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I've been tasked with defining a list of cipher suites to use.

The requirements for the cipher suites are the following:

  • Symmetric Algorithm: AES-256
  • Key Exchange: ECDH P-384, DH 3072-bit, RSA 3072-bit
  • Key Authentication: ECDSA P-384, RSA 3072-bit
  • Hash Algorithm: SHA-384

Here is the list I've come up with (in prioritized order):

  1. TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 (0x00C02C)
  2. TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 (0x00C024)
  3. TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (0x00C030)
  4. TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 (0x00C028)
  5. TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x00009F)
  6. TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384 (0x00C02E)
  7. TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA384 (0x00C026)
  8. TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384 (0x00C032)
  9. TLS_ECDH_RSA_WITH_AES_256_CBC_SHA384 (0x00C02A)
  10. TLS_RSA_WITH_AES_256_GCM_SHA384 (0x00009D)
  11. TLS_DH_RSA_WITH_AES_256_GCM_SHA384 (0x0000A1)

Would you say I've made the correct prioritization of the cipher suites? Are any of these ciphers considered weak?

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    $\begingroup$ Uhm, why do you prioritize CBC over GCM? $\endgroup$ – SEJPM Mar 15 '17 at 16:41
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    $\begingroup$ I'd say [1] prefer GCM over CBC, [2] prefer ECDHE over ECDH over DH [3] prefer ECDSA over RSA. $\endgroup$ – puzzlepalace Mar 15 '17 at 17:41
  • $\begingroup$ @SEJPM, looks like a typo. 0x00C02C uses GCM. 4ndr345 , could you clarify? $\endgroup$ – otus Mar 15 '17 at 18:27
  • $\begingroup$ @otus A typo indeed. Edited the question to correct the mistake. $\endgroup$ – 4ndr345 Mar 15 '17 at 18:38
  • $\begingroup$ @puzzlepalace In regards to Key exchange, would you prefer DHE over ECDH or the other way around? And where would you rate RSA in there? $\endgroup$ – 4ndr345 Mar 15 '17 at 18:46
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These are all fine and the order seems reasonable as well. It is a judgement call which part you think is most likely to fail. I would use your order of preference for the elliptic curve algorithms. GCM vs. CBC is a case of which you find more likely to be badly implemented.

If the requirements are not enforced upon you, I would consider adding in P-256. It should be as strong as 3072-bit RSA, and it at least used to be slightly more widely supported than P-384 – I have not seen recent numbers though.

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  • $\begingroup$ Thanks for the response. I've decided to scrap most of the non-ephemeral ciphers as all services I have tested against that support these options also supports the ephemeral variants. I've also removed DHE as the services that will implement this list does not support DHE > 1024/2048 (my requirement is 3072). Here's my final list (in prioritized order): TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 TLS_RSA_WITH_AES_256_GCM_SHA384 $\endgroup$ – 4ndr345 Mar 17 '17 at 17:03

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