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I read another question about an embedded https daemon, which got me wondering:

How might one maintain secrecy about the private key within such an embedded system?

My logic is: If the device ships with the key inside it, and someone can obtain [a version of] the physical device, they can get the data out of it (including the RSA private key.) Right?

Once they have the private key:

  1. What stops them from sniffing your network traffic, and decrypting everything you send to the server?
  2. What stops them from pretending to be the device (MITM attack)?
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Yes, they can likely manage to extract your private key from the device. Even if you encrypt the key and don't keep the decryption key on the device (eg: you must enter a password to decrypt the key when you boot), there are techniques for extracting the key (eg: cold boot attacks). And, depending on the deployment scenario, you may not even be able to force a password to be entered on boot. In the end, there's no security without physical security.

In answer to your question:

What stops them from sniffing your network traffic, and decrypting everything you send to the server?

The ability to sniff TLS traffic in the face of a disclosed private key can be prevented by using TLS ciphers that support perfect forward secrecy. In these ciphers, the private key is only used for authentication and not encryption.

What stops them from pretending to be the device (MITM attack)?

Nothing (unless you have physical and virtual network infrastructure that ensures that an MiTM can't occur - this likely requires a secure network).

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