RE: I-D ACTION:draft-laganier-ipv6-khi-00.txt

["Christian Huitema" <huitema at windows.microsoft.com>]

> We would appreciate very much feedback from members of the IPv6 WG on
> this internet draft.

I am supportive of the genral idea of reserving a prefix for
"statistically unique identifiers" that are derived from some kind of
cryptographic ID. However, I have a problem with the specified syntax:

   Input      :=  any bitstring
   Hash Input :=  Context ID | Input
   Hash       :=  SHA1( Expand( Hash Input ) )
   KHI        :=  Prefix | Encode_n( Hash )

This syntax includes a static reference to the SHA1 hash function and to
the "encode_n" extraction function. As a general rule, hard coding a
specific cryptographic algorithm in a standard is a very bad idea. In
fact, SHA1 is already suspect. The syntax should allow for an
identification of the algorithm as part of the "hash input".

I would much prefer seeing the syntax modified to explicitly allow for
an arbitrary hashing function, maybe something like:

   Input      :=  any bitstring
   Hash Input :=  Algorithms ID | Context ID | Input
   Hash       :=  Hash( Expand( Hash Input ) )
   KHI        :=  Prefix | Encode_n( Hash )

In the proposed syntax, "algorithms ID" identifies the hash function,
the expand function, and the encode_n function. It may also identify a
particular syntax for the Input data, e.g. whether some type of
certificate is expected. 

-- Christian Huitema

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