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Is quantum computing relevant to symmetric encryption like OTP? GP was talking about asymmetric encryption. My limited understanding is that quantum computing i

Is quantum computing relevant to symmetric encryption like OTP? GP was talking about asymmetric encryption. My limited understanding is that quantum computing is a threat to asymmetric encryption. There's also the question of, if you can distribute a key which is at least the same size as your message over a secure channel - why not just distribute your message over that channel in the first place?

karmanyaahm 3y ago
> why not just distribute your message over that channel in the first place Latency? You can hand deliver a password ahead of time, but not messages.
- ianburrell 3y ago
  One-time pad isn't a password. It is a flash drive or hard drive full of random bits.
  - InitialLastName 3y ago
    The difference between those is just one of scale and storage. You still have to reliably move a chunk of out-of-band information in a way such that it gets to (and only gets to) the person you want to have it.
    - ianburrell 3y ago
      The difference between one-time pad and stream cipher is provable, absolute secrecy, and really good secrecy. If don't care about that, there is zero point to one-time pad. Also, it isn't just a "chunk", for one-time pad it has to be the same length as the messages. Which is fine if just short messages but a lot harder if lots of data. If can exchange lots of data, better off using them as keys for stream cipher.
aetherson 3y ago
One-time pads are obviously not a serious widespread cryptography proposal. But the question of, "Why not just send the message instead of the pad" is pretty straightforward: when you have the opportunity to safely deliver the pad, you don't know what the message will be. When you do know what the message will be, you don't have the opportunity to safely deliver the pad.
hgomersall 3y ago
Because with QKD you can distribute a random key knowing that there were no observers but you cannot distribute a message with the same guarantees. Specifically, any given bit exchanged might be observed, but that is detectable so the bit can be discarded. I read some years ago about a non quantum technique to achieve the same based on (I think) noise in a coupled electronic system. I wonder if that has been tested further.

karmanyaahm 3y ago

> why not just distribute your message over that channel in the first place Latency? You can hand deliver a password ahead of time, but not messages.

ianburrell 3y ago
One-time pad isn't a password. It is a flash drive or hard drive full of random bits.
- InitialLastName 3y ago
  The difference between those is just one of scale and storage. You still have to reliably move a chunk of out-of-band information in a way such that it gets to (and only gets to) the person you want to have it.
  - ianburrell 3y ago
    The difference between one-time pad and stream cipher is provable, absolute secrecy, and really good secrecy. If don't care about that, there is zero point to one-time pad. Also, it isn't just a "chunk", for one-time pad it has to be the same length as the messages. Which is fine if just short messages but a lot harder if lots of data. If can exchange lots of data, better off using them as keys for stream cipher.

aetherson 3y ago

One-time pads are obviously not a serious widespread cryptography proposal. But the question of, "Why not just send the message instead of the pad" is pretty straightforward: when you have the opportunity to safely deliver the pad, you don't know what the message will be. When you do know what the message will be, you don't have the opportunity to safely deliver the pad.

hgomersall 3y ago

Because with QKD you can distribute a random key knowing that there were no observers but you cannot distribute a message with the same guarantees. Specifically, any given bit exchanged might be observed, but that is detectable so the bit can be discarded. I read some years ago about a non quantum technique to achieve the same based on (I think) noise in a coupled electronic system. I wonder if that has been tested further.