Asoftware token (a.k.a.soft token) is a piece of atwo-factor authentication security device that may be used to authorize the use of computer services.[1] Software tokens are stored on a general-purpose electronic device such as adesktop computer,laptop,PDA, ormobile phone and can be duplicated. (Contrasthardware tokens, where the credentials are stored on a dedicated hardware device and therefore cannot be duplicated — absent physical invasion of the device)
Because software tokens are something one does not physically possess, they are exposed to unique threats based on duplication of the underlying cryptographic material - for example,computer viruses andsoftware attacks. Both hardware and software tokens are vulnerable to bot-basedman-in-the-middle attacks, or to simplephishing attacks in which theone-time password provided by the token is solicited, and then supplied to the genuine website in a timely manner. Software tokens do have benefits: there is no physical token to carry, they do not containbatteries that will run out, and they are cheaper than hardware tokens.[2]
There are two primary architectures for software tokens:shared secret andpublic-key cryptography.
For a shared secret, anadministrator will typically generate aconfiguration file for each end-user. The file will contain a username, apersonal identification number, and thesecret. This configuration file is given to the user.
The shared secret architecture is potentially vulnerable in a number of areas. The configuration file can be compromised if it is stolen and the token is copied. With time-based software tokens, it is possible to borrow an individual'sPDA or laptop, set the clock forward, and generate codes that will be valid in the future. Any software token that uses shared secrets and stores the PIN alongside the shared secret in a software client can be stolen and subjected to offline attacks. Shared secret tokens can be difficult to distribute, since each token is essentially a different piece of software. Each user must receive a copy of the secret, which can create time constraints.
Some newer software tokens rely onpublic-key cryptography, or asymmetric cryptography. Thisarchitecture eliminates some of the traditional weaknesses of software tokens, but does not affect their primary weakness (ability to duplicate). A PIN can be stored on a remote authenticationserver instead of with the token client, making a stolen software token no good unless the PIN is known as well. However, in the case of a virus infection, the cryptographic material can be duplicated and then the PIN can be captured (via keylogging or similar) the next time the user authenticates. If there are attempts made to guess the PIN, it can be detected and logged on the authentication server, which can disable the token. Using asymmetric cryptography also simplifies implementation, since the token client can generate its own key pair and exchange public keys with the server.