Obsenity is NOT protected under the first amendment.
This is absolutely true. However, "obscenity" in this context is a very precise legal term, and does not apply to all pornography. I forget the exact Supreme Court case, but for material to be legally obscene, it must meet a three-fold test:
It must appeal to the "purient interest" (i.e., be sexual in nature),
It must contain no redeeming value-- scientifically, socially, literary, or as a work of art, and
It must violate community standards. In other words, what is legally obscene changes from location to location. The Supreme Court never even suggested a blanket definition of obscenity.
Also, certain types of pornography are always obscene: that which involves animals, children, or the dead. (The idea is that none of these objects/people/things can give consent.)
Of course, the rules are different and weaker when children are involved. Some pornographic material, although not obscene by local community standards, might still be judged harmful to minors. But this still reinforces my point-- laws regarding obscenity have very little bearing to the current debate.
(Disclaimer: I am not a lawyer, and invite any lawyers out there to correct/clarify what I have said here.)
Caveat: We are now outside my area of expertise. If anyone knows more about these matters, please feel free to correct my mistakes.
My reply would be that quantum computers are not non-deterministic. A non-deterministic machine is one that is allowed to make guesses, or choose between multiple possibilities. To say that a non-deterministic machine can solve something in polynomial time usually includes the unspoken assumption that the machine _always guesses correctly_. So, yes, secret key encryption is probably breakable by a non-deterministic machine in linear time-- the machine simply guesses each bit of the key correctly. However, I don't think anyone has actually built a non-deterministic machine.
A quantum computer, on the other hand, can be in multiple states simultaneously-- until you look at it. When you look at it, however, it collapses into one of its component states RANDOMLY. For example, suppose you have a quantum bit ("qubit"). This bit can be in either of the two classical states: |1>, or |0>. It can also be in any combination of the two, such as (a * |1> + b * |0>). (The coefficents a and b, by the way, can be complex numbers.) When you look at the bit, on the other hand, it will collapse into one of the two classical states randomly, with the probabilites given by the values of a and b.
So, as opposed to a non-deterministic machine, a quantum machine can look at all options simultaneously but will only show you one outcome. It may not be the outcome you want, and once you look at it _all the other outcomes are gone_. The trick of quantum computing is to cleverly massage the values of a and b until you can be sure that it will collapse into an outcome you want. (This is the essence of Shor's algorithm.)
If you want to know more, look at http://www.qubit.org.
Quantum computing-- not the end of the world
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RSA slightly broken
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The situtation is both worse and better than this. If quantum computing could only be used to factor large numbers, the world wouldn't change much. We would stop using RSA encryption (which is only as secure as factoring is hard) and start using schemes based on the difficulty of the discrete log (such as El Gamal). However, Shor's algorithm can also be used to perform discrete logarithms in polynomial time, thus blowing away most of the remaining public-key algorithms and some very important key exchange schemes (particularly Diffie-Hellman). We might still be able to salvage some sort of public key scheme out of lesser known problems (like the knapsack problem), but it would take a lot of work.
So how is the situation _better_ than this? First, these advances only apply to public-key encryption, not secret-key encryption schemes like DES. Second, quantum mechanics also opens up new possibilites for key exchange that were not available before. In particular, quantum mechanics can be used to distribute random key material for a one-time pad over a public medium. There's a good overview of the process in the Oct. 1992 Scientific American, but the main idea is this: Quantum entities (photon, electrons, fundemental particles) change when observed. Therefore, someone can send out the random key material in the form of a stream of photons, and the reciever can tell if they were observed in transit.
This is a Good Thing, cryptographically speaking, because one-time pads are proven to be _unbreakable_. Furthermore, this type of key exchange has already been one, over distances as long as 30km (I believe).
So quantum computing would change things, certainly, but it's not the end of the world.
(For those interested, Schneier's _Applied Cryptography_ and the _Handbook of Applied Cryptography_ by Menzes, van Oorschot and Vanstone are good general references. As mentioned above, the quantum key distribution method can be found in Scientific American, Oct. 1992. Peter Shor's home page is here. There's lots of information on quantum computing on the web, but a good place to start is here.)
Slashdot Mirror
This is absolutely true. However, "obscenity" in this context is a very precise legal term, and does not apply to all pornography. I forget the exact Supreme Court case, but for material to be legally obscene, it must meet a three-fold test:
- It must appeal to the "purient interest" (i.e., be sexual in nature),
- It must contain no redeeming value-- scientifically, socially, literary, or as a work of art, and
- It must violate community standards. In other words, what is legally obscene changes from location to location. The Supreme Court never even suggested a blanket definition of obscenity.
Also, certain types of pornography are always obscene: that which involves animals, children, or the dead. (The idea is that none of these objects/people/things can give consent.)Of course, the rules are different and weaker when children are involved. Some pornographic material, although not obscene by local community standards, might still be judged harmful to minors. But this still reinforces my point-- laws regarding obscenity have very little bearing to the current debate.
(Disclaimer: I am not a lawyer, and invite any lawyers out there to correct/clarify what I have said here.)
Caveat: We are now outside my area of expertise. If anyone knows more about these matters, please feel free to correct my mistakes.
My reply would be that quantum computers are not non-deterministic. A non-deterministic machine is one that is allowed to make guesses, or choose between multiple possibilities. To say that a non-deterministic machine can solve something in polynomial time usually includes the unspoken assumption that the machine _always guesses correctly_. So, yes, secret key encryption is probably breakable by a non-deterministic machine in linear time-- the machine simply guesses each bit of the key correctly. However, I don't think anyone has actually built a non-deterministic machine.
A quantum computer, on the other hand, can be in multiple states simultaneously-- until you look at it. When you look at it, however, it collapses into one of its component states RANDOMLY. For example, suppose you have a quantum bit ("qubit"). This bit can be in either of the two classical states: |1>, or |0>. It can also be in any combination of the two, such as (a * |1> + b * |0>). (The coefficents a and b, by the way, can be complex numbers.) When you look at the bit, on the other hand, it will collapse into one of the two classical states randomly, with the probabilites given by the values of a and b.
So, as opposed to a non-deterministic machine, a quantum machine can look at all options simultaneously but will only show you one outcome. It may not be the outcome you want, and once you look at it _all the other outcomes are gone_. The trick of quantum computing is to cleverly massage the values of a and b until you can be sure that it will collapse into an outcome you want. (This is the essence of Shor's algorithm.)
If you want to know more, look at http://www.qubit.org.
So how is the situation _better_ than this? First, these advances only apply to public-key encryption, not secret-key encryption schemes like DES. Second, quantum mechanics also opens up new possibilites for key exchange that were not available before. In particular, quantum mechanics can be used to distribute random key material for a one-time pad over a public medium. There's a good overview of the process in the Oct. 1992 Scientific American, but the main idea is this: Quantum entities (photon, electrons, fundemental particles) change when observed. Therefore, someone can send out the random key material in the form of a stream of photons, and the reciever can tell if they were observed in transit.
This is a Good Thing, cryptographically speaking, because one-time pads are proven to be _unbreakable_. Furthermore, this type of key exchange has already been one, over distances as long as 30km (I believe).
So quantum computing would change things, certainly, but it's not the end of the world.
(For those interested, Schneier's _Applied Cryptography_ and the _Handbook of Applied Cryptography_ by Menzes, van Oorschot and Vanstone are good general references. As mentioned above, the quantum key distribution method can be found in Scientific American, Oct. 1992. Peter Shor's home page is here. There's lots of information on quantum computing on the web, but a good place to start is here.)