Merge pull request #113 from sine-fdn/v0.2

Hide low-level type details when using `compile` + `GarbleProgram`

Author: fkettelhoit

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "garble_lang"
-version = "0.1.8"
+version = "0.2.0"
 edition = "2021"
 rust-version = "1.60.0"
 description = "Turing-Incomplete Programming Language for Multi-Party Computation with Garbled Circuits"

Cargo.toml

@@ -3,19 +3,25 @@
 use crate::{compile::wires_as_unsigned, env::Env, token::MetaInfo};
 use std::collections::HashMap;
 
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
+
 // This module currently implements a few basic kinds of circuit optimizations:
 //
 // 1. Constant evaluation (e.g. x ^ 0 == x; x & 1 == x; x & 0 == 0)
 // 2. Sub-expression sharing (wires are re-used if a gate with the same type and inputs exists)
 // 3. Pruning of useless gates (gates that are not part of the output nor used by other gates)
 
 const PRINT_OPTIMIZATION_RATIO: bool = false;
+const MAX_GATES: usize = (u32::MAX >> 4) as usize;
+const MAX_AND_GATES: usize = (u32::MAX >> 8) as usize;
 
 /// Data type to uniquely identify gates.
 pub type GateIndex = usize;
 
-/// Description of a gate executed under S-MPC.
+/// Description of a gate executed under MPC.
 #[derive(Debug, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum Gate {
     /// A logical XOR gate attached to the two specified input wires.
     Xor(GateIndex, GateIndex),
@@ -25,7 +31,7 @@ pub enum Gate {
     Not(GateIndex),
 }
 
-/// Representation of a circuit evaluated by an S-MPC engine.
+/// Representation of a circuit evaluated by an MPC engine.
 ///
 /// Each circuit consists of 3 parts:
 ///
@@ -66,6 +72,7 @@ pub enum Gate {
 /// true and constant false, specified as `Gate::Xor(0, 0)` with wire `n` and `Gate::Not(n)` (and
 /// thus depend on the first input bit for their specifications).
 #[derive(Debug, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct Circuit {
     /// The different parties, with `usize` at index `i` as the number of input bits for party `i`.
     pub input_gates: Vec<usize>,
@@ -75,7 +82,103 @@ pub struct Circuit {
     pub output_gates: Vec<GateIndex>,
 }
 
+/// An input wire or a gate operating on them.
+pub enum Wire {
+    /// An input wire, with its value coming directly from one of the parties.
+    Input(GateIndex),
+    /// A logical XOR gate attached to the two specified input wires.
+    Xor(GateIndex, GateIndex),
+    /// A logical AND gate attached to the two specified input wires.
+    And(GateIndex, GateIndex),
+    /// A logical NOT gate attached to the specified input wire.
+    Not(GateIndex),
+}
+
+/// Errors occurring during the validation or the execution of the MPC protocol.
+#[derive(Debug, PartialEq, Eq)]
+pub enum CircuitError {
+    /// The gate with the specified wire contains invalid gate connections.
+    InvalidGate(usize),
+    /// The specified output gate does not exist in the circuit.
+    InvalidOutput(usize),
+    /// The circuit does not specify any output gates.
+    EmptyOutputs,
+    /// The provided circuit has too many gates to be processed.
+    MaxCircuitSizeExceeded,
+    /// The provided index does not correspond to any party.
+    PartyIndexOutOfBounds,
+}
+
 impl Circuit {
+    /// Returns all the wires (inputs + gates) in the circuit, in ascending order.
+    pub fn wires(&self) -> Vec<Wire> {
+        let mut gates = vec![];
+        for (party, inputs) in self.input_gates.iter().enumerate() {
+            for _ in 0..*inputs {
+                gates.push(Wire::Input(party))
+            }
+        }
+        for gate in self.gates.iter() {
+            let gate = match gate {
+                Gate::Xor(x, y) => Wire::Xor(*x, *y),
+                Gate::And(x, y) => Wire::And(*x, *y),
+                Gate::Not(x) => Wire::Not(*x),
+            };
+            gates.push(gate);
+        }
+        gates
+    }
+
+    /// Returns the number of AND gates in the circuit.
+    pub fn and_gates(&self) -> usize {
+        self.gates
+            .iter()
+            .filter(|g| matches!(g, Gate::And(_, _)))
+            .count()
+    }
+
+    /// Checks that the circuit only uses valid wires, includes no cycles, has outputs, etc.
+    pub fn validate(&self) -> Result<(), CircuitError> {
+        let mut num_and_gates = 0;
+        let wires = self.wires();
+        for (i, g) in wires.iter().enumerate() {
+            match g {
+                Wire::Input(_) => {}
+                &Wire::Xor(x, y) => {
+                    if x >= i || y >= i {
+                        return Err(CircuitError::InvalidGate(i));
+                    }
+                }
+                &Wire::And(x, y) => {
+                    if x >= i || y >= i {
+                        return Err(CircuitError::InvalidGate(i));
+                    }
+                    num_and_gates += 1;
+                }
+                &Wire::Not(x) => {
+                    if x >= i {
+                        return Err(CircuitError::InvalidGate(i));
+                    }
+                }
+            }
+        }
+        if self.output_gates.is_empty() {
+            return Err(CircuitError::EmptyOutputs);
+        }
+        for &o in self.output_gates.iter() {
+            if o >= wires.len() {
+                return Err(CircuitError::InvalidOutput(o));
+            }
+        }
+        if num_and_gates > MAX_AND_GATES {
+            return Err(CircuitError::MaxCircuitSizeExceeded);
+        }
+        if wires.len() > MAX_GATES {
+            return Err(CircuitError::MaxCircuitSizeExceeded);
+        }
+        Ok(())
+    }
+
     /// Evaluates the circuit with the specified inputs (with one `Vec<bool>` per party).
     ///
     /// Assumes that the inputs have been previously type-checked and **panics** if the number of

src/circuit.rs

@@ -43,6 +43,8 @@ pub enum EvalError {
     UnexpectedNumberOfInputsFromParty(usize),
     /// An input literal could not be parsed.
     LiteralParseError(CompileTimeError),
+    /// The circuit does not have an input argument with the given index.
+    InvalidArgIndex(usize),
     /// The literal is not of the expected parameter type.
     InvalidLiteralType(Literal, Type),
     /// The number of output bits does not match the expected type.
@@ -68,6 +70,9 @@ impl std::fmt::Display for EvalError {
             EvalError::LiteralParseError(err) => {
                 err.fmt(f)
             }
+            EvalError::InvalidArgIndex(i) => {
+                f.write_fmt(format_args!("The circuit does not an input argument with index {i}"))
+            }
             EvalError::InvalidLiteralType(literal, ty) => {
                 f.write_fmt(format_args!("The argument literal is not of type {ty}: '{literal}'"))
             }

src/eval.rs

@@ -1,20 +1,59 @@
 //! A purely functional programming language with a Rust-like syntax that compiles to logic gates
 //! for secure multi-party computation.
+//!
+//! Garble programs always terminate and are compiled into a combination of boolean AND / XOR / NOT
+//! gates. These boolean circuits can either be executed directly (mostly for testing purposes) or
+//! passed to a multi-party computation engine.
+//!
+//! ```rust
+//! use garble_lang::{compile, literal::Literal, token::UnsignedNumType::U32};
+//!
+//! // Compile and type-check a simple program to add the inputs of 3 parties:
+//! let code = "pub fn main(x: u32, y: u32, z: u32) -> u32 { x + y + z }";
+//! let prg = compile(code).map_err(|e| e.prettify(&code)).unwrap();
+//!
+//! // We can evaluate the circuit directly, useful for testing purposes:
+//! let mut eval = prg.evaluator();
+//! eval.set_u32(2);
+//! eval.set_u32(10);
+//! eval.set_u32(100);
+//! let output = eval.run().map_err(|e| e.prettify(&code)).unwrap();
+//! assert_eq!(u32::try_from(output).map_err(|e| e.prettify(&code)).unwrap(), 2 + 10 + 100);
+//!
+//! // Or we can run the compiled circuit in an MPC engine, simulated using `prg.circuit.eval()`:
+//! let x = prg.parse_arg(0, "2u32").unwrap().as_bits();
+//! let y = prg.parse_arg(1, "10u32").unwrap().as_bits();
+//! let z = prg.parse_arg(2, "100u32").unwrap().as_bits();
+//! let output = prg.circuit.eval(&[x, y, z]); // use your own MPC engine here instead
+//! let result = prg.parse_output(&output).unwrap();
+//! assert_eq!("112u32", result.to_string());
+//!
+//! // Input arguments can also be constructed directly as literals:
+//! let x = prg.literal_arg(0, Literal::NumUnsigned(2, U32)).unwrap().as_bits();
+//! let y = prg.literal_arg(1, Literal::NumUnsigned(10, U32)).unwrap().as_bits();
+//! let z = prg.literal_arg(2, Literal::NumUnsigned(100, U32)).unwrap().as_bits();
+//! let output = prg.circuit.eval(&[x, y, z]); // use your own MPC engine here instead
+//! let result = prg.parse_output(&output).unwrap();
+//! assert_eq!(Literal::NumUnsigned(112, U32), result);
+//! ```
 
 #![deny(unsafe_code)]
 #![deny(missing_docs)]
 #![deny(rustdoc::broken_intra_doc_links)]
 
+use ast::{Expr, FnDef, Pattern, Program, Stmt, Type, VariantExpr};
 use check::TypeError;
+use circuit::Circuit;
 use compile::CompilerError;
-use eval::EvalError;
+use eval::{EvalError, Evaluator};
+use literal::Literal;
 use parse::ParseError;
 use scan::{scan, ScanError};
-use std::fmt::Write as _;
+use std::fmt::{Display, Write as _};
 use token::MetaInfo;
 
-use ast::{Expr, FnDef, Pattern, Program, Stmt, Type, VariantExpr};
-use circuit::Circuit;
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
 
 /// [`crate::ast::Program`] without any associated type information.
 pub type UntypedProgram = Program<()>;
@@ -56,12 +95,91 @@ pub fn check(prg: &str) -> Result<TypedProgram, Error> {
     Ok(scan(prg)?.parse()?.type_check()?)
 }
 
-/// Scans, parses, type-checks and then compiles a program to a circuit of gates.
-pub fn compile(prg: &str, fn_name: &str) -> Result<(TypedProgram, TypedFnDef, Circuit), Error> {
+/// Scans, parses, type-checks and then compiles the `"main"` fn of a program to a boolean circuit.
+pub fn compile(prg: &str) -> Result<GarbleProgram, Error> {
     let program = check(prg)?;
-    let (circuit, main_fn) = program.compile(fn_name)?;
-    let main_fn = main_fn.clone();
-    Ok((program, main_fn, circuit))
+    let (circuit, main) = program.compile("main")?;
+    let main = main.clone();
+    Ok(GarbleProgram {
+        program,
+        main,
+        circuit,
+    })
+}
+
+/// The result of type-checking and compiling a Garble program.
+#[derive(Debug, Clone)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct GarbleProgram {
+    /// The type-checked represenation of the full program.
+    pub program: TypedProgram,
+    /// The function to be executed as a circuit.
+    pub main: TypedFnDef,
+    /// The compilation output, as a circuit of boolean gates.
+    pub circuit: Circuit,
+}
+
+/// An input argument for a Garble program and circuit.
+#[derive(Debug, Clone)]
+pub struct GarbleArgument<'a>(Literal, &'a TypedProgram);
+
+impl GarbleProgram {
+    /// Returns an evaluator that can be used to run the compiled circuit.
+    pub fn evaluator(&self) -> Evaluator<'_> {
+        Evaluator::new(&self.program, &self.main, &self.circuit)
+    }
+
+    /// Type-checks and uses the literal as the circuit input argument with the given index.
+    pub fn literal_arg(
+        &self,
+        arg_index: usize,
+        literal: Literal,
+    ) -> Result<GarbleArgument<'_>, EvalError> {
+        let Some(param) = self.main.params.get(arg_index) else {
+            return Err(EvalError::InvalidArgIndex(arg_index));
+        };
+        if !literal.is_of_type(&self.program, &param.ty) {
+            return Err(EvalError::InvalidLiteralType(literal, param.ty.clone()));
+        }
+        Ok(GarbleArgument(literal, &self.program))
+    }
+
+    /// Tries to parse the string as the circuit input argument with the given index.
+    pub fn parse_arg(
+        &self,
+        arg_index: usize,
+        literal: &str,
+    ) -> Result<GarbleArgument<'_>, EvalError> {
+        let Some(param) = self.main.params.get(arg_index) else {
+            return Err(EvalError::InvalidArgIndex(arg_index));
+        };
+        let literal = Literal::parse(&self.program, &param.ty, literal)
+            .map_err(EvalError::LiteralParseError)?;
+        Ok(GarbleArgument(literal, &self.program))
+    }
+
+    /// Tries to convert the circuit output back to a Garble literal.
+    pub fn parse_output(&self, bits: &[bool]) -> Result<Literal, EvalError> {
+        Literal::from_result_bits(&self.program, &self.main.ty, bits)
+    }
+}
+
+impl GarbleArgument<'_> {
+    /// Converts the argument to input bits for the compiled circuit.
+    pub fn as_bits(&self) -> Vec<bool> {
+        self.0.as_bits(self.1)
+    }
+
+    /// Converts the argument to a Garble literal.
+    pub fn as_literal(&self) -> Literal {
+        self.0.clone()
+    }
+}
+
+impl Display for GarbleArgument<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.0.fmt(f)
+    }
 }
 
 /// Errors that can occur during compile time, while a program is scanned, parsed or type-checked.