True Names and the Opening of the Cyberspace Frontier by Vernor Vinge Read Free Book Online

it is much easier to encrypt with very large keys than it is to break a message (decrypt by brute force, without the secret key). The difference in effort widens exponentially with increasing key size. Advances in computer power are more than offset by the ability to use longer keys. Likewise, “massively parallel computers,” often cited by the ignorant as a possible way to break these ciphers, offer only marginal, linear speedups on brute-force cracking … utterly inconsequential compared with the efforts needed to factor large numbers. Faster computers are a big win for strong cryptography.
    The important distinction between modern cryptography and conventional, or classical, cryptography is that the keys are asymmetric in modern cryptography, whereas in classical cryptography the parties to a cipher had somehow to exchange the same key. Exchanging keys with hundreds or even thousands of correspondents is much harder than simply looking up a key in a public-key directory, or asking for it to be sent in e-mail. More important for our purposes here, only the public-key approach allows the uses described here. For example, digital signatures rely on keeping the secret key a secret. If conventional ciphers were used, then anyone sharing one’s private key could forge signatures, withdraw money, and generally wreak havoc. (Digital signatures exploit this asymmetry property of keys by allowing anyone to easily authenticate a signature without having access to the key that would allow forgery of a signature.)
    Appropriately for this book, encryption is like an unbreakable “force field” around an encrypted item, much like the “bobbles” described in Vinge’s The Peace War. The amount of energy required to run the computers—not to mention the number of such computers and the time involved!—can be shown to be greater than all of the energy all of the stars in the universe will ever produce. This for a sufficiently large key, one with an RSA modulus of a few thousand digits. (This has not yet been mathematically proved, in that factoring large numbers has not been proved to be “hard.” It is remotely possible that some fast factoring breakthrough will be discovered, but this is considered by nearly all mathematicians to be extremely unlikely. The speculation that the NSA knows how to quickly factor large numbers, and thus break RSA, seems equally unlikely.)
    The Encryption Controversy
    Governments are clearly afraid of strong cryptography in the hands of the citizenry. Governments around the world have attempted to deal with the implications of this threat by limiting the size of keys that citizens may use, by limiting the types of algorithms that may be used, by demanding that citizen-units “escrow” (deposit) their keys with the government or with registered government agents, and by banning strong cryptography altogether. This is a battle over whether one’s thoughts and messages may be placed inside sealed envelopes or must be written on “postcards,” for the government to read, as Phil Zimmermann points out. One U.S. government proposal, repeated in several variants, is that messages may be sealed in envelopes, but only if the government has a special key to open them. This is like allowing citizens to have curtains on windows, but only if the local police can trigger a special transparency mode. And the issues are quite comparable. Encryption, as we will see, makes certain kinds of crimes and revolutionary activities much more feasible, but so do locked doors, curtains, and whispered conversations. And yet we would not consider outlawing locked doors, curtains, and whispered conversations. As Zimmermann notes, “I should be able to whisper in your ear, even if you’re a thousand miles away,” referring of course to e-mail or to voice-scrambling technology (public-key cryptography is fast enough, when combined cleverly with conventional