feat: add cross contract call to Solidity verifier example

cross-contract-calls-solidity-verifiers/.gitignore

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+# Dependencies
+node_modules/
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# Environment variables
+.env
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+# Build outputs
+circuits/target/
+circuits/proofs/
+contracts/artifacts/
+contracts/cache/
+frontend/build/
+frontend/dist/
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Logs
+*.log
+logs/
+
+# Temporary files
+*.tmp
+*.temp
+
+
+Prover.toml
+Verifier.toml
+*.wasm
+*.vk
+*.pk
+*.proof

cross-contract-calls-solidity-verifiers/README.md

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+# Anonymous ZK Poll App
+
+This project demonstrates an anonymous polling application leveraging Zero-Knowledge (ZK) proofs to ensure unique participation without revealing user identities. It utilizes Noir for ZK circuit development.
+
+## Features (Planned)
+
+- Anonymous Voting: Users can cast votes without revealing their identity.
+
+- Unique Participation: ZK proofs prevent double-voting.
+
+- Real-time Results: Poll results are updated in real-time.
+
+- Scalable Architecture: Designed with clear separation of concerns for future expansion.

cross-contract-calls-solidity-verifiers/circuits/Nargo.toml

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+[package]
+name = "circuits"
+type = "bin"
+authors = [""]
+
+[dependencies]
+
+# Configuration for the circuit
+[circuit]
+# Maximum number of constraints (adjust based on your needs)
+max_constraints = 100000
+
+# Backend configuration
+[backend]
+# Use Barretenberg backend (default)
+backend = "barretenberg"
+
+# Optimization settings
+[optimization]
+# Enable optimizations for smaller proof size
+optimize_for_size = true
+
+# Enable parallel proving (if supported)
+enable_parallel = true

cross-contract-calls-solidity-verifiers/circuits/src/main.nr

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+use dep::std;
+
+global MERKLE_TREE_DEPTH: u32 = 20;
+
+fn main(user_secret: Field,
+    vote_choice: Field,
+    merkle_path: [Field; MERKLE_TREE_DEPTH],
+    merkle_indices: [u1; MERKLE_TREE_DEPTH],
+    merkle_root: pub Field,
+    nullifier: pub Field,
+    poll_id: pub Field,
+    max_options: pub Field
+) {
+    assert((vote_choice as u32) < (max_options as u32));
+    assert((vote_choice as u32) >= 0);
+
+    // verify that the nullifier is correctly computed
+    let computed_nullifier = std::hash::pedersen_hash([user_secret, poll_id]);
+    // std::println(f"Computed nullifier: {computed_nullifier}");
+    assert(nullifier == computed_nullifier);
+
+    // Verify that the user is in the eligible voters merkle tree
+    let leaf = std::hash::pedersen_hash([user_secret]);
+    // std::println(f"Leaf hash: {leaf}");
+    let is_valid_member = verify_merkle_membership(
+        leaf,
+        merkle_root,
+        merkle_path,
+        merkle_indices
+    );
+    assert(is_valid_member);
+
+    // ensure user_secret is not 0
+    assert(user_secret != 0);
+
+    std::println(f"Vote verified for poll {poll_id}");
+}
+
+fn verify_merkle_membership(
+    leaf: Field,
+    root: Field,
+    path: [Field; MERKLE_TREE_DEPTH],
+    indices: [u1; MERKLE_TREE_DEPTH]
+) -> bool {
+    let mut current = leaf;
+
+    // std::println(f"Starting with leaf: {leaf}");
+    for i in 0..MERKLE_TREE_DEPTH {
+        let path_element = path[i];
+        // std::println(f"Step {i}: current = {current}, path_element = {path_element}");
+        let is_right = indices[i];
+
+        if is_right == 0 {
+            // Current is left child
+            current = std::hash::pedersen_hash([current, path_element]);
+        } else {
+            // Current is right child
+            current = std::hash::pedersen_hash([path_element, current]);
+        }
+    }
+    // std::println(f"Final computed root: {current}");
+    current == root
+}

cross-contract-calls-solidity-verifiers/ink-contract/.gitignore

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+# Ignore build artifacts from the local tests sub-crate.
+/target/
+
+# Ignore backup files creates by cargo fmt.
+**/*.rs.bk
+
+# Remove Cargo.lock when creating an executable, leave it for libraries
+# More information here http://doc.crates.io/guide.html#cargotoml-vs-cargolock
+Cargo.lock

cross-contract-calls-solidity-verifiers/ink-contract/Cargo.toml

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+[package]
+name = "contracts"
+version = "0.1.0"
+authors = ["[your_name] <[your_email]>"]
+edition = "2021"
+
+[dependencies]
+const-crypto = "0.3.0"
+ink = { version = "6.0.0-beta", default-features = false, features = ["unstable-hostfn"] }
+scale-info = { version = "2.11.6", default-features = false, features = ["derive"] }
+
+[dev-dependencies]
+ink_e2e = "6.0.0-beta"
+
+[lib]
+path = "lib.rs"
+
+[features]
+default = ["std"]
+std = [
+    "ink/std",
+    "scale-info/std",
+]
+ink-as-dependency = []
+e2e-tests = []
+
+[package.metadata.ink-lang]
+abi = "all"
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = [
+    'cfg(ink_abi, values("ink", "sol", "all"))'
+]