Re: [secdir] SecDir review of draft-ietf-jose-cookbook-06
Yaron Sheffer <yaronf.ietf@gmail.com> Tue, 09 December 2014 20:40 UTC
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Date: Tue, 09 Dec 2014 22:40:03 +0200
From: Yaron Sheffer <yaronf.ietf@gmail.com>
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To: ⌘ Matt Miller <mamille2@cisco.com>, IETF Security Directorate <secdir@ietf.org>, The IESG <iesg@ietf.org>, draft-ietf-jose-cookbook.all@tools.ietf.org
References: <5470E68D.3040204@gmail.com> <547E36ED.1020205@cisco.com> <5480CD20.6080300@gmail.com> <548740F1.4010607@cisco.com>
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Subject: Re: [secdir] SecDir review of draft-ietf-jose-cookbook-06
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Hi Matt, Yes, I believe it does. I will respond to Jim's mail separately. Thanks, Yaron On 12/09/2014 08:35 PM, ⌘ Matt Miller wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA512 > > Hello Yaron, > > I believe < https://tools.ietf.org/html/draft-ietf-jose-cookbook-07 > > addresses most of your comments; the exceptions being those points > still under discussion (see Jim Schaad's latest reply). Please let me > know if I missed anything I thought I fixed. > > > Thank you, > > - -- > - - m&m > > Matt Miller < mamille2@cisco.com > > Cisco Systems, Inc. > > On 12/4/14, 2:07 PM, Yaron Sheffer wrote: >> Hi Matt, >> >> Please see my comments below. I have removed much of the original >> text, and only left points that need further discussion. >> >> Thanks, Yaron >> >> On 12/03/2014 12:02 AM, ⌘ Matt Miller wrote: [...] >>>> >>>> • Unless I missed it, the document does not mention a machine >>>> readable repository of these examples, which I am sure the >>>> author has created while writing the draft. Making such a >>>> repository publicly available would result in a much more >>>> useful resource than the current document, which essentially >>>> requires testers to scrape the document when creating their >>>> test cases. >>>> >>> >>> You did not miss it; I don't have a such a repository right now, >>> but I can put one together. Would something on github.com be >>> acceptable, or is there a better suggestion? >> >> GitHub would be a great place. >> >>> >>>> • (Not a comment to the current document:) I wonder why there >>>> is nothing explicit to distinguish a public key from a private >>>> key, and they are only distinguished by the presence or absence >>>> of several parameters, something that will not be natural to >>>> most developers. PEM is doing it very well: "-----BEGIN RSA >>>> PRIVATE KEY-----". >>>> >>>> • 3.4: the text is contradictory re: zero-padding of the value >>>> "d". Is it using the minimum number of octets, or exactly 256 >>>> octets (for a 2048-bit key)? >>>> >>> >>> The intent is that "d" is not zero-padded, and I overqualified in >>> my text. Would the following be acceptable? >>> >>> For a 2048-bit key, the field "n" is 256 octets in length when >>> decoded and the field "d" is not longer than 256 octets in length >>> when decoded. >>> >> >> Yes. >> >>> >> [snip] >>> >>>> • 5.1.1: since this is a "cookbook", we should be using the >>>> public key, not the private key. A private key would only be >>>> used in rare cases. Similarly 5.2.1. >>>> >>> >>> The private keys are included for both reproduction (which only >>> needs the public key) and verification (which necessitates the >>> private key). >>> >>> If I can put an online repository together, I can change the >>> examples to just include the public keys; otherwise would the >>> following in 5.1 (and 5.2) be sufficient? >>> >>> Note that only the RSA public key is necessary to perform the >>> encryption. However, the example includes the RSA private key >>> to allow readers to validate the example's output. >>> >> >> I'm fine with this new text. >> >>> >>>> • 5.3.1: the "plaintext content" is a list of keys, which is >>>> either confusing to the reader, or an actual error in the >>>> document. >>>> >>> >>> It is not in error. The most common usecase for password-based >>> encryption was the import and export of key sets, and the >>> Working Group desired a thorough example. >>> >>> Would it help if the following is added to 5.3? >>> >>> A common use of password-based encryption is the import/export >>> of keys. Therefore this example uses a JWK Set for the >>> plaintext content instead of the plaintext from figure 72. >>> >> >> Yes, this would help. >> >>> >>>> • 5.3.5: In the General Serialization version, I don't >>>> understand why only the encrypted key is per-recipient. I would >>>> expect the PBES2 parameters too (e.g., the salt) to be >>>> per-recipient. Presumably each of them is using a different >>>> password, and there's no reason to use a common salt. Similarly >>>> in 5.4.5. >>>> >>> >>> For compatibility across serializations (compact, general JSON, >>> flattened JSON), all of the parameters need to be in the JWE >>> Protected Header. In the general serialization, that means only >>> the "encrypted_key" field is present for the (presumably) sole >>> recipient. >>> >>> Would it be acceptable if the following were added to 5.3? >>> >>> Note that if password-based encryption is used for multiple >>> recipients, it is expected that each recipient use different >>> values for the PBES2 parameters "p2s" and "p2c". >>> >> >> So I still don't understand: don't we need an example that >> demonstrates how the JSON structure (or multiple structures) is >> generated so that "each recipient use(s) different values"? >> >> In general I don't understand this "compatibility" thing. >> Obviously there are some cases that cannot be expressed in all >> serialization types. Otherwise why would we need three of them? >> >>>> • 5.7: same as above, it makes sense for the per-recipient key >>>> to have an ID, rather than the content encryption key >>>> (typically an ephemeral key). And then that ID should be in the >>>> per-recipient data in 5.7.5. And similarly for 5.8. The later >>>> Sec. 5.13 shows a syntax for multiple recipients that's >>>> inconsistent with the single-recipient case, which would make >>>> sense if we got rid of the array. >>>> >>> >>> For compatibility across serializations (compact, general JSON, >>> flattened JSON), all of the parameters need to be in the JWE >>> Protected Header. Also, the mixing of "recipients" and >>> "encrypted_key"/"header" in the top-level object is not permitted >>> for the general serialization. >>> >> >> Still confused. Sorry. >> >>>> • 5.11: this example seems strange to me - why would anybody >>>> NOT want to integrity-protect the key ID and algorithm? I would >>>> prefer a more realistic example, or failing that, a >>>> recommendation to developers to avoid this practice. Similarly >>>> 5.12, which is an even worse idea. >>>> >>> >>> Integrity protection was thoroughly discussed in the JOSE WG. >>> While there are some limited attacks possible when some >>> parameters are unprotected, the WG felt there were enough use >>> cases where these attacks are mitigated through other means that >>> integrity protection of the part of all of the header is not >>> always required. >> >> So (personal opinion here) I think the WG took a security risk >> that should not have been taken in 2014, for a minor performance >> gain. We have seen too many protocols fail because of >> integrity-protection shortcuts. Who would have thought you need to >> integrity-protect the padding field! The fact that CMS took this >> route back in 1999 is sort of irrelevant, as we've all learned a >> lot since then. > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG/MacGPG2 v2.0.22 (Darwin) > Comment: GPGTools - https://gpgtools.org > > iQEcBAEBCgAGBQJUh0DxAAoJEDWi+S0W7cO1yn8H/3qu51pBi99f8FmuI/ZyW+9+ > LJfToPCcaTlSWqLR14mzApvm2VTgX60R89+ykQzVcvRIqZZvr4gqtJFnNtSUsGgs > PWEU837QEi0B/xfLADk6YF8om3B5XR6SX1xS4BSY4+oxh1XjIeRFoNqE2XLcFCd/ > P5NLs5NH3ZJS4khKFTgw7dzYBiSWUf+DEOZaPb8vcRVRUy7giJlKbax5u1jQgk9X > 1e7+W72rpjSVfd9+cP7Jme4Atz/K7MKawebz+6UsTVRH3dImwg4qy2IggMrGxrba > TZXdXE4wxVVlbc768cTjZJPtHwZ/HH/e/sgNrUK66WSrBveoBDf7v8NGu7+pS8w= > =3XEs > -----END PGP SIGNATURE----- >
- [secdir] SecDir review of draft-ietf-jose-cookboo… Yaron Sheffer
- Re: [secdir] SecDir review of draft-ietf-jose-coo… ⌘ Matt Miller
- Re: [secdir] SecDir review of draft-ietf-jose-coo… Richard Barnes
- Re: [secdir] SecDir review of draft-ietf-jose-coo… Jim Schaad
- Re: [secdir] SecDir review of draft-ietf-jose-coo… Yaron Sheffer
- Re: [secdir] SecDir review of draft-ietf-jose-coo… Jim Schaad
- Re: [secdir] SecDir review of draft-ietf-jose-coo… ⌘ Matt Miller
- Re: [secdir] SecDir review of draft-ietf-jose-coo… Yaron Sheffer