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I'm terminating SSL/TLS in my DMZ and I have to assume that machine will be hacked. At which point my certificates are compromised.

Previously I've used nCipher hardware keystore/accelerator to solve this issue. These cards won't reveal the private key even to root. The card performs the encryption and decryption onboard and is hardened against physical attack. The only way to get at the keys is by attaching a smart card reader to the card itself.

I'm having trouble finding information about something to recreate this approach. Is this the domain of specialist switches and firewalls these days?

This old page references some of the old hardware:

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It occurs to me that there may be a possibility to do this with virtual hardware, as I'm running on VMWare ESXi. However I kinda have to assume that will be hacked too. – byeo May 10 '12 at 16:21
"and I have to assume that machine will be hacked" +1 for looking that possibility in the eye! – rackandboneman May 10 '12 at 17:53

If you've chosen your SSL implementation, then it will constrain your choice of hardware. Favor hardware that has been supported long-term by the official release, as-is.

Before bothering with tamper-resistant hardware to protect your keys, it's worth considering some other issues:

A stolen certificate is only useful while DNS is also hijacked. (SSL uses Diffie-Hellman to prevent passive attacks, so the thief would need to be an active Man-in-the-Middle, impersonating you.)

SSL is only as secure as the weakest CA (Certificate Authority) that it trusts. Browsers had 2 major CAs (Comodo, DigiNotar) publically compromised in the past 2 years. If possible (not in web commerce, obviously), install your certificate without a CA.

Apply the shortest practical expiration time for your certificates.

Someone who breaks into your SSL terminator does not need your certificate to do major harm. He can hide there, funnel and filter traffic (e.g. taking credit card numbers), and use steganography to undetectably retrieve the result.

Commercial crypto hardware has a terrible security record. There have been timing attacks, fault injection (voltage, radiation) attacks, and traditional bugs. They are closed, for-profit products; they have strong motive to conceal flaws -- as revealed dramatically in the case of RSA SecureID.

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