ISSUE-27: Specification of AES-CTR mode counter bits

aes ctr

Specification of AES-CTR mode counter bits

State:

CLOSED

Product:

crypto for Web Crypto API

Raised by:

Ryan Sleevi

Opened on:

2012-08-22

Description:

Under the AesCtrParams [1], callers can currently specify an initial value for the counter, as well as a length for how many bits are used for the block counter. Such a specification matches the PKCS#11 definition for AES-CTR, although other APIs such as CDSA, CryptoAPI, and CNG, do not support explicit counter mode, and instead only support ECB as a foundation for CTR.

However, by only specifying the length in bits of the counter, it presumes that the counter bits are either in the most-significant or least-significant bytes. Different systems using AES-CTR may place the block counter in different places - some using the MSB, others using the LSB. Thus, should the API specify an 'offset' as well that, when combined with length, gives a clear position of where the block counter is (internally managed by the API), and where the message counter/nonce are (externally managed by the caller)

[1] http://www.w3.org/2012/webcrypto/WebCryptoAPI/#dfn-AesCtrParams

Related Actions Items:

• ACTION-56 on Wan-Teh Chang to Write proposal for ISSUE-27 - due 2012-10-15, closed

Related emails:

1. Re: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from wtc@google.com on 2012-10-25)
2. W3C Web Crypto WG - agenda for 22nd of october call - today (from Virginie.GALINDO@gemalto.com on 2012-10-22)
3. [minutes] 15 October WebCrypto Call (from wseltzer@w3.org on 2012-10-17)
4. Re: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from wtc@google.com on 2012-10-16)
5. W3C Web Crypto WG - Take Away from 16th of Oct call (from Virginie.GALINDO@gemalto.com on 2012-10-16)
6. RE: W3C Web Crypto WG - agenda for 15th of october call - today (from Vijay.Bharadwaj@microsoft.com on 2012-10-15)
7. RE: W3C Web Crypto WG - agenda for 15th of october call - today (from Asad.Ali@gemalto.com on 2012-10-15)
8. Re: W3C Web Crypto WG - agenda for 15th of october call - today (from rbarnes@bbn.com on 2012-10-15)
9. Re: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from sleevi@google.com on 2012-10-15)
10. Re: W3C Web Crypto WG - agenda for 15th of october call - today (from S.Durbha@cablelabs.com on 2012-10-15)
11. Re: W3C Web Crypto WG - agenda for 15th of october call - today (from wtc@google.com on 2012-10-15)
12. Re: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from wtc@google.com on 2012-10-15)
13. Re: W3C Web Crypto WG - agenda for 15th of october call - today (from mountie.lee@mw2.or.kr on 2012-10-15)
14. W3C Web Crypto WG - agenda for 15th of october call - today (from Virginie.GALINDO@gemalto.com on 2012-10-15)
15. W3C Web Crypto - classifying issues - a new proposal (from Virginie.GALINDO@gemalto.com on 2012-09-22)
16. Re: W3C Web Crypto - classifying issues - a new proposal (from sleevi@google.com on 2012-09-21)
17. RE: W3C Web Crypto - classifying issues - a new proposal (from Virginie.GALINDO@gemalto.com on 2012-09-21)
18. W3C Web Crypto WG - Support for ECB (from Virginie.GALINDO@gemalto.com on 2012-09-10)
19. RE: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from Vijay.Bharadwaj@microsoft.com on 2012-09-04)
20. Re: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from wtc@google.com on 2012-08-31)
21. RE: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from Vijay.Bharadwaj@microsoft.com on 2012-08-28)
22. Re: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from wtc@google.com on 2012-08-27)
23. Re: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from sleevi@google.com on 2012-08-27)
24. RE: crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from Vijay.Bharadwaj@microsoft.com on 2012-08-27)
25. crypto-ISSUE-27 (aes ctr): Specification of AES-CTR mode counter bits [Web Cryptography API] (from sysbot+tracker@w3.org on 2012-08-22)

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