Cryptography from A to Z

       From the bridge of the aircraft carrier Akagi, Adm. Chuichi Nagumo peered across the tranquil Pacific toward Midway Island. Three hours had passed since he launched 108 planes against the tiny atoll. A victory here, the Pearl Harbor veteran knew, would allow his fleet to advance on Hawaii and then threaten the West Coast of the United States. Midway would be Japan's passageway east.
       Even though his air strike at dawn had destroyed Midway's fuel supply and decimated the island's fighter squadrons, Nagumo was worried. One of his scouts had reported an enemy aircraft carrier 200 miles away and nearing. No carriers should be nearby, Nagumo thought. He expected no U.S. ships and little resistance. Midway was to be an easy target, like Pearl Harbor had been six months before.
       Nagumo didn't know about the codebreaking genius of the Combat Intelligence Unit, a group of three U.S. cryptanalysts in Pearl Harbor's Navy yard. They monitored all major and most minor Japanese fleet circuits and had succeeded in tunneling into the Japanese JN25b cipher and its internal time and place encoding. On May 28, 1942, six days before Nagumo aimed his Zeroes at Midway, the codebreakers handed Adm. Chester Nimitz the complete tactical plan the Japanese would use in the battle.
       On the morning of June 4, three carriers from Nimitz's Pacific fleet waited on Admiral Nagumo's flank. Still unaware of the extent of the threat to the northeast, Nagumo recalled his interceptors, which were low on gas after swarming on Midway. He decided they should land, refuel and replace their bombs with the 250 kg torpedoes that could do more damage to enemy ships. The laborious process took two hours.
       The delay proved deadly. U.S. planes attacked soon afterwards. Dive-bombers from the Enterprise and Yorktown screamed down and soon three of Nagumo's four carriers were ablaze. Nagumo would say later of the Soryu, "Fires enveloped the whole ship in no time." She was abandoned 30 minutes later. Nagumo's last carrier, Hiryu, sank the next day. Thanks to the Pearl Harbor cryptanalysts, Japan's eastward advance had been halted. The remnants of the once-proud First Air Fleet limped west in hasty retreat. An inferior U.S. force had defeated a Japanese armada. American codebreaking had turned the tide of a war.
       World War II was when cryptology, the science of reading and writing secrets, came into its own. By cracking the Nazis' Enigma machine, Allied cryptanalysts saved the world a year of war in Europe. The decoding of Japan's diplomatic ciphers lent a sorely needed edge to the Allied war efforts in the Pacific. Codebreaking also led to the United States shooting down Adm. Isoroku Yamamoto's personal airplane near Guadalcanal, a move that struck a heavy blow to Japanese morale.
       Modern wars have highlighted the military benefits of codemaking and codebreaking--together called cryptology--but ciphers and codes have existed for millennia. Julius Caesar wrote to Cicero in a cipher similar to Usenet's ROT-13 that replaced letters with the characters three places further down the alphabet. The Greeks invented a cryptographic signaling system that replaced letters with two-digit numbers from 11 to 55. Roger Bacon, an English monk who lived in the 13th century, wrote: "A man is crazy who writes a secret in any other way than one which will conceal it from the vulgar."

Modern Encryption

       For all its bewildering jargon, the concept of cryptography is straightforward: a sender wants to write a message and prevent an eavesdropper from understanding it. This can be done through encryption and encipherment, which scramble or rearrange the components of a message, or through a code in which one phrase represents another. Modern computers use ciphers.
       Ever since the ciphers of the Greeks and Romans, covert writing techniques have relied on the sender and recipient holding identical copies of a "key," usually a secret phrase that both parties must agree on before they can communicate. (The Confederates showed remarkable optimism but little prescience when choosing the phrase "COMPLETE VICTORY" as a key for Civil War ciphers.) That technique, however, limits the system's usefulness. If Alice wants to send a message to Bob and they haven't decided on a key, how can they communicate privately?
       They can't. An eavesdropper could intercept a key if Bob sent it to Alice. Until, at least, Whitfield Diffie and Martin Hellman invented public-key cryptography in 1975.
       Now Alice can send a private message to Bob, even if they've never met. In public-key cryptography, each correspondent owns a private key and a public key, which often is published in a directory. Think of the technique as creating a public mailbox; anyone can drop letters in the mailbox, but only the person with the right key can remove them. This development marked the end of special key couriers with black bags and the beginning of software like Phil Zimmermann's Pretty Good Privacy.
       Law enforcement agencies and the National Security Agency weren't exactly pleased by these advancements. They contend that crypto is dangerous in the wrong hands, which is why the Clinton administration continues to treat encryption products as though they were munitions. For export purposes, crypto is treated as a B-2 stealth bomber or an M-1 Abrams tank. An executive order, which succeeded the International Traffic in Arms Regulations (ITAR), requires firms to seek licenses to ship crypto overseas.
       The U.S. government's view stems from when encryption was largely the province of soldiers and spies. Indeed, the science of cryptology owes much of its advancement to codebreakers and codemakers who worked for governments. But the world has changed. Computers are no longer a military monopoly. Strong crypto is needed online. Public-key cryptography, besides ensuring that your messages are secure, can also identify who you're communicating with or buying from online. It provides the protocols for scrambling credit-card numbers and generating digital coins. It allows digital signatures, proofs of identity online, digital time stamps and even secure electronic voting. It lets anonymous remailers exist. It provides for secure telnet connections. Crypto provides the foundation and steel girders for an information society.

Munition or Net-Necessity?

       Encryption presents the Feds with an unwelcome dilemma: It yields hefty benefits when used to secure networks, but presents law enforcement agencies with real drawbacks when agents try in vain to read a suspect's seized e-mail.
       This schizophrenic policy betrayed itself when the Clinton administration introduced the Clipper Chip in April 1993. The White House tried to pass off the device as offering users superior encryption capabilities at the small price of ensuring continued government access to encrypted communications. The plan, crafted by the NSA, was for the government to hold master copies of keys "in escrow" until needed by law enforcement. The scheme met with savage opposition and the Clipper Chip soon sunk.
       That miserable failure hasn't prevented FBI director Louis Freeh from launching his own attacks on crypto. In alarmist speeches, he repeatedly has linked strong encryption to terrorists such as the Oklahoma City bombers. Freeh told Congress that "unbreakable encryption" will "seriously and fundamentally threaten" public safety. "The potential use of such robust encryption products by a vast array of criminals and terrorists to conceal their criminal communications and information poses an extremely serious and, in my view, unacceptable threat to public safety," he said. (Attorney General Janet Reno and Jamie Gorelick, deputy attorney general, have echoed the FBI chief, and documents that the Electronic Privacy Information Center obtained under the Freedom of Information Act demonstrate that the bureau would like to outlaw encryption that doesn't have a backdoor for the government.) Still, Freeh speaks some truth. If crypto is widespread, it will hinder the FBI's ability to wiretap. It will allow miscreants to encrypt files in a manner impervious to prosecutors' most determined attacks. It will make it more difficult for the NSA to scan international phone calls in bulk for code words that hint at illicit activity. It will hinder convictions--but then again, so do Miranda rights. To Freeh, controls on encryption are a matter of restoring the "balance" that's tilting away from law enforcement. "In a very fundamental way, conventional encryption has the effect of upsetting the delicate legal balance of the Fourth Amendment, since when a judge issues a search warrant it will be of no practical value when this type of encryption is encountered," he said.
       What Freeh neglects to mention is how the scales are already tipped in favor of the FBI. Modern communications technologies make it possible for law enforcement agents to collect an unprecedented amount of information on ordinary citizens without their knowledge. Digital technology allows governments to do a much more thorough job of monitoring an ordinary person's actions and opinions than ever before. If the Justice Department ransacks your home, you'll know it. Not so when your communications are digital and are culled from a mail server without your knowledge. Crypto restores the balance of privacy.
       "It's an effort by the government to permanently shift the power in favor of surveillance," ACLU privacy guru Don Haines says. "This occurs in a digital medium, where for the first time we can make Big Brother real. Before, the manpower required was prohibitive. Now it's digital. You set your computers to search for a particular sequence of bits."
       This view is not new. Thirty years ago, Alan Westin wrote in his book Privacy and Freedom that "the issue of privacy raised by computerization is whether the increased collection and processing of information for diverse public and private purposes, if not carefully controlled, could lead to a sweeping power of surveillance by government over individual lives and organizational activity."
       His remarks would prove prophetic.

U.S. Businesses: Out of Business?

       American businesses have launched their own offensive to support encryption. They contend that their overseas competitors aren't hindered by ITAR and are free to sell strong encryption around the globe. Execs have told Congress for years that current regulations cost U.S. industry millions. They point to RSA Data Security's decision to license its patents to NTT, a Japanese firm. They warn that European or Asian software makers may drive U.S. firms off the encryption playing field forever.
       The White House reacted swiftly to the complaints. Clinton recently appointed a crypto-ambassador to lobby foreign governments to comply with U.S. rules and move toward a global framework requiring key escrow. If successful, the move would nullify the industry's argument; after all, foreign firms would be equally hobbled. "What we need to do, very clearly, is to spend a lot of time with other countries," says William Reinsch, Commerce Department undersecretary for export administration.
       The debate grew even hotter when Sen. Conrad Burns (R-Montana) introduced a bill last spring that would lift export controls. With White House arm-twisting--some reports say Clinton himself worked the phones--and adept lobbying by the Justice Department, the legislation perished. Sen. Jim Exon (D-Nebraska), proud sponsor of the Communications Decency Act, personally dealt the death blow by blocking the proposal from leaving the Commerce Committee. Burns plans to reintroduce "Pro- CODE" legislation this year.
       The other way to skirt the export embargo is through the courts. The Electronic Frontier Foundation scored an early victory in its legal attack on the regulations last December when a Federal judge in San Francisco ruled that ITAR was unconstitutional. Another case is moving through the D.C. Federal appeals court, which heard oral arguments last month. Clinton responded to these legislative and judicial attacks by signing an executive order on Nov. 15, 1996 that he billed as a "compromise," but in truth it only transferred jurisdiction over encryption exports from the State Department to the Commerce Department. The regulations remain almost entirely the same. Clinton wrote at the time, almost parroting Freeh, that "encryption products, when used outside the United States, can jeopardize our foreign policy and national security interests...The exportation of encryption products accordingly must be controlled to further U.S. foreign policy objectives, and promote our national security, including the protection of the safety of U.S. citizens abroad." Attached to Clinton's executive order was another reason for privacy advocates to cry foul: a "key recovery" proposal. It's Clipper with a twist, a divide-and-conquer strategy designed to splinter an industry previously united in opposition. It slightly relaxed rules on exporting crypto only for those businesses that pledge to devise a key escrow system ensuring government access to keys. That presents Silicon Valley companies with a kind of unholy prisoner's dilemma--if you don't buy into this plan, your competitor will. Faced with the prospect of hanging together or hanging separately, some hardware manufacturers already have signed up.

Security through Complex Mathematics

       Ironically, the Federal government may have done more than anyone else to further the spread of encryption. In 1975, it unveiled the Data Encryption Standard (DES), arguably still the world's most popular data-scrambling algorithm. It proved reasonably fast and apparently secure, even after the National Security Agency weakened the final version. However, the NSA had made a crucial mistake: they believed the National Institute of Standards and Technology would publish specifications only for a hardware version of DES.
       Instead, enough information appeared in the Federal Register to allow programmers to write DES applications. Soon, they became widely available, bringing reasonable digital privacy to anyone with a personal computer. The explosion of personal computers allowed more people to encrypt files with DES than the NSA ever imagined. Chastened officials say privately that, from the standpoint of national security, DES was the worst mistake the NSA ever made.
       The debate over what encryption products can be exported revolves around the strength of the application's key; longer keys are more difficult for an attacker to break. The Commerce Department permits firms to export 40-bit DES, or 56-bit DES with a pledge to develop "key recovery" products.
       Symmetric algorithms like DES use keys often ranging from 40 bits to 128 bits, with an 8-bit key having 28--or 256--possible values. Guessing that key takes 256 attempts, with a 50 percent chance of finding the correct key after 128 tries. Beware short key lengths: an attacker with custom hardware can crack a 40-bit DES key in milliseconds and a 56-bit key in just minutes. But a 128-bit key requires an adversary to wait perhaps 1017 years--or longer than the known age of the universe! No wonder the NSA is lamenting. (Public-key cryptosystems like PGP calculate the security of key lengths differently. A 128-bit PGP key is woefully inadequate; a 1024-bit PGP key is reasonably safe.)


       The debate swirling through Capitol Hill conference rooms and the corridors of the White House revolves around one basic question: What role should the government play in regulating encryption?
       The founding fathers might be startled by the Byzantine rules. After all, some revolutionaries were cryptographers themselves. Benjamin Franklin in 1781 crafted a substitution cipher based on a 682-character French phrase. James Madison created a code replacing words with two- and three-digit numbers that he used until 1793.
       But by far the most remarkable cryptologist of the Revolutionary War was the author of the Declaration of Independence, Thomas Jefferson, who between 1790 and 1800 invented a cipher system so far ahead of its time that it remained in use even into the late 20th century.
       He called it his "wheel cypher." One design consisted of a six-inch rod with 36 wheels on it, each with an alphabet scrambled in a different order. The wheels can be rearranged for different correspondents for a total of 36 factorial, or 37 x 1040 possible combinations.
       In The Codebreakers, historian David Kahn writes: "Jefferson's wheel cypher was far and away the most advanced devised in his day...Had the President recommended his own system to Secretary of State James Madison, he would have endowed his country with a method of secret communication that would almost certainly have withstood any cryptanalytic attack of those days. Instead he appears to have filed andforgotten it."
       To Jefferson, the will and welfare of the people--not federal bureaucrats--were the prop and purpose of government. His deepest trust lay in the wisdom of citizens to use freedom wisely and in a belief that the essence of democracy was a central government limited in power. Perhaps, when contemplating encryption regulations, Bill Clinton could learn something from his renowned predecessor.

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