Simplify k generation following RFC 6979

Author: tcoratger

Cargo.lock

@@ -17,14 +17,13 @@ exclude = ["test-data/**"]
 starknet-crypto-codegen = { version = "0.3.2", path = "../starknet-crypto-codegen" }
 starknet-curve = { version = "0.4.1", path = "../starknet-curve" }
 starknet-ff = { version = "0.3.6", path = "../starknet-ff", default-features = false }
-crypto-bigint = { version = "0.5.1", default-features = false, features = ["generic-array", "zeroize"] }
-hmac = { version = "0.12.1", default-features = false }
 num-bigint = { version = "0.4.3", default-features = false }
 num-integer = { version = "0.1.45", default-features = false }
 num-traits = { version = "0.2.15", default-features = false }
-rfc6979 = { version = "0.4.0", default-features = false }
-sha2 = { version = "0.10.6", default-features = false }
-zeroize = { version = "1.6.0", default-features = false }
+rfc6979 = { version = "0.5.0-pre.3", default-features = false }
+subtle = { version = "2.5.0", default-features = false }
+sha2 = { version = "0.11.0-pre.3", default-features = false }
+hex-literal  = { version = "0.4.1", default-features = false }
 hex = { version = "0.4.3", default-features = false, optional = true }
 
 [features]
@@ -36,7 +35,6 @@ signature-display = ["dep:hex", "alloc"]
 [dev-dependencies]
 criterion = { version = "0.4.0", default-features = false }
 hex = "0.4.3"
-hex-literal = "0.4.1"
 serde = { version = "1.0.160", features = ["derive"] }
 serde_json = "1.0.96"
 

starknet-crypto/Cargo.toml

@@ -1,12 +1,7 @@
-use crypto_bigint::{ArrayEncoding, ByteArray, Integer, U256};
-use hmac::digest::Digest;
-use sha2::digest::{crypto_common::BlockSizeUser, FixedOutputReset, HashMarker};
-use zeroize::{Zeroize, Zeroizing};
-
 use crate::FieldElement;
+use hex_literal::hex;
 
-const EC_ORDER: U256 =
-    U256::from_be_hex("0800000000000010ffffffffffffffffb781126dcae7b2321e66a241adc64d2f");
+const EC_ORDER: [u8; 32] = hex!("0800000000000010ffffffffffffffffb781126dcae7b2321e66a241adc64d2f");
 
 /// Deterministically generate ephemeral scalar `k` based on RFC 6979.
 ///
@@ -20,61 +15,32 @@ pub fn generate_k(
     private_key: &FieldElement,
     seed: Option<&FieldElement>,
 ) -> FieldElement {
-    // The message hash padding as implemented in `cairo-lang` is not needed here. The hash is
-    // padded in `cairo-lang` only to make sure the lowest 4 bits won't get truncated, but here it's
-    // never getting truncated anyways.
-    let message_hash = U256::from_be_slice(&message_hash.to_bytes_be()).to_be_byte_array();
-    let private_key = U256::from_be_slice(&private_key.to_bytes_be());
-
-    let seed_bytes = match seed {
-        Some(seed) => seed.to_bytes_be(),
-        None => [0u8; 32],
-    };
+    // Convert seed to bytes
+    let seed_bytes = seed.map_or([0u8; 32], |s| s.to_bytes_be());
 
+    // Find the index of the first non-zero byte in the seed
     let mut first_non_zero_index = 32;
-    for (ind, element) in seed_bytes.iter().enumerate() {
-        if *element != 0u8 {
+    for (ind, &element) in seed_bytes.iter().enumerate() {
+        if element != 0u8 {
             first_non_zero_index = ind;
             break;
         }
     }
 
-    let k = generate_k_shifted::<sha2::Sha256, _>(
-        &private_key,
-        &EC_ORDER,
-        &message_hash,
-        &seed_bytes[first_non_zero_index..],
+    // Convert GenericArray to [u8; 32]
+    let mut k_bytes = [0u8; 32];
+    k_bytes.copy_from_slice(
+        rfc6979::generate_k::<sha2::Sha256, rfc6979::consts::U32>(
+            (&private_key.to_bytes_be()).into(),
+            &EC_ORDER.into(),
+            (&message_hash.to_bytes_be()).into(),
+            &seed_bytes[first_non_zero_index..],
+        )
+        .as_slice(),
     );
 
-    let mut buffer = [0u8; 32];
-    buffer[..].copy_from_slice(&k.to_be_byte_array()[..]);
-
-    FieldElement::from_bytes_be(&buffer).unwrap()
-}
-
-// Modified from upstream `rfc6979::generate_k` with a hard-coded right bit shift. The more
-// idiomatic way of doing this seems to be to implement `U252` which handles bit truncation
-// interally.
-// TODO: change to use upstream `generate_k` directly.
-#[inline]
-fn generate_k_shifted<D, I>(x: &I, n: &I, h: &ByteArray<I>, data: &[u8]) -> Zeroizing<I>
-where
-    D: Default + Digest + BlockSizeUser + FixedOutputReset + HashMarker,
-    I: ArrayEncoding + Integer + Zeroize,
-{
-    let mut x = x.to_be_byte_array();
-    let mut hmac_drbg = rfc6979::HmacDrbg::<D>::new(&x, h, data);
-    x.zeroize();
-
-    loop {
-        let mut bytes = ByteArray::<I>::default();
-        hmac_drbg.fill_bytes(&mut bytes);
-        let k = I::from_be_byte_array(bytes) >> 4;
-
-        if (!k.is_zero() & k.ct_lt(n)).into() {
-            return Zeroizing::new(k);
-        }
-    }
+    // Convert bytes to FieldElement
+    FieldElement::from_bytes_be(&k_bytes).unwrap()
 }
 
 #[cfg(test)]