Re: [Linphone-developers] bzrtp support for AES with 256-bit keys

[Ben Sartor]

Hi Johan,

thanks for reviewing.

> Hi Ben,
> and thanks for the patch.
> 
> I had a quick look at it, very nice rework on the tests cases!
> 
> Few remarks:
> - I think we should stick to AES128 being the default (switch in
> bzrtpCrypto_getAvailableCryptoTypes). The user will set it to AES256 if
> needed.

Agreed, especially as it is possible to update bzrtp without updating 
mediastream2 this way.  Updated patches are attached.

 By the way, this is about bzrtp and (lib)linphone may still choose AES256 as 
default in the future.

> - You may want to export also the algorithm defines and not only the
> types in bzrtp.h (commit 4) otherwise the user won't be able to safely
> use the get/set functions.

Done.

> - We shall ensure that mandatory algorithms are always present in the
> context supported list, by either checking their presence in the input
> supportedTypes of bzrtp_setSupportedCryptoTypes and queing them at the
> end if they are missing or tweaking the selectCommonAlgo to add them if
> they are missing.(first one seems cleaner)
> 
> - Same kind of problem (which was already there before your patches)
> with the incoming HelloPacket parsing: we shall ensure that if the
> packet doesn't contain a mandatory algo, it is added at the end of the
> list as specified in the RFC section 5.2:
> "If a mandatory algorithm is not included in the list, it
>     is implicitly added to the end of the list for preference."
> Which means the in function bzrtp_packetParser, all the tests on
> messageData->xx == 0 to set the mandatory algo shall be replaced by
> something checking the presence of the mandatory algo in the
> messageData->xx field after parsing it from the packet.

Patches implementing this are attached.

Cheers,
 Ben

> - min function seems fine to me as it is.
> 
> I'll have to rework the mediastream patch as I've done some
> modifications in zrtp.c, they're in branch dev_dtls for now but will be
> merge to master soon.
> 
> regards,
> 
> johan
> 
> On 23/01/15 03:58, Ben Sartor wrote:
> > Hi Johan,
> > 
> > thanks for you answer. I have tried to implement things like you
> > suggested.
> > 
> > Patches 0001 and 0002 are unchanged.
> > 
> > Patches 0003 to 0005 add the the getter and setter you suggested.
> > 
> > Patches 0006 to 0009 implement the tests. I completely refactored the
> > function "test_algoAgreement". Is it ok for you to write tests this way?
> > 
> > Patches 0010 to 0012 are some code cleanup suggestions and were not
> > discussed before. Let me know what you think.
> > Is there a better place for the min-function? Maybe even a macro like
> > discussed here [1]? Is "__typeof__" ok?
> > 
> > [1] http://stackoverflow.com/questions/3437404/min-and-max-in-c
> > 
> > The mediastreamer2 patch of my initial post still applies and may be used
> > for testing.
> > 
> > Kind Regards,
> > 
> >   Ben
> >> 
> >> Hi Ben,
> >> 
> >>> Yes. Just to be sure, did you mean implementing functions like this:
> >>> 
> >>> void bzrtp_setSupportedCipherTypes(bzrtpContext_t *zrtpContext, uint8_t
> >>> availableTypes[7], const uint8_t availableTypesCount);
> >>> 
> >>> uint8_t bzrtp_getSupportedCipherTypes(bzrtpContext_t *zrtpContext,
> >>> uint8_t
> >>> availableTypes[7]);
> >> 
> >> Yes but you want to add an uint8_t algoType argument(just like
> >> bzrtpCrypto_getAvailableCryptoTypes function) to both of them in order
> >> to use the same function to get/set the available algos for block
> >> cipher/key exchange/SAS rendering/Hash.
> >> 
> >>>> This means we also must add a way to store the user configuration in
> >>>> linphone. I was thinking the easiest way would be to store it in the
> >>>> config file and access it only manually for now. I can implement this
> >>>> if
> >>>> you're lost on the way linphone manage the config file.
> >>> 
> >>> I haven't had a look to  linphone config file management, yet. Let's see
> >>> how far I get or if you find time first.
> >> 
> >> It's quite simple, but if you struggle tell me and I'll have a look at
> >> it when you're done with bzrtp. We can use an already existing config
> >> setting used to select SRTP protection profile(see misc.c const
> >> MSCryptoSuite * linphone_core_get_srtp_crypto_suites(LinphoneCore *lc);)
> >> for the block cipher algo selection and do something for the other algo
> >> types when needed.
> >> 
> >>>> Last, this must be covered by automatic tests.(Key exchange between two
> >>>> users using different set of cipher block algo)
> >>> 
> >>> I'm not sure what you mean: Would you prefer a test similar to the
> >>> existing
> >>> "test_algoAgreement" or would it be better to write a test for the
> >>> function
> >>> "selectCommonAlgo" directly?
> >> 
> >> I was thinking of extending the test_algoAgreement to include block
> >> cipher selection and some test on linphone call to check correct reading
> >> of the configuration from file, but it can't harm to have a test for the
> >> selectCommonAlgo too.
> >> 
> >> Thanks for your contribution.
> >> 
> >> Have a good day
> >> 
> >> johan
> >> 
> >> _______________________________________________
> >> Linphone-developers mailing list
> >> address@hidden
> >> https://lists.nongnu.org/mailman/listinfo/linphone-developers
> > 
> > _______________________________________________
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> > address@hidden
> > https://lists.nongnu.org/mailman/listinfo/linphone-developers
> 
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0001-fixed-cipher-algorothm-type-parsing-of-AES3.patch
Description: Text Data

0002-added-cipher-algorithm-AES-with-256-bit-keys-AES3.patch
Description: Text Data

0003-selectCommonAlgo-now-is-a-global-function.patch
Description: Text Data

0004-zrtp-crypto-types-are-public-now.patch
Description: Text Data

0006-reactivated-tests-suites-of-Crypto-Wrappers-and-Cryp.patch
Description: Text Data

0005-added-getter-and-setter-for-supported-crypto-types.patch
Description: Text Data

0007-test-algoAgreement-now-checks-more-cases-for-key-agr.patch
Description: Text Data

0008-new-test-for-getter-setter-of-supported-crypto-types.patch
Description: Text Data

0009-packet-parser-now-checks-maxium-of-7-algorithm-types.patch
Description: Text Data

0010-selectCommonAlgo-now-makes-sure-to-not-return-an-arr.patch
Description: Text Data

0011-selectCommonAlgo-now-prevents-adding-the-same-elemen.patch
Description: Text Data

0012-updated-and-added-more-tests-for-mandatory-algo-type.patch
Description: Text Data

0013-make-sure-mandatory-algorithm-types-are-always-suppo.patch
Description: Text Data

0014-added-test-for-addMandatoryCryptoTypesIfNeeded.patch
Description: Text Data

0015-Code-Cleanup-fixed-typo-lenght-in-comments.patch
Description: Text Data