CIP-???? | On-Chain Parameter Application

CIP-param-application/README.md

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+---
+CIP: ????
+Title: On-Chain Parameter Application
+Status: Proposed
+Category: Plutus
+Authors:
+    - Philip DiSarro <[email protected]>
+    - Keyan M. <[email protected]>
+    - Microproofs <[email protected]>
+Implementors: []
+Discussions: 
+    - https://github.com/cardano-foundation/CIPs/pull/934/
+Created: 2024-11-06
+License: CC-BY-4.0
+---
+
+## Abstract
+We propose a new Plutus builtin function `builtinApplyParams` with the
+signature `BuiltinByteString -> [BuiltinByteString] -> BuiltinByteString` in
+order to enable simple and low cost on-chain check for validating instances of
+unapplied scripts.
+
+## Motivation: why is this CIP necessary?
+Complex contracts tend to depend on multiple scripts, and in some cases,
+validation from scripts with some unknown parameters are required.
+
+As a simple example, assume a minting script which needs to validate that the
+destination of its token is a parameterized spending script that is uniquely
+instantiated for a user.
+
+The [current solution](#alternatives), is costly and relatively complex. With
+our proposed builtin function, the minting script of the example above can
+be provided with the unapplied script (either directly or indirectly), and have
+arbitrary values applied to it as parameters.
+
+## Specification
+
+### Function Definition
+
+We propose the Plutus builtin function `builtinApplyParams`, with the following
+type signature:
+```hs
+builtinApplyParams :: BuiltinByteString -> [BuiltinByteString] -> BuiltinByteString
+```
+
+Where the first argument is the unapplied script's CBOR, and
+the `BuiltinByteString` list is CBOR bytes of all the parameters that are to be
+applied in order. Finally, output will be the fully/partially applied script
+CBOR.
+
+
+### Cost Model
+
+TODO
+
+
+## Rationale: how does this CIP achieve its goals?
+
+Using the [provided example](#motivation-why-is-this-cip-necessary), the minting
+script can have access to the unapplied script:
+* Either by direct inclusion as a parameter (which can lead to a large script size)
+* Or providing a UTxO as a parameter that houses the unapplied script so that
+  the minting script can read it without becoming excessively large
+
+Furthermore, arbitrary parameters can be provided via the redeemer which can be
+used to generate an instance's script hash.
+
+In short, we'll get:
+* Easier and cheaper parameter verification on-chain
+* A more automation-friendly build for such architectures
+* Less error prone builds
+
+### Alternatives 
+
+Implementing such a validation on-chain would involve a few steps.
+
+First, the whole target contract has to be wrapped within an outer function
+which the parameters will be applied to. This leads to single occurances of
+the parameters throughout the script's CBOR.
+
+Secondly, each parameter will be required to have fixed lengths in order to
+allow validation of the bytes surrounding parameters. This can be achieved by
+assuming these parameters are all hashes, and that their corresponding values
+will be provided via the redeemer.
+
+Next, in order to validate a given script is an instance of a known script,
+first bytes of an instance must be provided (up until where the parameters are
+placed). With this "prefix" at hand, the instance's CBOR can be constructed
+on-chain as such:
+```hs
+let appliedCBOR =
+  prefix <> param0 <> paramHeader <> param1 <> paramHeader <> param2 <> postfix
+```
+
+Where `postfix` is similar to `prefix`, but for the rest of the script until its
+end. Note that `paramHeader` can be reused based on the presumption that all
+parameters are of equal lengths.
+
+Finally, this `appliedCBOR` can be hashed to attain its corresponding script
+credential.
+
+## Path to Active
+
+### Acceptance Criteria
+- [] Fully implemented in Cardano.
+
+### Implementation Plan
+- [] Passes all requirements of both Plutus and Ledger teams as agreed to improve Plutus script efficiency and usability.
+
+## Copyright
+This CIP is licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/legalcode).
+
+[CC-BY-4.0]: https://creativecommons.org/licenses/by/4.0/legalcode
+[Apache-2.0]: http://www.apache.org/licenses/LICENSE-2.0