Following are some specific cryptography guidelines to consider when designing and implementing a solution for transmission confidentiality:
■ Cryptography can become a performance bottleneck, and careful analysis is required to determine where data should be protected. In general, if confidential or sensitive data travels over a network where an attacker could easily intercept communications (such as a network outside of the organization's physical control or a network where device compromises are likely), communications must be protected as the security policy defines.
■ Modern cryptography algorithms can now be exported, although some might still be subject to controls, depending on legal regulations. Use the strongest available cryptography to provide sufficient protection. Be cautious, however; some cryptographic algorithms allow you to specify extremely long key lengths, which, at some point, do not provide worthwhile confidentiality improvements over shorter keys.
■ Use only well-known cryptographic algorithms, because only well-known algorithms that have been tested and analyzed are considered trustworthy. Examples of well-known algorithms are Triple Data Encryption Standard (3DES), Advanced Encryption Standard (AES), and Rivest Cipher 4 (RC4). In general, do not trust any algorithms that claim to represent a security breakthrough; these are often extremely weak and easily broken.
NOTE The data encryption standard (DES) uses a 56-bit key. 3DES encrypts the data three times, with up to three different keys.
■ Do not forget that encryption provides only confidentiality, and most organizations consider data integrity and authenticity equally important security elements. If possible, use both confidentiality- and integrity-guaranteeing cryptographic algorithms.
For example, to lower communication costs, a health insurance company decides to connect some of its branch offices to its headquarters over the Internet. The company must protect patient record confidentiality; because attackers on the Internet can intercept communications, the company implements a VPN using the strongest possible encryption algorithms to guarantee data confidentiality. In the event of interception, it is unlikely that the attacker can decrypt messages that are protected with modern cryptographic algorithms such as 3DES, AES, or RC4.
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