Richard,
You still need to address the case of using ECDH-ES plus a KDF to get the CEK directly. I.e. not using a KEK step. Jim From: Richard Barnes [mailto:[email protected]] Sent: Friday, July 19, 2013 10:26 AM To: John Bradley Cc: Jim Schaad; Mike Jones; [email protected] Subject: Re: [jose] 192 bit AES keys I wasn't saying that it should be a separate parameter. It's just not necessary in a lot of cases. If you have a 16-octet value in "encrypted_key", then you don't need to specify the key length; you could just say "AES-GCM", and the implementation would know it was AES-128-GCM based on the length of the key. Worse, as it is, there can be conflict. What should an implementation do with "enc":"A128GCM" with a 32-octet "encrypted_key"? Use the first 16 octets? The last? Reject? OTOH, for the cases where a KEK is derived, you do need to specify a key length for the KEK. So you could either do (1) "ECDH-ES+AES-KW" with a "dkLen" parameter (as in PKCS#5), or (2) "ECDH-ES+A128KW". If I were designing from clean slate, I would prefer #1, but I can live with #2. PROPOSAL: Remove key lengths in cases where it's not required ("A*GCM", "A*KW", "A*GCMKW"), since the length of the key will be clear from the "encrypted_key" value (or for "dir", from provisioning). Leave them in the "alg" values, since you need to specify key length there. PROS: -- Mitigate combinatorial explosion (don't need one identifier per key type) -- Avoid conflict issues -- Save 3 octets if you don't care about being pretty ("AGCM" instead of "A128GCM", though I would prefer "AES-GCM") -- Parallelism with the JWS algorithms (e.g., "HS256"), which don't specify key length CONS: -- Requires existing implementations to support additional algorithm identifiers (note: doesn't preclude supporting the old algorithm identifiers!) On Fri, Jul 19, 2013 at 1:13 PM, John Bradley <[email protected]> wrote: +1 I don't think taking the length out of the algorithm and making it a separate parameter is a good way to go. On 2013-07-19, at 1:11 PM, "Jim Schaad" <[email protected]> wrote: We need to keep key lengths in algorithm ids for the purpose of key derivation. Additionally there would need to be some way to signal the key length to the system when doing key generation i.e. you would need to change jose.SetCEKAlgorithm("AES128") to jose.SetCEKAlgoirthm("AES", 128) jim From: [email protected] [mailto:[email protected]] On Behalf Of Richard Barnes Sent: Friday, July 19, 2013 9:47 AM To: John Bradley Cc: Mike Jones; [email protected] Subject: Re: [jose] 192 bit AES keys Or we could just remove the key lengths from the algorithm IDs altogether ;) They really don't add any value. On Thu, Jul 18, 2013 at 6:17 PM, John Bradley < <mailto:[email protected]> [email protected]> wrote: I am OK with registering the 192 bit versions. Sent from my iPhone On Jul 18, 2013, at 5:17 PM, Mike Jones < <mailto:[email protected]> [email protected]> wrote: Richard had previously requested that we register algorithm identifiers for AES using 192 bit keys. As he previously pointed out, "It seems like if we're going to support AES, then we should support AES. Every AES library I know of supports all three key lengths, so it's not like there's extra cost besides the registry entry." (I'll note that we already have algorithm identifiers for the "mid-size" HMAC and signature functions "HS384", "RS384", and "ES384".) I heard no objections at the time. I'm therefore thinking that we should register algorithm identifiers for these key sizes as well. Specifically, we would add: "A192KW", "ECDH-ES+A192KW", "A192GCMKW", "PBES2-HS256+A192KW", "A192CBC-HS384", and "A192GCM". Support for these algorithms would be optional. What do people think? -- Mike _______________________________________________ jose mailing list <mailto:[email protected]> [email protected] <https://www.ietf.org/mailman/listinfo/jose> https://www.ietf.org/mailman/listinfo/jose _______________________________________________ jose mailing list <mailto:[email protected]> [email protected] <https://www.ietf.org/mailman/listinfo/jose> https://www.ietf.org/mailman/listinfo/jose
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