![]() ![]() When the button on the token is pressed, the device produces the authentication code by hashing the secret key it has and its counter value. We shall see how this is rectified later. This leads to a desynchronization between the device’s counter and the system’s counter. So, the system increments its counter only when the user enters the correct authentication code. The system cannot know how many times the button of the token is pressed. ![]() The token increments its counter every time its button is pressed to generate a new token. ![]() Thus, the system knows the secret key of the token of a particular customer. When the token is issued to a customer, the system stores the token ID in its customer database. When the hardware token is produced, the cryptographic key is written into the memory of the device and the system stores this key in a database against the device ID. The counter is separately maintained by both the token device and the system. Here, the cryptographic key is shared between the system and the device. To do so, HOTP hashes a cryptographic key and a counter, which is the data here, twice to produce the code. The HOTP algorithm uses the HMAC algorithm to generate authentication codes. Since the cryptographic key is supposed to be a secret between the sender and the recipient, then it also means that it is indeed the sender who has sent the data. A more detailed explanation of the HMAC algorithm can be found here. If the hash obtained thus is the same, then that means that the data received has not been modified during transmission. So, the recipient has to use the same key and the same data to get the exact same hash. To produce the exact hash, the same input should be used. The idea is that when the HMAC of data is sent along with the data, the recipient can repeat the HMAC algorithm using the cryptographic key that was shared with them by the sender to see if the data was received intact and that it was actually sent by the sender. A rudimentary explanation of HMAC could be that it hashes data to be transmitted with a cryptographic key twice to ensure data integrity and authenticity. To understand how this algorithm works, we need to first understand how HMAC works. So, how could a system know what number was generated by the token that was not connected to the internet? Well, this was made possible by the HOTP or HMAC-based One Time Password algorithm. After entering their password, customers had to enter this number to successfully authenticate themselves. Businesses gave their customers a small electronic device that generated a number when a button was pressed. Give us your email address and whenever I write something, you'll receive a little email in your inbox.Email Addressīefore smartphones were popular, hardware tokens that produced an HOTP code were a popular way of performing two-factor authentications. ![]()
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