3 ms·

You would need to clone the device, as the possible challenges are infinite as they are mathematically-generated. The scheme would just be a glorified one time

You would need to clone the device, as the possible challenges are infinite as they are mathematically-generated. The scheme would just be a glorified one time pad otherwise.

leereeves 11y ago
But what can be done with the challenges that uses the "infinite" set of possible challenges instead of a finite subset that has been stored on another device? In other words, if a fake responds with anything it wants for challenges that aren't stored on the other device (the challenger), how would the challenger know the response didn't match what the real PUF would send?
- vinceguidry 11y ago
  The responses are verified mathematically in a manner akin to a hash function. It's hard to know what the PUF will send, but easy to verify that it actually came from the PUF.
  - leereeves 11y ago
    Do you have a source? I don't see that detail in the Wikipedia article and didn't find confirmation in a few Google searches.
    - vinceguidry 11y ago
      It's right there in the first sentence. > a physical unclonable function (PUF, sometimes also called physically unclonable function) is a physical entity that is embodied in a physical structure and is easy to evaluate but hard to predict.
      - leereeves 11y ago
        I'm not sure "evaluate" means "verify that it actually came from the PUF", though it is one possible interpretation.
        vinceguidry 11y ago
        Think of it like this. Forget that the PUF is a physical device and just consider the "function" part. A function is a piece of math that maps input to output. For example, f(x) = 2x. This function is easy to compute and easy to predict. A hash function is easy to compute but hard to predict. A function doesn't have to rely on any kind of arithmetic, you can have a random function that simply maps all inputs to random outputs, or something silly like a function that hands its input to a two-year old, who then points out a star in the sky, then an astronomer takes a picture and gives that as a return to the function. A Physically Unclonable Function is a function baked into hardware in a specific way that, like hash functions, allows computation but resists prediction. The article describes in a general sense how this is accomplished, by making the output of the function rely on impossible-to-replicate physical features of the circuit. Even though the actual output is unpredictable, you can still tell it's from the PUF due to purposefully-added design constraints.
        leereeves 11y ago
        I understand the idea, I'm just looking for confirmation - more than one vague, uncited sentence on Wikipedia whose meaning is unclear. Have you worked with these?
        vinceguidry 11y ago
        There's plenty of references at the bottom, why don't you dive into these yourself instead of asking me to do it for you? I found the article perfectly clear.
        leereeves 11y ago
        I ask because you seem to be acting like an expert. Have you based everything you said here solely on your interpretation of the Wiki article?

You would need to clone the device, as the possible challenges are infinite as they are mathematically-generated. The scheme would just be a glorified one time pad otherwise.

leereeves 11y ago

But what can be done with the challenges that uses the "infinite" set of possible challenges instead of a finite subset that has been stored on another device? In other words, if a fake responds with anything it wants for challenges that aren't stored on the other device (the challenger), how would the challenger know the response didn't match what the real PUF would send?

vinceguidry 11y ago
The responses are verified mathematically in a manner akin to a hash function. It's hard to know what the PUF will send, but easy to verify that it actually came from the PUF.
- leereeves 11y ago
  Do you have a source? I don't see that detail in the Wikipedia article and didn't find confirmation in a few Google searches.
  - vinceguidry 11y ago
    It's right there in the first sentence. > a physical unclonable function (PUF, sometimes also called physically unclonable function) is a physical entity that is embodied in a physical structure and is easy to evaluate but hard to predict.
    - leereeves 11y ago
      I'm not sure "evaluate" means "verify that it actually came from the PUF", though it is one possible interpretation.
      - vinceguidry 11y ago
        Think of it like this. Forget that the PUF is a physical device and just consider the "function" part. A function is a piece of math that maps input to output. For example, f(x) = 2x. This function is easy to compute and easy to predict. A hash function is easy to compute but hard to predict. A function doesn't have to rely on any kind of arithmetic, you can have a random function that simply maps all inputs to random outputs, or something silly like a function that hands its input to a two-year old, who then points out a star in the sky, then an astronomer takes a picture and gives that as a return to the function. A Physically Unclonable Function is a function baked into hardware in a specific way that, like hash functions, allows computation but resists prediction. The article describes in a general sense how this is accomplished, by making the output of the function rely on impossible-to-replicate physical features of the circuit. Even though the actual output is unpredictable, you can still tell it's from the PUF due to purposefully-added design constraints.
        leereeves 11y ago
        I understand the idea, I'm just looking for confirmation - more than one vague, uncited sentence on Wikipedia whose meaning is unclear. Have you worked with these?
        vinceguidry 11y ago
        There's plenty of references at the bottom, why don't you dive into these yourself instead of asking me to do it for you? I found the article perfectly clear.
        leereeves 11y ago
        I ask because you seem to be acting like an expert. Have you based everything you said here solely on your interpretation of the Wiki article?