5 ms·

> why not just send the actual message via that mechanism? suppose you can transmit information securely only for some time. Exchange one time pads ahead of ti

by cuu508 13y ago

> why not just send the actual message via that mechanism? suppose you can transmit information securely only for some time. Exchange one time pads ahead of time, and use them later to communicate over insecure channel

andrewla 13y ago
By assumption, the only way to "transmit information securely" is by one-time pads. So...
- dllthomas 13y ago
  That was not the assumption. The assumption (or assertion) was that one-time pads were the only unbreakable encryption. There are ways of securing things other than encryption (most obviously physical isolation).
  - andrewla 13y ago
    Ach! I let myself get drawn into a semantic argument, and it earned me my first downvotes! My only point was that talking about one-time-pads as "unbreakable" encryption is not a useful discussion, since "unbreakable" and "encryption" need to be better defined. If we expand the definition of "encryption scheme" sufficiently to allow transmission of secrets outside of cryptographic channels, then OTP is not even close to the only unbreakable system. Only by explicitly defining attack vectors can we really get a good framework for reasoning about cryptography, and even then we know that we can prove an encryption technique is bad. For "goodness", all we can do is increase our confidence, until the day the confidence drops to 0. Anyway, with this last salvo, I'll retreat from this conversation; it's pretty clear to me that my inane ramblings about semantics are as annoying to the community here as they are to me when other people make them.
    - hueving 13y ago
      >My only point was that talking about one-time-pads as "unbreakable" encryption is not a useful discussion, since "unbreakable" and "encryption" need to be better defined. No they don't. You are receiving negative feedback because you are trying to adjust definitions that have been well-defined by the crypto community. When talking about the security of an encryption algorithm, the key distribution has absolutely nothing to do with it. Stop conflating the two. >If we expand the definition of "encryption scheme" sufficiently to allow transmission of secrets outside of cryptographic channels, then OTP is not even close to the only unbreakable system. Would you care to share with us some of these other unbreakable systems? Remember, the keys are the only thing that can be transmitted outside of the channel and they cannot be based on the information being encrypted.
    - darkmighty 13y ago
      "If we expand the definition of "encryption scheme" sufficiently to allow transmission of secrets outside of cryptographic channels, then OTP is not even close to the only unbreakable system." Any scheme which allows sharing arbitrary amounts of random information is less than or equally secure as an OTP (security defined per symbol) since OTP reveals no information per symbol; also, it uses the minimum amount shared information to do so, provided your symbols are equiprobable.
      - andrewla 13y ago
        I agree, OTP is optimal, it's just not unique, even by a very broad definition of what an OTP is. Sending a Turing machine to the other party through a secondary channel, for example, would produce an equivalently (not more) secure mechanism. Or sending a normal real number as the key, and the ciphertext is an index into the base26 expansion. Technically, either of these could be slightly more secure, in that they need not leak the length of the plaintext. For transmitting a single "yes" vs. "no" answer, that could be a fatal attack vector for a naive OTP.

by cuu508 13y ago

andrewla 13y ago

By assumption, the only way to "transmit information securely" is by one-time pads. So...

dllthomas 13y ago
That was not the assumption. The assumption (or assertion) was that one-time pads were the only unbreakable encryption. There are ways of securing things other than encryption (most obviously physical isolation).
- andrewla 13y ago
  Ach! I let myself get drawn into a semantic argument, and it earned me my first downvotes! My only point was that talking about one-time-pads as "unbreakable" encryption is not a useful discussion, since "unbreakable" and "encryption" need to be better defined. If we expand the definition of "encryption scheme" sufficiently to allow transmission of secrets outside of cryptographic channels, then OTP is not even close to the only unbreakable system. Only by explicitly defining attack vectors can we really get a good framework for reasoning about cryptography, and even then we know that we can prove an encryption technique is bad. For "goodness", all we can do is increase our confidence, until the day the confidence drops to 0. Anyway, with this last salvo, I'll retreat from this conversation; it's pretty clear to me that my inane ramblings about semantics are as annoying to the community here as they are to me when other people make them.
  - hueving 13y ago
    >My only point was that talking about one-time-pads as "unbreakable" encryption is not a useful discussion, since "unbreakable" and "encryption" need to be better defined. No they don't. You are receiving negative feedback because you are trying to adjust definitions that have been well-defined by the crypto community. When talking about the security of an encryption algorithm, the key distribution has absolutely nothing to do with it. Stop conflating the two. >If we expand the definition of "encryption scheme" sufficiently to allow transmission of secrets outside of cryptographic channels, then OTP is not even close to the only unbreakable system. Would you care to share with us some of these other unbreakable systems? Remember, the keys are the only thing that can be transmitted outside of the channel and they cannot be based on the information being encrypted.
  - darkmighty 13y ago
    "If we expand the definition of "encryption scheme" sufficiently to allow transmission of secrets outside of cryptographic channels, then OTP is not even close to the only unbreakable system." Any scheme which allows sharing arbitrary amounts of random information is less than or equally secure as an OTP (security defined per symbol) since OTP reveals no information per symbol; also, it uses the minimum amount shared information to do so, provided your symbols are equiprobable.
    - andrewla 13y ago
      I agree, OTP is optimal, it's just not unique, even by a very broad definition of what an OTP is. Sending a Turing machine to the other party through a secondary channel, for example, would produce an equivalently (not more) secure mechanism. Or sending a normal real number as the key, and the ciphertext is an index into the base26 expansion. Technically, either of these could be slightly more secure, in that they need not leak the length of the plaintext. For transmitting a single "yes" vs. "no" answer, that could be a fatal attack vector for a naive OTP.