refactor(crypto): CRP-2441 Remove EccFieldElement abstraction

rs/crypto/internal/crypto_lib/threshold_sig/tecdsa/BUILD.bazel

@@ -92,16 +92,6 @@ rust_bench(
     ],
 )
 
-rust_bench(
-    name = "field_ops_bench",
-    testonly = True,
-    srcs = ["benches/field_ops.rs"],
-    deps = [
-        ":tecdsa",
-        "@crate_index//:criterion",
-    ],
-)
-
 rust_bench(
     name = "group_ops_bench",
     testonly = True,

rs/crypto/internal/crypto_lib/threshold_sig/tecdsa/Cargo.toml

@@ -39,10 +39,6 @@ bip32 = { version = "0.5", features = ["secp256k1"] }
 num-traits = { version = "0.2.15" }
 strum = "0.25"
 
-[[bench]]
-name = "field_ops"
-harness = false
-
 [[bench]]
 name = "poly"
 harness = false

rs/crypto/internal/crypto_lib/threshold_sig/tecdsa/fe-derive/src/lib.rs

@@ -244,6 +244,9 @@ fn define_fe_struct(config: &FieldElementConfig) -> proc_macro2::TokenStream {
             const MONTY_R3: Self = Self::from_limbs([#(#monty_r3_limbs,)*]);
             const P_DASH: u64 = #p_dash;
 
+            /// Size of this field element in bytes
+            pub const BYTES: usize = 8 * #limbs;
+
             /// Initialize from limbs (private constructor)
             const fn from_limbs(limbs: [u64; #limbs]) -> Self {
                 Self { limbs }
@@ -285,11 +288,24 @@ fn define_fe_struct(config: &FieldElementConfig) -> proc_macro2::TokenStream {
                 }
             }
 
+            /// Conditional assignment matching hash2curve notation
+            ///
+            /// CMOV(a, b, c): If c is False, CMOV returns a, otherwise it returns b.
+            pub fn cmov(a: &Self, b: &Self, assign: subtle::Choice) -> Self {
+                use subtle::ConditionallySelectable;
+
+                let mut r = [0u64; #limbs];
+                for i in 0..#limbs {
+                    r[i] = u64::conditional_select(&a.limbs[i], &b.limbs[i], assign);
+                }
+                Self::from_limbs(r)
+            }
+
             /// Parse the given byte array as a field element.
             ///
             /// Return None if the byte array does not represeent an integer in [0,p)
             pub fn from_bytes(bytes: &[u8]) -> std::option::Option<Self> {
-                if bytes.len() != 8 * #limbs {
+                if bytes.len() != Self::BYTES {
                     return None;
                 }
 
@@ -316,35 +332,46 @@ fn define_fe_struct(config: &FieldElementConfig) -> proc_macro2::TokenStream {
             }
 
             pub fn from_bytes_wide(bytes: &[u8]) -> Option<Self> {
-                if bytes.len() > 2 * 8 * #limbs {
+                if bytes.len() > 2 * Self::BYTES {
                     return None;
                 }
 
-                let mut wide_bytes = [0u8; 2 * 8 * #limbs];
-                wide_bytes[2 * 8 * #limbs - bytes.len()..].copy_from_slice(bytes);
+                let mut wide_bytes = [0u8; 2 * Self::BYTES];
+                wide_bytes[2 * Self::BYTES - bytes.len()..].copy_from_slice(bytes);
 
+                Some(Self::from_bytes_wide_exact(&wide_bytes))
+            }
+
+            pub fn from_bytes_wide_exact(wide_bytes: &[u8; 2*Self::BYTES]) -> Self {
                 let mut limbs = [0u64; 2 * #limbs];
 
                 for i in 0..2 * #limbs {
                     limbs[2 * #limbs - 1 - i] = u64::from_be_bytes(wide_bytes[i * 8..(i + 1) * 8].try_into().unwrap());
                 }
 
                 // First reduce then mul by R3 to convert to Montgomery form
-                Some(Self::redc(&limbs).mul(&Self::MONTY_R3))
+                Self::redc(&limbs).mul(&Self::MONTY_R3)
             }
 
             /// Return the encoding of this field element
-            pub fn as_bytes(&self) -> [u8; 8*#limbs] {
+            pub fn as_bytes(&self) -> [u8; Self::BYTES] {
                 // Convert from Montgomery form
                 let value = Self::redc(&self.limbs);
-                let mut ret = [0u8; 8 * #limbs];
+                let mut ret = [0u8; Self::BYTES];
                 for i in 0..#limbs {
                     ret[8 * i..(8 * i + 8)]
                         .copy_from_slice(&value.limbs[#limbs - 1 - i].to_be_bytes());
                 }
                 ret
             }
 
+            /// Return the "sign" of self (effectively self mod 2)
+            ///
+            /// See Section 4.1 of RFC 9380 for details
+            pub fn sign(&self) -> u8 {
+                (self.as_bytes()[Self::BYTES - 1] & 1) as u8
+            }
+
             /// Return self + rhs mod p
             pub fn add(&self, rhs: &Self) -> Self {
                 let mut sum = [0u64; #limbs + 1];
@@ -359,10 +386,15 @@ fn define_fe_struct(config: &FieldElementConfig) -> proc_macro2::TokenStream {
             }
 
             /// Return self - rhs mod p
-            pub fn subtract(&self, rhs: &Self) -> Self {
+            pub fn sub(&self, rhs: &Self) -> Self {
                 Self::mod_sub(&self.limbs, rhs.limbs)
             }
 
+            /// Return -self mod p
+            pub fn negate(&self) -> Self {
+                Self::zero().sub(self)
+            }
+
             fn mod_sub(l: &[u64], r: [u64; #limbs]) -> Self {
                 let mut borrow = 0;
                 let mut w = [0u64; #limbs];

rs/crypto/internal/crypto_lib/threshold_sig/tecdsa/fuzz/BUILD.bazel

@@ -12,27 +12,13 @@ DEPENDENCIES = [
 
 MACRO_DEPENDENCIES = []
 
-rust_fuzz_test_binary(
-    name = "fe",
-    srcs = ["fuzz_targets/fe.rs"],
-    proc_macro_deps = MACRO_DEPENDENCIES,
-    deps = DEPENDENCIES,
-)
-
 rust_fuzz_test_binary(
     name = "scalar",
     srcs = ["fuzz_targets/scalar.rs"],
     proc_macro_deps = MACRO_DEPENDENCIES,
     deps = DEPENDENCIES,
 )
 
-rust_fuzz_test_binary(
-    name = "sqrt_ratio",
-    srcs = ["fuzz_targets/sqrt_ratio.rs"],
-    proc_macro_deps = MACRO_DEPENDENCIES,
-    deps = DEPENDENCIES,
-)
-
 rust_fuzz_test_binary(
     name = "cbor_deserialize_dealing",
     srcs = ["fuzz_targets/cbor_deserialize_dealing.rs"],

rs/crypto/internal/crypto_lib/threshold_sig/tecdsa/fuzz/Cargo.toml

@@ -23,20 +23,8 @@ path = ".."
 [workspace]
 members = ["."]
 
-[[bin]]
-name = "fe"
-path = "fuzz_targets/fe.rs"
-test = false
-doc = false
-
 [[bin]]
 name = "scalar"
 path = "fuzz_targets/scalar.rs"
 test = false
 doc = false
-
-[[bin]]
-name = "sqrt_ratio"
-path = "fuzz_targets/sqrt_ratio.rs"
-test = false
-doc = false