cryptoscript

cryptoscript is a non-turing complete DSL used for policy-as-code. It will typically be embedded within an authorization capability as the primary caveat representing the predicate conditions required for some action. It is currently highly experimental and syntax/semantics are subject to change.

Use Cases and Examples

For example, the following cryptoscript function can be used to control access to a resource based on the ownership of an arbitrary Non-Fungible Token (NFT) and countersigned capability:

define only_nft_owner(nft_addr, nft_idx) {
    let n = nft.resolve(nft_addr, nft_idx);
    n.push_owner_address;
    push_countersigner_address;
    assert_equal;
}

The following cryptoscript block is used for authentication that employment, department, and access level represented as a W3C Verifiable Credential is sufficient to proceed with an action.

let vp = pop<vc::W3CVerifiablePresentation>;
push_countersigner_address;
push vp.signer;
assert_equal;
let vc = vp.vc[0];
assert_elem vc.issuer [
    did:pkh:eip155:0xb9c5714089478a327f09197987f16f9e5d936e8a,
    did:ion:EiD3DIbDgBCajj2zCkE48x74FKTV9_Dcu1u_imzZddDKfg,
    did:web:credentials.corp.com,
];
assert_equal vc.department<str> "engineering";
assert_gte vc.access_level<uint64> 2;

cryptoscript can be mixed and matched. Scope and closures can be used to further refine constrainted environments with attenuated permissions, similar to the use of chroot in UNIX. It can also be used to explicit implement a verification method, including the set of cryptographic operations against data, to ensure there is no ambiguity in contrast to specifying a data model alone.

Design Goals

• Simplicity. Towards writing secure software, it's useful to reduce any unnecessary complexity. This results in a smaller implementation and attack surface area.
• Human-readability. Code-literate humans should be able to make sense of cryptoscript without much effort for ease of debug and review.
• Extensibility. Other systems will need to be integrated to maximize utility across a variety of environments, including the reading of blockchain data across different blockchain architectures, W3C Verifiable Credentials, X.509 infrastructure, the variety of cryptosystems supported across different DID methods, in-production systems such as SAML2 and OIDC, JWTs, macaroons, biscuits, and more.
• Composability. Although cryptosript is meant to be non-turing complete, it should still incorporate advanced language features to improve the semantics of the language to prevent errors and lower attack surface area. Sophisticated type systems that do not get in the way should be incorporated to prevent entire classes of errors. Closures and S-expressions might be used to reduce permissioning scope, and a delegated capability could be implemented as a signed outer codeblock with bring-your-own-block semantics for custom functionality with attenuated permissions.

Use with Capabilities

Due to the vast scale and variety of user data, we cannot specify all possible permissions upfront with traditional approaches like RBAC. Capability-based permission models are far more flexible and work like a hall pass. Users can define new custom permissions with cryptoscript, and authorize with their keys.

There are infinite permutations of the possible ways to permission access with on-chain and off-chain data, impossible to specify a priori. We introduce a non-turing complete DSL inspired by bitcoin script called cryptoscript, where the presenter "clears" a puzzle to get authorized. cryptoscript is extensible with modules to support all blockchain networks and off-chain data. This policy-as-code primitive can create infinite matching representations.

Demo

There are two demos:

• Local: this demo is self-contained to not require any API keys
• Etherscan: this demo requires a free Etherscan API key, which you can get here

Local Demo

The local demo requires running a tiny test server, which can be started with the following command:

cargo run --bin rest-api

Note: this API accepts PUT's of new GET "API's" for testing: each requires a fixed application/json request body and returns a fixed application/json response.

To run the demo itself, run:

cargo r --bin cryptoscript -- \
  --code examples/local_demo_code.json \
  --cache-location examples/local_cache.json \
  --input examples/input.json \
  --queries examples/local_query.json \
  --variables '{
    "contractaddress": "0x57d90b64a1a57749b0f932f1a3395792e12e7055",
    "address": "0xe04f27eb70e025b78871a2ad7eabe85e61212761",
    "apikey": "DUMMY_ETHERSCAN_API_KEY" }'

You'll see successful! if it completes without any errors.

Etherscan Demo

NOTE: this demo currently ignores any errors from Etherscan.

This demo requires a free Etherscan API key, which you can get here

Once you have an API key, replace YOUR_ETHERSCAN_API_KEY below with your API key from Etherscan to run the demo:

cargo r --bin cryptoscript -- \
  --code examples/demo_code.json \
  --cache-location examples/cache.json \
  --input examples/input.json \
  --queries examples/query.json \
  --variables '{
    "contractaddress": "0x57d90b64a1a57749b0f932f1a3395792e12e7055",
    "address": "0xe04f27eb70e025b78871a2ad7eabe85e61212761",
    "apikey": "YOUR_ETHERSCAN_API_KEY" }'

Troubleshooting Demo's

If you have any issues, make sure to clear any cache.json files to ensure you're receiving fresh query responses.