Bitcoin developer Gregory Maxwell writes the next on Reddit:
There’s a design flaw within the Bitcoin protocol the place its potential for a 3rd social gathering to take a legitimate transaction of yours and mutate it in a means which leaves it legitimate and functionally equivalent however with a unique transaction ID. This significantly complicates writing appropriate pockets software program, and it may be used abusively to invalidate lengthy chains of unconfirmed transactions that depend upon the non-mutant transaction (since transactions refer to one another by txid).
This challenge arises from a number of sources, one in all them being OpenSSL’s willingness to just accept and make sense of signatures with invalid encodings. A traditional ECDSA signature encodes two giant integers, the encoding isn’t fixed size— if there are main zeros you’re purported to drop them.
It’s simple to put in writing software program that assumes the signature will likely be a relentless size after which depart additional main zeros in them.
This can be a very attention-grabbing cautionary story, and is especially necessary as a result of conditions like these are a part of the explanation why we have now made sure design selections in our growth philosophy. Particularly, the difficulty is that this: many individuals proceed to convey up the purpose that we’re in lots of locations unnecessarily reinventing the wheel, creating our personal serialization format, RLP, as a substitute of utilizing the prevailing protobuf and we’re constructing an application-specific scripting language as a substitute of “simply utilizing Lua”. This can be a very legitimate concern; not-invented-here syndrome is a commonly-used pejorative, so doing such in-house growth does require justification.
And the cautionary story I quoted above supplies exactly the proper instance of the justification that I’ll present. Exterior applied sciences, whether or not protobuf, Lua or OpenSSL, are excellent, and have years of growth behind them, however in lots of circumstances they have been by no means designed with the proper consensus, determinism and cryptographic integrity in thoughts that cryptocurrencies require. The OpenSSL scenario above is the proper instance; except for cryptocurrencies, there actually is not any different conditions the place the truth that you may take a legitimate signature and switch it into one other legitimate signature with a unique hash is a major downside, and but right here it’s deadly. Considered one of our core ideas in Ethereum is simplicity; the protocol needs to be so simple as potential, and the protocol shouldn’t include any black packing containers. Each single function of each single sub-protocol needs to be exactly 100% documented on the whitepaper or wiki, and carried out utilizing that as a specification (ie. test-driven growth). Doing this for an present software program package deal is arguably virtually as onerous as constructing a wholly new package deal from scratch; in reality, it might even be more durable, since present software program packages typically have extra complexity than they should with the intention to be feature-complete, whereas our alternate options don’t – learn the protobuf spec and evaluate it to the RLP spec to know what I imply.
Be aware that the above precept has its limits. For instance, we’re definitely not silly sufficient to start out inventing our personal hash algorithms, as a substitute utilizing the universally acclaimed and well-vetted SHA3, and for signatures we’re utilizing the identical previous secp256k1 as Bitcoin, though we’re utilizing RLP to retailer the v,r,s triple (the v is an additional two bits for public key restoration functions) as a substitute of the OpenSSL buffer protocol. These sorts of conditions are those the place “simply utilizing X” is exactly the best factor to do, as a result of X has a clear and well-understood interface and there are not any refined variations between completely different implementations. The SHA3 of the empty string is c5d2460186…a470 in C++, in Python, and in Javascript; there’s no debate about it. In between these two extremes, it’s principally a matter of discovering the best steadiness.
