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So without giving too much away, the basics are that I have a board that needs an operating system, so I go to an IPL server to supply that operating system.

I have a verifier in the middle and my idea is to encrypt the download from the IPL and send it to the verifier, then the verifier encrypts it again with a different encryption method so that when it gets to the original board, the board decrypts it twice.

Short question is it possible to encrypt a download twice, once with two different encryption methods so that it would be even more difficult to break/easier to verify if there was tampering involved?

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    Encryption does not prevent tampering. To reliably detect tampering, you need a MAC.
    – Tom Leek
    Commented Jun 17, 2015 at 19:23
  • Do you control the IPL? How/when will you perform the first encryption? Have you considered digitally signing the file?
    – schroeder ♦
    Commented Jun 17, 2015 at 19:23
  • Yes I control all three systems, the board, the verifier, and the IPL, and yes sorry we are signing the file.
    – Puddinglord
    Commented Jun 17, 2015 at 20:17

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Yes, absolutely. You can re-encrypt an encrypted file however you'd like. For example, if you'd like to encrypt it once with asymmetric (public-key) encryption, and then again with symmetric (password), you'd need both a password and a private key to decrypt it. The same would be true if you encrypted it multiple times with symmetric encryption (multiple passwords, a new one each time a layer of the onion so to speak is peeled back), or keys (multiple public keys, again, onion-esque).

That said, I think any benefit to the multiple methods of encryption is only going to be marginally beneficial. A strong cryptosystem in the first place sounds like the best solution, e.g. 4096 bit rsa, or 256-bit elliptic curve. I'm not sure this approach solves your problem though.

Remember, each board needs to have a different key and you can't share the same private key or symmetric key with each piece of hardware without creating a huge security hole. In such a way, updates should be signed with a private key only you (the master code distributor) possess and the boards should validate the signature in traditional code-signing fashion.

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Yes 100%. You can do this with any encryption algorithm you'd like. My personal favorite is to PGP encrypt a file then on top of that encrypt it with 4096-bit RSA. Something to hide that it's PGP encrypted and also little extra security if my key get's into the wrong hands.

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