[aerogear-dev] iOS Crypto findings

[Christos Vasilakis]

Hi team,

I am digging on the CommonCrypto API and I found some issues. Specifically:

a)  GCM mode for AES symmetric encryption is part of a private API. See [1] the public interface of the current definitions of supported modes of operation. 'kCCModeGCM' is missing _although_ digging on the source code of the apple's web site it is defined in [2]  'private' (The file is included from a private interface here [3]).  Also here is the implementation of the GCM mode in [4] and test cases that exercise it [5]. Not sure why Apple left it out in public. On my search, one area in which they use this mode is on the KeyChain from iOS 5 onwards, see 'KeyChain' section here [6]

b) Generation of asymmetric  ECC keys and encryption is supported by CommonCrypto but _again_ under a private interface, see [7] and [8].  ECC is used in the protection class 'NSFileProtectionCompleteUnlessOpen' according to the iOS Security doc here [9]. In the meeting there was a plan B for it, RSA with Diffie Hellman. I am looking at it, but to my current knowledge is supported if you trust the apple docs here [10] 

My worry is how can we proceed with the first issue.

As a side note, during my search I discovered Crypto++ [11] , which seems to offer many of the features we are trying to support. Con is a C++ interface although an iOS distribution of it exists (see [12]), and there is an iOS wiki page in the library home page [13].  Needs more research.

Thanks,
Christos


[1] https://gist.github.com/cvasilak/b967893655a04cbe5b7b#file-gistfile1-txt-L667
[2] https://github.com/Apple-FOSS-Mirror/CommonCrypto/blob/master/Source/CommonCryptoSPI/CommonCryptorSPI.h#L70
[3] https://github.com/Apple-FOSS-Mirror/CommonCrypto/blob/master/Source/CommonCryptoSPI/CommonCryptoPriv.h
[4] https://github.com/Apple-FOSS-Mirror/CommonCrypto/blob/master/Source/API/CommonGCMCryptor.c
[5] https://github.com/Apple-FOSS-Mirror/CommonCrypto/blob/master/CCRegression/CommonCrypto/CommonCryptoSymGCM.c
[6] http://esec-lab.sogeti.com/post/iOS-5-data-protection-updates
[7] https://github.com/Apple-FOSS-Mirror/CommonCrypto/blob/master/Source/CommonCryptoSPI/CommonECCryptor.h
[8] https://github.com/Apple-FOSS-Mirror/CommonCrypto/blob/master/Source/API/CommonECCryptor.c
[9] http://www.apple.com/ipad/business/docs/iOS_Security_Oct12.pdf
[10]https://developer.apple.com/library/ios/documentation/security/conceptual/cryptoservices/CryptographyConcepts/CryptographyConcepts.html#//apple_ref/doc/uid/TP40011172-CH8-CHDCCDIA
[11] http://www.cryptopp.com
[12] https://github.com/noloader/cryptopp-5.6.2-ios
[13] http://www.cryptopp.com/wiki/IOS_(Xcode)
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