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 occasion to take a legitimate transaction of yours and mutate it in a means which leaves it legitimate and functionally similar however with a distinct transaction ID. This significantly complicates writing right pockets software program, and it may be used abusively to invalidate lengthy chains of unconfirmed transactions that rely on the non-mutant transaction (since transactions refer to one another by txid).
This difficulty arises from a number of sources, certainly one of them being OpenSSL’s willingness to simply accept and make sense of signatures with invalid encodings. A traditional ECDSA signature encodes two massive integers, the encoding isn’t fixed size— if there are main zeros you might be presupposed to drop them.
It’s straightforward to put in writing software program that assumes the signature shall be a continuing size after which depart further main zeros in them.
It is a very attention-grabbing cautionary story, and is especially essential as a result of conditions like these are a part of the rationale why we’ve got made sure design selections in our growth philosophy. Particularly, the difficulty is that this: many individuals proceed to carry 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”. It is 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 right instance of the justification that I’ll present. Exterior applied sciences, whether or not protobuf, Lua or OpenSSL, are superb, and have years of growth behind them, however in lots of instances they had been by no means designed with the right consensus, determinism and cryptographic integrity in thoughts that cryptocurrencies require. The OpenSSL scenario above is the right instance; other than cryptocurrencies, there actually isn’t any different conditions the place the truth that you possibly can take a legitimate signature and switch it into one other legitimate signature with a distinct hash is a big drawback, and but right here it’s deadly. Certainly one of our core rules in Ethereum is simplicity; the protocol needs to be so simple as potential, and the protocol shouldn’t comprise any black containers. Each single characteristic 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 exhausting as constructing a completely new package deal from scratch; in truth, it could even be tougher, since present software program packages usually have extra complexity than they should in an effort to be feature-complete, whereas our alternate options don’t – learn the protobuf spec and examine 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 begin 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 fitting factor to do, as a result of X has a clear and well-understood interface and there are not any refined variations between totally 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 fitting steadiness.
