5 ms·

this is the standard "remote wipe" technique and a standard cryptographic application

gouggoug 8y ago
I know nothing about the "standard remote wipe technique", but neophyte me believes that wiping security keys isn't exactly protecting you against your data being eventually retrieved and decrypted.
- kerng 8y ago
  Agreed. In security, time works against mitigations. If you want data to be gone, just deleting keys is a bit short sighted.
  - varenc 8y ago
    This wouldn’t really improve security. Only the secure hardware is secure from physical attack. The user data is encrypted and put on memory that isn’t physically secure. If you have a way to decrypt that data, you can just physically remove that memory, copy that data, and break the encryption on it. If people could break encryption, they wouldn’t go about updating the firmware and triggering a potential data wipe in the first place. In short, if you don’t trust encryption you’ve already lost.
    - kerng 8y ago
      The thing I wanted to highlight is that time works against encryption. What is encrypted with today's most powerful and thorough understanding of crypto, will possibly be easily decrypted a few years or a decade down the road. So in addition to deleting the keys, I would always wipe the data itself also.
      - varenc 8y ago
        I agree that time works against crypto, but one point I wanted to make is that the attacker can easily prevent the data wipe from happening. Just physically copy the encrypted user data, or discount that memory from the device. It’s hard for me to an imagine a state funded attacker that wouldn’t just prevent the data wipe if they cared. I agree at least there’s an extreme edge case where this would protect you from a simultaneously very advanced but also negligent attacker, but that seems so rare that it’s unconcerning to me. Feels a bit like adding an extra luggage lock to a bank vault since its still better to have more security afterall...
- mcpherrinm 8y ago
  The data could be stored on an SD card, or emmc flash, or the cloud. Erasing is not reliable there. The more data you have to protect with secure hardware, the easier a time the attacker has. Destroying encryption keys stored in a small, secure processor is the most reliable and secure method. The encrypted data can and should be wiped too, but it's a lot more reliable to have your security model not rely on that. We have no reason to believe AES-256 will ever be broken within the lifetime of the universe. Maybe in 100 years I will be proven wrong, but I am willing to bet the security of my phone on it. I suspect we will have human beings living in another solar system before AES-128 is broken.
  - gouggoug 8y ago
    My point is about doing both, if possible, instead of just getting rid of the keys.
    - ethbro 8y ago
      Because, as parent noted, making it possible makes your secure enclave more complex (which is the same as less secure). Furthermore, as parent also noted, if your encryption is solid, wiping the keys is identical to wiping the data.
      - gouggoug 8y ago
        Indeed, my bad, I totally read his answer too fast and missed "The encrypted data can and should be wiped too, but it's a lot more reliable to have your security model not rely on that."

I know nothing about the "standard remote wipe technique", but neophyte me believes that wiping security keys isn't exactly protecting you against your data being eventually retrieved and decrypted.

kerng 8y ago
Agreed. In security, time works against mitigations. If you want data to be gone, just deleting keys is a bit short sighted.
- varenc 8y ago
  This wouldn’t really improve security. Only the secure hardware is secure from physical attack. The user data is encrypted and put on memory that isn’t physically secure. If you have a way to decrypt that data, you can just physically remove that memory, copy that data, and break the encryption on it. If people could break encryption, they wouldn’t go about updating the firmware and triggering a potential data wipe in the first place. In short, if you don’t trust encryption you’ve already lost.
  - kerng 8y ago
    The thing I wanted to highlight is that time works against encryption. What is encrypted with today's most powerful and thorough understanding of crypto, will possibly be easily decrypted a few years or a decade down the road. So in addition to deleting the keys, I would always wipe the data itself also.
    - varenc 8y ago
      I agree that time works against crypto, but one point I wanted to make is that the attacker can easily prevent the data wipe from happening. Just physically copy the encrypted user data, or discount that memory from the device. It’s hard for me to an imagine a state funded attacker that wouldn’t just prevent the data wipe if they cared. I agree at least there’s an extreme edge case where this would protect you from a simultaneously very advanced but also negligent attacker, but that seems so rare that it’s unconcerning to me. Feels a bit like adding an extra luggage lock to a bank vault since its still better to have more security afterall...
mcpherrinm 8y ago
The data could be stored on an SD card, or emmc flash, or the cloud. Erasing is not reliable there. The more data you have to protect with secure hardware, the easier a time the attacker has. Destroying encryption keys stored in a small, secure processor is the most reliable and secure method. The encrypted data can and should be wiped too, but it's a lot more reliable to have your security model not rely on that. We have no reason to believe AES-256 will ever be broken within the lifetime of the universe. Maybe in 100 years I will be proven wrong, but I am willing to bet the security of my phone on it. I suspect we will have human beings living in another solar system before AES-128 is broken.
- gouggoug 8y ago
  My point is about doing both, if possible, instead of just getting rid of the keys.
  - ethbro 8y ago
    Because, as parent noted, making it possible makes your secure enclave more complex (which is the same as less secure). Furthermore, as parent also noted, if your encryption is solid, wiping the keys is identical to wiping the data.
    - gouggoug 8y ago
      Indeed, my bad, I totally read his answer too fast and missed "The encrypted data can and should be wiped too, but it's a lot more reliable to have your security model not rely on that."