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Please Consider: English is my second language.


Background

I have been looking at different CP/CPS on the web. They all seem to roughly follow the same practices. However, two different policies differed: the first makes sense to me; the second… well, not so much.

Although I can have a vague idea on the rationale behind the second policy, I would like to really understand the different implications of each in order to make an informed decision as to how I would implement this.

Contrast

The first policy (the one that makes sense to me) is from Cisco. On page 22, section 6.2.9 Method of Destroying Private Key:

Upon expiration or revocation of a certificate, or other termination of use of a private key for creating signatures, all copies of the private key shall be securely destroyed.

The second policy, requires the private key not to be destroyed, but archived. It is from StartCom Ltd, on page 34’s second paragraph:

[…] CA private keys shall be archived after expiration of the public key according to the same procedure as the CA root key.

Question

My question is then: what would be rationale behind each, and what would be the possible implications of choosing one over the other?

1 Answer 1

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My gut feeling on this would be whether or not there should be recoverable access to archived, encrypted traffic or not.

Policy #1 (Destroying all copies of the private key) from Cisco is attempting to:

  • Prevent the old certificate / private key being stolen and used for some kind of spoofing / nefarious activity (even after expiration some things can be done)
  • Prevent an attacker from being able to gather a large amount of encrypted traffic over a period of time, then steal the archived private key at some point and decrypt old traffic

I'm not sure what benefit policy #2 would give besides allowing you to recover raw encrypted traffic at some later point if you needed to, after you've rotated the certs out.

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  • But Diffie-Hellman key exchange provides perfect forward secrecy so that even if a TLS certificate private key is stolen in the future, it cannot be used to decrypt saved encrypted traffic. Commented May 2, 2020 at 15:48

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