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OTP Sharp

This is an implementation of HOTP and TOTP which are commonly used for multi factor authentication by using a shared key between the client and the server to generate and verify one time use codes. This library is capable of generating and verifying both TOTP and HOTP authentication codes. The calculations in this library are known to be compatible with Google 2-Step Verification and consequently the Google Authenticator smartphone app. It is also known to be able to generate codes for Amazon Web Services Multi Factor Authentication and Dropbox 2 step authentication. It should work with any other service or client that is RFC compliant.

This library is released under an MIT license. No warranty is provided as to the correctness of the library and the consumer of the library assumes all risk for the use thereof, as per the MIT license.

Every effort has gone into implementing this library in accordance with the RFCs mentioned above. However it is up to the users of this library to read through the RFCs and ensure that this implementation is in accordance with the security procedures outlined therein.

The implementation includes the code calculation as well as simple verification. Persistence of the keys, secure key storage, ensuring that a single code can't be validated multiple times and other things are not a part of this library. Thus far those functions (and any others mentioned in the RFCs) are up to the consumer of this library.

For documentation please visit the project website.

To install OTP Sharp, run the following command in the Package Manager Console

Install-Package OtpSharp -Version

Release Notes

1.3 Sign the assembly

1.2 extract base32 functionality into seperate nuget package (Base32). Implement FromUrl functionality

1.1 Change the Key api to no longer require returning the plaintext key. (will break any custom key implementations). Move the get URL from the Otp to a static Url type.

1.0.6 Change the computed values from ints to padded strings. (Breaking change but is a more appropriate API)

1.0.5 Change package name from OTP-Sharp to OtpSharp

1.0.4 Changed the Protected Key API to be more explicit (may break existing direct useage of the protected key)

The protected key no longer implicitly causes side effects (destroying the plaintext key provided must be done explicitly)

Added a time correction class with experimental NTP abilities.



Devin Martin


Copyright 2012-2013 Devin Martin



Version History

Version Downloads Last updated
OTP Sharp (this version) 22,145 Monday, November 16, 2015
OTP Sharp 7,427 Saturday, January 17, 2015
OTP Sharp 2,366 Sunday, July 13, 2014
OTP Sharp 130 Saturday, July 12, 2014
OTP Sharp 1,437 Friday, October 25, 2013
OTP Sharp 255 Friday, August 9, 2013
OTP Sharp 188 Monday, July 29, 2013
OTP Sharp 339 Tuesday, March 12, 2013
OTP Sharp 169 Tuesday, March 12, 2013
OTP Sharp 162 Tuesday, March 12, 2013
OTP Sharp 163 Monday, March 11, 2013
OTP Sharp 185 Friday, March 8, 2013
OTP Sharp 176 Saturday, March 2, 2013
OTP Sharp 1.0.5 219 Friday, March 1, 2013