On Mon, May 22, 2017 at 10:41:40AM -0400, Ethan Heilman wrote: > >It'd help your case if you gave us some examples of such scripts being > used. > > I want OP_CAT so that I can securely and compactly verify many hashes and > hash preimages. This would shrink offchain Tumblebit transactions > significantly. > > For instance if I want a transaction TxA which checks that a transaction > TxB releases preimages x1,x2,...,x10 such that > y1=H(x1), y2=H(x2),...,y10=H(x10). Currently I just put y1,...y10 and check > that the preimahes hash correctly. With OP_CAT I would only have to store > one hash in TxA, yhash > > ytotal = H(OP_CAT(H(OP_CAT(y1, y2)),y3)...y10) > > TxA could then just hash all the preimages supplied by TxB and confirm they > hash to TxA. This would reduce the size of TxA from approx 10*32B to > 32+10*16B. I have a version which improves this further but it is more > complex. > > Most of the math OP codes aren't particularly helpful due to their 32bit > nature and their strange overflow behavior.
Great! That's exactly the type of justifying use-case we need for a BIP. An OP_CAT will have to have limits on maximum output size; how big an output does your application need? -- https://petertodd.org 'peter'[:-1]@petertodd.org
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