Blake PRF & R1CS Boolean Refactor (#132)

* refactor(r1cs-std/boolean): expose enforcing value less than functionality

* fix(r1cs-std/boolean): ensure num_bits is calculated correctly from the arg

* feat(primitives/blake2s): allow creating Blake2s with custom params

crypto-primitives/src/prf/blake2s/constraints.rs

@@ -313,20 +313,50 @@ fn blake2s_compression<ConstraintF: PrimeField, CS: ConstraintSystem<ConstraintF
 //
 
 pub fn blake2s_gadget<ConstraintF: PrimeField, CS: ConstraintSystem<ConstraintF>>(
+    cs: CS,
+    input: &[Boolean],
+) -> Result<Vec<UInt32>, SynthesisError> {
+    assert!(input.len() % 8 == 0);
+    let mut parameters = [0; 8];
+    parameters[0] = 0x01010000 ^ 32;
+    blake2s_gadget_with_parameters(cs, input, &parameters)
+}
+
+pub fn blake2s_gadget_with_parameters<
+    ConstraintF: PrimeField,
+    CS: ConstraintSystem<ConstraintF>,
+>(
     mut cs: CS,
     input: &[Boolean],
+    parameters: &[u32; 8],
 ) -> Result<Vec<UInt32>, SynthesisError> {
     assert!(input.len() % 8 == 0);
 
     let mut h = Vec::with_capacity(8);
-    h.push(UInt32::constant(0x6A09E667 ^ 0x01010000 ^ 32));
-    h.push(UInt32::constant(0xBB67AE85));
-    h.push(UInt32::constant(0x3C6EF372));
-    h.push(UInt32::constant(0xA54FF53A));
-    h.push(UInt32::constant(0x510E527F));
-    h.push(UInt32::constant(0x9B05688C));
-    h.push(UInt32::constant(0x1F83D9AB));
-    h.push(UInt32::constant(0x5BE0CD19));
+    h.push(
+        UInt32::constant(0x6A09E667).xor(cs.ns(|| "xor h[0]"), &UInt32::constant(parameters[0]))?,
+    );
+    h.push(
+        UInt32::constant(0xBB67AE85).xor(cs.ns(|| "xor h[1]"), &UInt32::constant(parameters[1]))?,
+    );
+    h.push(
+        UInt32::constant(0x3C6EF372).xor(cs.ns(|| "xor h[2]"), &UInt32::constant(parameters[2]))?,
+    );
+    h.push(
+        UInt32::constant(0xA54FF53A).xor(cs.ns(|| "xor h[3]"), &UInt32::constant(parameters[3]))?,
+    );
+    h.push(
+        UInt32::constant(0x510E527F).xor(cs.ns(|| "xor h[4]"), &UInt32::constant(parameters[4]))?,
+    );
+    h.push(
+        UInt32::constant(0x9B05688C).xor(cs.ns(|| "xor h[5]"), &UInt32::constant(parameters[5]))?,
+    );
+    h.push(
+        UInt32::constant(0x1F83D9AB).xor(cs.ns(|| "xor h[6]"), &UInt32::constant(parameters[6]))?,
+    );
+    h.push(
+        UInt32::constant(0x5BE0CD19).xor(cs.ns(|| "xor h[7]"), &UInt32::constant(parameters[7]))?,
+    );
 
     let mut blocks: Vec<Vec<UInt32>> = vec![];
 

crypto-primitives/src/prf/blake2s/mod.rs

@@ -1,3 +1,4 @@
+use alloc::vec::Vec;
 use blake2::Blake2s as b2s;
 use digest::Digest;
 
@@ -26,3 +27,63 @@ impl PRF for Blake2s {
         Ok(result)
     }
 }
+
+#[derive(Clone)]
+pub struct Blake2sWithParameterBlock {
+    pub digest_length:     u8,
+    pub key_length:        u8,
+    pub fan_out:           u8,
+    pub depth:             u8,
+    pub leaf_length:       u32,
+    pub node_offset:       u32,
+    pub xof_digest_length: u16,
+    pub node_depth:        u8,
+    pub inner_length:      u8,
+    pub salt:              [u8; 8],
+    pub personalization:   [u8; 8],
+}
+
+impl Blake2sWithParameterBlock {
+    pub fn parameters(&self) -> [u32; 8] {
+        let mut parameters = [0; 8];
+        parameters[0] = u32::from_le_bytes([
+            self.digest_length,
+            self.key_length,
+            self.fan_out,
+            self.depth,
+        ]);
+        parameters[1] = self.leaf_length;
+        parameters[2] = self.node_offset;
+        parameters[3] = u32::from_le_bytes([
+            self.xof_digest_length as u8,
+            (self.xof_digest_length >> 8) as u8,
+            self.node_depth,
+            self.inner_length,
+        ]);
+
+        let mut salt_bytes_1 = [0; 4];
+        let mut salt_bytes_2 = [0; 4];
+        let mut personalization_bytes_1 = [0; 4];
+        let mut personalization_bytes_2 = [0; 4];
+        for i in 0..4 {
+            salt_bytes_1[i] = self.salt[i];
+            salt_bytes_2[i] = self.salt[4 + i];
+            personalization_bytes_1[i] = self.personalization[i];
+            personalization_bytes_2[i] = self.personalization[4 + i];
+        }
+        parameters[4] = u32::from_le_bytes(salt_bytes_1);
+        parameters[5] = u32::from_le_bytes(salt_bytes_2);
+        parameters[6] = u32::from_le_bytes(personalization_bytes_1);
+        parameters[7] = u32::from_le_bytes(personalization_bytes_2);
+
+        parameters
+    }
+
+    pub fn evaluate(&self, input: &[u8]) -> Vec<u8> {
+        let eval_time = start_timer!(|| "Blake2sWithParameterBlock::Eval");
+        let mut h = b2s::with_parameter_block(&self.parameters());
+        h.input(input.as_ref());
+        end_timer!(eval_time);
+        h.result().to_vec()
+    }
+}

r1cs-std/src/bits/boolean.rs

@@ -1,4 +1,4 @@
-use algebra::{BitIterator, Field, FpParameters, PrimeField};
+use algebra::{BitIterator, Field, PrimeField};
 
 use crate::{prelude::*, Assignment, Vec};
 use core::borrow::Borrow;
@@ -576,19 +576,40 @@ impl Boolean {
     /// Asserts that this bit_gadget representation is "in
     /// the field" when interpreted in big endian.
     pub fn enforce_in_field<ConstraintF, CS, F: PrimeField>(
-        mut cs: CS,
+        cs: CS,
         bits: &[Self],
     ) -> Result<(), SynthesisError>
     where
         ConstraintF: Field,
         CS: ConstraintSystem<ConstraintF>,
     {
-        let mut bits_iter = bits.iter();
-
         // b = char() - 1
         let mut b = F::characteristic().to_vec();
         assert_eq!(b[0] % 2, 1);
         b[0] -= 1;
+        let run = Self::enforce_smaller_or_equal_than::<_, _, F, _>(cs, bits, b)?;
+
+        // We should always end in a "run" of zeros, because
+        // the characteristic is an odd prime. So, this should
+        // be empty.
+        assert!(run.is_empty());
+
+        Ok(())
+    }
+
+    /// Asserts that this bit_gadget representation is smaller
+    /// or equal than the provided element
+    pub fn enforce_smaller_or_equal_than<ConstraintF, CS, F: PrimeField, E: AsRef<[u64]>>(
+        mut cs: CS,
+        bits: &[Self],
+        element: E,
+    ) -> Result<Vec<Boolean>, SynthesisError>
+    where
+        ConstraintF: Field,
+        CS: ConstraintSystem<ConstraintF>,
+    {
+        let mut bits_iter = bits.iter();
+        let b: &[u64] = element.as_ref();
 
         // Runs of ones in r
         let mut last_run = Boolean::constant(true);
@@ -598,7 +619,23 @@ impl Boolean {
         let mut run_i = 0;
         let mut nand_i = 0;
 
-        let char_num_bits = <F as PrimeField>::Params::MODULUS_BITS as usize;
+        let char_num_bits = {
+            let mut leading_zeros = 0;
+            let mut total_bits = 0;
+            let mut found_one = false;
+            for b in BitIterator::new(b.clone()) {
+                total_bits += 1;
+                if !b && !found_one {
+                    leading_zeros += 1
+                }
+                if b {
+                    found_one = true;
+                }
+            }
+
+            total_bits - leading_zeros
+        };
+
         if bits.len() > char_num_bits {
             let num_extra_bits = bits.len() - char_num_bits;
             let mut or_result = Boolean::constant(false);
@@ -651,12 +688,7 @@ impl Boolean {
         }
         assert!(bits_iter.next().is_none());
 
-        // We should always end in a "run" of zeros, because
-        // the characteristic is an odd prime. So, this should
-        // be empty.
-        assert!(current_run.is_empty());
-
-        Ok(())
+        Ok(current_run)
     }
 }