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582 Chapter 10 • Public Key Infrastructure

the physical access security on machines carrying sensitive certificates;
even the use of radio identifiers so as to lock a workstation when its user
is away from it for more than a few seconds.

It is generally accepted that software storage is not a reliable means of storing
high-security private keys.To overcome the issues of software storage, Hardware
Storage Modules (HSMs) were created. HSMs, such as Smart Cards, Personal
Computer Memory Card International Association (PCMCIA) cards, and other
hardware devices, store private keys and handle all encryption and decryption of
messages so that the key does not have to be transmitted to the computer. (Using
magnetic media is really the equivalent of software key storage with an offline file
store, and should not be thought of as hardware storage of keys.) Keeping the keys
off of the computer prevents information about the keys from being discovered in
computer memory.
Smart Cards are the most flexible method of storing personal private keys using
the hardware storage method. Since Smart Cards are normally about the size of a
credit card, they are easily stored and can resist a high level of physical stress. Smart
Cards are also not very expensive. Unlike a credit card that has a magnetic strip,
Smart Cards store information using microprocessors, memory, and contact pads for
passing information (see Figure 10.10).

Figure 10.10 A DSS Smart Card

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