Understanding FIPS Authentication Methods

Username and Password Authentication over the Console and SSH

In this authentication method, the user is requested to enter the username and password. The device enforces the user to enter a minimum of 10 characters password that is chosen from the 96 human-readable ASCII characters.

In this method, the device enforces a timed access mechanism—for example, first two failed attempts to enter the correct password (assuming 0 time to process), no timed access is enforced. When the user enters the password for the third time, the module enforces a 5 second delay. Each failed attempt thereafter results in an additional 5 second delay above the previous failed attempt. For example, if the fourth failed attempt is a 10 second delay, then the fifth failed attempt is a 15 second delay, the sixth failed attempt is a 20 second delay, and the seventh failed attempt is a 25 second delay.

Therefore, this leads to a maximum of seven possible attempts in a 1 minute period for each getty active terminal. So, the best approach for the attacker would be to disconnect after 4 failed attempts, and wait for a new getty to be spawned. This would allow the attacker to perform roughly 9.6 attempts per minute (576 attempts per hour or 60 minutes). This would be rounded off to 9 attempts per minute, because there is no such thing as 0.6 attempts. Thus the probability of a successful random attempt is 1/9610, which is less than 1/1 million. The probability of a success with multiple consecutive attempts in a 1 minute period is 9/(9610), which is less than 1/100,000.

Username and Public Key Authentication over SSH

In SSH public key authentication, you provide the username and validate the ownership of the private key corresponding to the public key stored on the server. The device supports ECDSA (P-256, P-384, and P-521) and RSA (2048, 3072, and 4092 modulus bit length) key-types. The probability of a success with multiple consecutive attempts in a 1-minute period is 5.6e7/(2128).