Subject: Re: [bitcoin-dev] Fast Merkle Trees

From: Mark Friedenbach <[email-masked]>
Date: Wed, 6 Sep 2017 19:20:06 -0700

This design purposefully does not distinguish leaf nodes from internal nodes. That way it chained invocations can be used to validate paths longer than 32 branches. Do you see a vulnerability due to this lack of distinction?

> On Sep 6, 2017, at 6:59 PM, Russell O'Connor <[email-masked]> wrote:
> 
> The fast hash for internal nodes needs to use an IV that is not the standard SHA-256 IV. Instead needs to use some other fixed value, which should itself be the SHA-256 hash of some fixed string (e.g. the string "BIP ???" or "Fash SHA-256").
> 
> As it stands, I believe someone can claim a leaf node as an internal node by creating a proof that provides a phony right-hand branch claiming to have hash 0x80000..0000100 (which is really the padding value for the second half of a double SHA-256 hash).
> 
> (I was schooled by Peter Todd by a similar issue in the past.)
> 
>> On Wed, Sep 6, 2017 at 8:38 PM, Mark Friedenbach via bitcoin-dev <[email-masked]> wrote:
>> Fast Merkle Trees
>> BIP: https://gist.github.com/maaku/41b0054de0731321d23e9da90ba4ee0a
>> Code: https://github.com/maaku/bitcoin/tree/fast-merkle-tree