Data Encryption Standard (DES)

Highly sensitive digital information is often the target of computer hackers, international spies, and criminals. In order to protect such information, in 1977 the National Security Agency (NSA) and the National Bureau of Standards (NBS) adopted the Data Encryption Standard (DES) to protect sensitive, unclassified, non-military digital information from unauthorized access. Encryption is the intentional scrambling or masking of digital data to protect it from compromise.

DES utilized symmetric-key (or private-key) encryption, in which the sender and receiver of a message share a single, common key that is used to encrypt and decrypt the message. The key is a string of digits that has been generated by a complex mathematical algorithm, or formula. Private-key encryption differs from public-key encryption, which utilizes two keys—a public key to encrypt messages and a private key to decrypt them. Private-key systems are simpler and faster, but their main drawback is that both parties must somehow exchange the key in a secure manner. Public-key encryption avoids this problem because the public key can be distributed in a non-secure way, and the private key is never transmitted. In the former case, secrecy is shared between only two users, whereas in the latter, the public key is a more or less an "open secret." Thus, public-key encryption requires many more bits to rival private-key systems' level of protection.

Though the NSA usually supervises development of governmental encryption systems, its hesitation over creating such a system for public use led to an open call for the system's design. Ultimately IBM produced a 56-bit key algorithm that became DES. Controversy arose over the extent to which DES-encrypted products could be exported outside the United States, since federal regulations govern export of encrypted items. Security considerations led the U.S. government to limit the export of encryption systems to those of 40 bits or less. Since DES employed 56 bits, most products incorporating DES could not be exported, despite a report on national encryption policy issued by the National Research Council in 1996 that called for a relaxation of export regulations.

DES underwent its most serious challenge in 1998, and failed. The Electronic Frontier Foundation constructed a custom-designed machine, which broke open a DES-encrypted code in 56 hours. Subsequent tests, conducted on 100,000 PCs networked with the EFF machine, reduced the time required to 22 hours. This procedure resulted in the lifting of the U.S. restrictions on exporting DES-encrypted products.

DES's efficacy under continuous surveillance and was reassessed every five years after its inception. The 1998 EFF crack-through concluded that DES' Achilles heel was its short key length. It was recommended that DES should be replaced by Triple DES, a modified version employing 112- or 168-bit keys. DES's versatility also was limited because it worked only in hardware, and the explosion of the Internet and e-commerce led to much greater use and versatility of software than could have been anticipated by DES's designers.

As DES's vulnerabilities became apparent, the National Institute of Standards and Technology (NIST) opened an international competition in 1997 to find a permanent replacement for DES. To be christened the Advanced Encryption Standard (AES), the replacement would be operable into the 21st century. NIST recommended a minimum key length of 128 bits, and sought to guarantee that encrypted files would continue to be secure even after AES was eventually phased out. In addition, the algorithm had to implement public-key cryptography and work with key sizes of 128, 192, and 256 bits. Flexibility also was a premium concern of AES' designers. AES had to function with eight-bit processors, smart cards, ATM networks, high-definition TVs, voice-recognition systems, and satellite communications. Finally, it had to be available internationally on a non-exclusive, royalty-free basis.

Ultimately, DES was testament to the pace of technological change in the late 20th century. It was considered to be adequately powerful and impenetrable in its day. However, the cracks in DES widened into gaping holes as cryptographic and computer technology developed, and as the Internet and other networked systems heightened the need for flexible and durable encryption.