Bitcoin developer Gregory Maxwell writes the next on Reddit:
There’s a design flaw within the Bitcoin protocol the place its doable for a 3rd celebration to take a sound transaction of yours and mutate it in a means which leaves it legitimate and functionally an identical however with a distinct transaction ID. This drastically complicates writing appropriate 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 concern arises from a number of sources, one in every 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’re imagined to drop them.
It’s simple to jot down software program that assumes the signature will probably be a relentless size after which depart further main zeros in them.
This can be a very fascinating 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 choices in our growth philosophy. Particularly, the problem 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 present 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 gives 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 instances they had been by no means designed with the proper consensus, determinism and cryptographic integrity in thoughts that cryptocurrencies require. The OpenSSL state of affairs above is the proper instance; other than cryptocurrencies, there actually isn’t any different conditions the place the truth that you possibly can take a sound signature and switch it into one other legitimate signature with a distinct hash is a big downside, and but right here it’s deadly. Considered one of our core rules in Ethereum is simplicity; the protocol must be so simple as doable, and the protocol shouldn’t include any black bins. Each single characteristic of each single sub-protocol must be exactly 100% documented on the whitepaper or wiki, and applied utilizing that as a specification (ie. test-driven growth). Doing this for an present software program package deal is arguably nearly as arduous as constructing a completely new package deal from scratch; actually, it could even be tougher, since present software program packages typically have extra complexity than they should with a view to be feature-complete, whereas our options don’t – learn the protobuf spec and examine it to the RLP spec to grasp what I imply.
Notice that the above precept has its limits. For instance, we’re actually 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 suitable factor to do, as a result of X has a clear and well-understood interface and there are not any delicate 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 suitable steadiness.
