A security token is a peripheral device used to gain access to an electronically restricted resource. The token is used in addition to, or in place of, a password. Examples of security tokens include wireless key cards used to open locked doors, a banking token used as a digital authenticator for signing in to online banking, or signing transactions such as wire transfers. Security tokens can be used to store information such as passwords, cryptographic keys used to generate digital signatures, or biometric data (such as fingerprints). Some designs incorporate tamper resistant packaging, while others may include small keypads to allow entry of a PIN or a simple button to start a generation routine with some display capability to show a generated key number. Connected tokens utilize a variety of interfaces including USB, near-field communication (NFC), radio-frequency identification (RFID), or Bluetooth. Some tokens have audio capabilities designed for those who are vision-impaired.
Password types
All tokens contain some secret information used to prove identity. There are four different ways in which this information can be used:
Static password token The device contains a password that is physically hidden (not visible to the possessor), but is transmitted for each authentication. This type is vulnerable to replay attacks. Synchronous dynamic password token A timer is used to rotate through various combinations produced by a cryptographic algorithm. The token and the authentication server must have synchronized clocks. Asynchronous password token A one-time password is generated without the use of a clock, either from a one-time pad or cryptographic algorithm. Challenge–response token Using public key cryptography, it is possible to prove possession of a private key without revealing that key. The authentication server encrypts a challenge (typically a random number, or at least data with some random parts) with a public key; the device proves it possesses a copy of the matching private key by providing the decrypted challenge. Time-synchronized, one-time passwords change constantly at a set time interval; e.g., once per minute. To do this, some sort of synchronization must exist between the client's token and the authentication server. For disconnected tokens, this time-synchronization is done before the token is distributed to the client. Other token types do the synchronization when the token is inserted into an input device. The main problem with time-synchronized tokens is that they can, over time, become unsynchronized. However, some such systems, such as RSA's SecurID, allow the user to re-synchronize the server with the token, sometimes by entering several consecutive passcodes. Most also cannot have replaceable batteries and only last up to 5 years before having to be replaced – so there is an additional cost. Another type of one-time password uses a complex mathematical algorithm, such as a hash chain, to generate a series of one-time passwords from a secret shared key. Each password is unique, even when previous passwords are known. The open-source OATH algorithm is standardized; other algorithms are covered by US patents. Each password is observably unpredictable and independent of previous ones, whereby an adversary would be unable to guess what the next password may be, even with knowledge of all previous passwords.
Physical types
Tokens can contain chips with functions varying from very simple to very complex, including multiple authentication methods. The simplest security tokens do not need any connection to a computer. The tokens have a physical display; the authenticating user simply enters the displayed number to log in. Other tokens connect to the computer using wireless techniques, such as Bluetooth. These tokens transfer a key sequence to the local client or to a nearby access point. Alternatively, another form of token that has been widely available for many years is a mobile device which communicates using an out-of-band channel (like voice, SMS, or USSD). Still other tokens plug into the computer and may require a PIN. Depending on the type of the token, the computer OS will then either read the key from the token and perform a cryptographic operation on it, or ask the token's firmware to perform this operation. A related application is the hardware dongle required by some computer programs to prove ownership of the software. The dongle is placed in an input device and the software accesses the I/O device in question to authorize the use of the software in question. Commercial solutions are provided by a variety of vendors, each with their own proprietary (and often patented) implementation of variously used security features. Token designs meeting certain security standards are certified in the United States as compliant with FIPS 140, a federal security standard. Tokens without any kind of certification are sometimes viewed as suspect, as they often do not meet accepted government or industry security standards, have not been put through rigorous testing, and likely cannot provide the same level of cryptographic security as token solutions which have had their designs independently audited by third-party agencies.
Disconnected tokens
Disconnected tokens have neither a physical nor logical connection to the client computer. They typically do not require a special input device, and instead use a built-in screen to display the generated authentication data, which the user enters manually themselves via a keyboard or keypad. Disconnected tokens are the most common type of security token used (usually in combination with a password) in two-factor authentication for online identification.
… excerpt ends here. Continue reading the full article.
