UNBREAKABLE CODE
    
              By Roger Rapoport
    
    Urere you the sort of kid who loved to fiddle with a
    secret~ode ring? Do you send messages that you
    wouldn't want business competitors to intercept?
    Perhaps you cringe at the thought of a tax audit. If
    so, you're going to love this.
    
    For years now it's seemed that the Silicon
    Revolution would leave us all naked to the world.
    Anyone with enough nosiness, gall, and the price of
    a big computer can build an electronic data base
    that contains more information about us than we
    can remember ourselves. The insurance industry
    has done it. So have the credit bureaus. Some
    government agencies do little else.
    
    Now the computers that helped rob us of our
    privacy are giving it backÄwith interest. Two
    cryptographic geniuses have made the break-
    through that code builders have dre~ned of for cen-
    tunes: They've invented a practical code that can't
    be broken. Once you've coded your information,
    no oneÄnot the CIA, not the NSA, not even the
    IRSÄcan figure it out unless you've told them how.
    With the right programming, most hame computers
    could code and decode messages. But without the
    key, even IBM's biggest number crunchers could
    work far ~nto the next century without unscram-
    bling them.
    
    It's enough to make professional snoops weep. In
    fact, they've spoken out publicly against nongov-
    ernmental code research, interfered with patent ap-
    plications, and even threatened un~versity-based
    cryptographers with prosecution under the State
    Department's International Traffic in Arms regula-
    tion. Now the Defense Department is seeking the
    power to review articles on cryptography and to ban
    publication of any that it considers too ~nformative.
    
    This round in the battle between privacy freaks
    and code breakers got started when Martin Hell-
    man, a thirty-three-year-old Stanford University
    professor of electrical engineering, linked up with
    another code junkie, Whitfield Oiffie. Schooled in
    symbolic mathematical manipulations at MIT's
    Artificial Intelligence Laboratory, Diff~e had left an
    industry job in California to search informally for
    the perfect code. After studying the classical litera-
    ture, he camped his way across the country, visiting
    all the major centers of cryptographic research.
    Each night he examined the latest technical papers
    from university and corporate labs by firelight.
    
    At IBM's Yorlctown Heights, New York, lab, a
    scientist suggested that he look Hellman up back in
    California. "When I arnved in Palo Alto," Difhe
    
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    recalls, "I called Hellman, and we each immediately
    found the other to be the most informed person in
    this field not governed by federal security regula-
    tions."
    
    The problem they were trying to solve is lodged
    deep in modern code practices. Most coded
    messages these days are sent from one computer to
    another over telephone lines. For confirmation,
    they are also sent by couner. But that doesn't come
    cheap, and it often means delays when long dis-
    tances are inYolved. A computer-wise thief who's
    wormed his way into a bank's message network can
    vanish with millions of dollars before anyone
    realizes that his orders to transfer the money
    weren't authorized. Worse yet for government
    cryptographers, there's always a chance that the
    courier will be intercepted or will defect with the
    message.
    
    Then there are the electronic eavesdroppers. The
    National Security Agency has computers tied into
    long~istance telephone links all over the world.
    The moment a phrase suggesting a topic that in-
    terests the agency appears in a conversation, the
    NSA's tape recorders kick in. Similar equipment
    monitors data-processing lines here and abroad.
    Anytime someone makes a call or sends a wire, the
    NSA can listen in. New equipment will soon enable
    the a~encY to read mail. even before it's sent bY
    
    . . . . . . . . .
    
    catchlng ano mterpretlng an electnc typewrlter s
    vibrations with remote sensing equipment. And Yir-
    tually anything the NSA can record, the agency's
    computers can decode.
    
    Hellman and Diffie concluded that the majar ob-
    stac]e to secure trans~rnss~on of data over telepro-
    cessing networks lay in distributing the key, the in-
    structions that tell the recipient how to decipher a
    message. "Traditionally," Hellman explains,
    '`keys have been moved by couriers or registered
    mail. But ~n an age of instant communic~tions it
    was unrealistic for computer manufacturers to ex-
    pect customers to wait days for the code to arrive.
    What was needed was a system immediately access-
    ~ble to users who may never have had pnor contact
    with each other."
    
    The idea of sending coded messages to total
    strangers seemed impractical at first. "In the past,"
    Diffle says, "cryptography operated on a strongbox
    approach. The sender uses one key to lock up his
    message, and the recipient has a matching key that
    unlocks the meaning. As Hellman and I talked, we
    became intrigued by the idea of a system that used
    two different keys~ne for enciphering and a sec-
    ond for decIphering. This method would operate
    like a twenty-four-hour bank teller. Any depositor
    can open the machine to put his money in, but only
    the bank has the combination to unlock the safe."
    
    For a long time now messages have been trans-
    lated into high-security codes by converting the