Re: [Trans] Verifying inclusion proof

IETF standards need to be unambiguous. Code is very helpful, but it is 
not a substitute
for a rigorous description of how to resolve the issue that Onderj raised.

Steve
>
> On Fri, Jun 26, 2015 at 3:29 PM, Ondrej Mikle <ondrej.mikle@nic.cz 
> <mailto:ondrej.mikle@nic.cz>> wrote:
>
>     Pardon me if I am asking something obvious, but I'm missing one
>     piece of
>     information for inclusion proof verification - the "placement" of each
>     node returned from "get-proof-by-hash" method in audit_path list
>     (whether it's left subtree or right subtree).
>
>     Since the hashing of concatenation of strings is not commutative, the
>     auditor needs to put the two partial tree hashes in correct order
>     to get
>     to the correct root hash.
>
>
> Yes, you're quite right.
>
>
>     I'd guess the placement of the missing nodes from audit_path could be
>     derived from leaf_index and tree_size, but can't see a straightforward
>     way to do it. The reference client does not implement this
>     verification
>     either.
>
> There are a couple of implementations of this in the o/s code base:
> C++ is in cpp/merkletree/merkle_verifier.cc 
> <https://github.com/google/certificate-transparency/blob/master/cpp/merkletree/merkle_verifier.cc> (see 
> VerifyPath())
> Python is in python/ct/crypto/merkle.py 
> <https://github.com/google/certificate-transparency/blob/master/python/ct/crypto/merkle.py> (see 
> verify_leaf_inclusion())
>
> HTH.
>
> Cheers,
> Al.
>
>     Ondrej
>
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