* [bitcoin-dev] Reinterpretations of contracts in different pay-to-contract schemes
@ 2018-09-03 9:26 ZmnSCPxj
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From: ZmnSCPxj @ 2018-09-03 9:26 UTC (permalink / raw)
To: bitcoin-dev
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Good morning all,
I am wondering if there is the possibility of an issue arising when different pay-to-contract schemes are used on Bitcoin.
Specifically, I wonder, if it may be possible to reinterpret the byte serialization of a contract under one scheme as the byte serialization of a different contract under another scheme. The user may expect to have committed to a contract under the first scheme, but is rudely made aware that she has also committed to a different contract under a scheme she is unaware of.
For instance, if some independent protocol uses pay-to-contract, it may be possible for the contract to be reinterpreted as a Bitcoin SCRIPT under Taproot, leading to a contract that can be reinterpreted as a Bitcoin SCRIPT and allowing a Bitcoin-level UTXO to be stolen without knowledge of the private key.
I thought of this a little while ago and mentioned it here:https://github.com/rgb-org/spec/issues/61
Now, it may be possible to use the hash of the contract, but if Taproot uses a hash of the script also and the same hash function is used, then the bytes of the contract could be reinterpreted as a Bitcoin SCRIPT program, possibly leading to a trivial-to-solve SCRIPT with enough hacking.
If this is indeed a concern, then I propose, that pay-to-contract schemes should pay to the below tweak:
Q = P + SHA256d(P || Scheme || C) * G
Where `Scheme` is 256 bits (32 bytes) scheme identifier. For Taproot, it could be the genesis block ID. Then other pay-to-contract schemes must ensure that they use a `Scheme` ID that is different with high probability from other `Scheme` IDs, in order to ensure that reinterpretation of contracts is impossible.
Regards,
ZmnSCPxj
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