication-in-ad-fs-3-0.aspx
https://tools.ietf.org/html/rfc6238
http://blogs.forgerock.org/petermajor/2014/02/one-time-passwords-hotp-and-totp/
https://software.intel.com/en-us/android/articles/sample-code-one-time-password-otp-demo
http://www.cnblogs.com/dyingbleed/archive/2012/12/05/2803782.html
http://blogs.technet.com/b/cloudpfe/archive/2014/10/26/using-time-based-one-time-passwords-for-multi-factor-authentication-in-ad-fs-3-0.aspx
읽어 볼것
https://gist.github.com/zeta709/4800897a2e17c2e92680
