From 309af5234b3375e1c4484af670e2bb1d9c25ab3c Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 09:34:10 +0000
Subject: [PATCH 1/9] no_std conversion

---
 Cargo.toml         | 17 +++++----
 src/lib.rs         | 90 ++--------------------------------------------
 src/private_key.rs | 17 ++++-----
 src/public_key.rs  | 46 ++++++------------------
 4 files changed, 29 insertions(+), 141 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 6e6dfb9..66aaef7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,22 +10,28 @@ repository = "https://github.com/lolo32/ed448-rust"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
-docinclude = [] # Used only for activating `doc(include="...")` on stable.
+default = ["std"]
+std = []
 
 [dependencies.lazy_static]
 version = "1.4.0"
+default-features = false
 
 [dependencies.num-bigint]
 version = "0.4.0"
+default-features = false
 
 [dependencies.num-integer]
 version = "0.1.44"
+default-features = false
 
 [dependencies.num-traits]
 version = "0.2.14"
+default-features = false
 
 [dependencies.opaque-debug]
 version = "0.3.0"
+default-features = false
 
 [dependencies.rand_core]
 version = "0.6.2"
@@ -38,18 +44,15 @@ version = "0.9.1"
 [dependencies.subtle]
 version = "2.4.0"
 default-features = false
-features = ["std"]
 
 [dev-dependencies.base64]
 version = "0.13.0"
+default-features = false
 
 [dev-dependencies.hex]
 version = "0.4.3"
 
 [dev-dependencies.rand_core]
 version = "0.6.2"
-features = ["getrandom"]
-
-[package.metadata.docs.rs]
-rustc-args = ["--cfg", "docsrs"]
-features = ["docinclude"] # Activate `docinclude` during docs.rs build.
+default-features = false
+features = ["getrandom"]
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index 93cc579..c3352ca 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,7 +14,6 @@
 
 #![cfg_attr(feature = "docinclude", feature(external_doc))]
 #![deny(
-    missing_docs,
     missing_copy_implementations,
     missing_debug_implementations,
     trivial_numeric_casts,
@@ -115,92 +114,8 @@
     clippy::module_name_repetitions
 )]
 
-//! # EdDSA implementation for ed448
-//!
-//! This is a Edwards-Curve Digital Signature Algorithm (EdDSA) for ed448 only
-//! in pure rust.
-//!
-//! # Usage
-//!
-//! There is two variants that can be combined to sign/verify:
-//!
-//! 1. [`PrivateKey::sign`](crate::PrivateKey::sign) to sign all the content
-//!    as-it and [`PrivateKey::sign_ph`](crate::PrivateKey::sign_ph) to
-//!    pre-hash the message internaly before signing it. It will be hashed
-//!    using Shake256 and the result of 64 byte will be signed/verified.
-//!    
-//!    Note: use the same variant for verifying the signature.
-//!
-//! 2. The second parameter of [`sign`](crate::PrivateKey::sign)/
-//!    [`sign_ph`](crate::PrivateKey::sign_ph) and the third of
-//!    [`verify`](crate::PublicKey::verify)/
-//!    [`verify_ph`](crate::PublicKey::verify_ph) if an optional context
-//!    of 255 byte length max.
-//!    
-//!    The context can be used to facilitate different signature over
-//!    different protocol, but it must be immuable over the protocol.
-//!    More information about this can be found at
-//!    [RFC 8032 Use of Contexts](https://tools.ietf.org/html/rfc8032#section-8.3).
-//!
-//! # Examples
-//!
-//! ## Generating a new key pair
-//!
-//! ```
-//! use rand_core::OsRng;
-//! use ed448_rust::{PrivateKey, PublicKey};
-//! let private_key = PrivateKey::new(&mut OsRng);
-//! let public_key = PublicKey::from(&private_key);
-//! ```
-//!
-//! ## Sign a message
-//!
-//! ```
-//! # use rand_core::OsRng;
-//! use ed448_rust::{PrivateKey, Ed448Error};
-//! # let retrieve_pkey = || PrivateKey::new(&mut OsRng);
-//! let message = b"Message to sign";
-//! let private_key = retrieve_pkey();
-//! match private_key.sign(message, None) {
-//!     Ok(signature) => {
-//!         // Signature OK, use it
-//!         // This is a slice of 144 byte length
-//!     }
-//!     Err(Ed448Error::ContextTooLong) => {
-//!         // The used context is more than 255 bytes length
-//!     }
-//!     Err(_) => unreachable!()
-//! }
-//! ```
-//!
-//! ## Verify a signature
-//!
-//! ```
-//! # use rand_core::OsRng;
-//! use ed448_rust::{PublicKey, Ed448Error};
-//! # let private_key = ed448_rust::PrivateKey::new(&mut OsRng);
-//! let message = b"Signed message to verify";
-//! # let retrieve_signature = || private_key.sign(message, None).unwrap();
-//! # let retrieve_pubkey = || PublicKey::from(&private_key);
-//! let public_key = retrieve_pubkey(); // A slice or array of KEY_LENGTH byte length
-//! let signature = retrieve_signature(); // A slice or array of SIG_LENGTH byte length
-//! match public_key.verify(message, &signature, None) {
-//!     Ok(()) => {
-//!         // Signature OK, use the message
-//!     }
-//!     Err(Ed448Error::InvalidSignature) => {
-//!         // The verification of the signature is invalid
-//!     }
-//!     Err(Ed448Error::ContextTooLong) => {
-//!         // The used context is more than 255 bytes length
-//!     }
-//!     Err(Ed448Error::WrongSignatureLength) => {
-//!         // The signature is not 144 bytes length
-//!     }
-//!     Err(_) => unreachable!()
-//! }
-//! ```
-
+extern crate alloc;
+use alloc::{vec::Vec, boxed::Box, borrow::Cow};
 use sha3::{
     digest::{ExtendableOutput, Update},
     Shake256,
@@ -210,7 +125,6 @@ pub use crate::error::Ed448Error;
 
 pub use private_key::PrivateKey;
 pub use public_key::PublicKey;
-use std::borrow::Cow;
 
 mod error;
 mod point;
diff --git a/src/private_key.rs b/src/private_key.rs
index 5e2b238..fdc61e0 100644
--- a/src/private_key.rs
+++ b/src/private_key.rs
@@ -14,7 +14,9 @@
 
 use core::convert::{TryFrom, TryInto};
 
+use alloc::vec;
 use num_bigint::{BigInt, Sign};
+#[cfg(feature = "std")]
 use rand_core::{CryptoRng, RngCore};
 use sha3::{
     digest::{ExtendableOutput, Update},
@@ -48,6 +50,8 @@ impl PrivateKey {
     /// use ed448_rust::PrivateKey;
     /// let private_key = PrivateKey::new(&mut OsRng);
     /// ```
+    
+    #[cfg(feature = "std")]
     pub fn new<T>(rnd: &mut T) -> Self
     where
         T: CryptoRng + RngCore,
@@ -57,16 +61,6 @@ impl PrivateKey {
         Self::from(key)
     }
 
-    /// Convert the private key to a format exportable.
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// # use rand_core::OsRng;
-    /// # use ed448_rust::PrivateKey;
-    /// # let private_key = PrivateKey::new(&mut OsRng);
-    /// let exportable_pkey = private_key.as_bytes();
-    /// ```
     #[inline]
     #[must_use]
     pub const fn as_bytes(&self) -> &[u8; KEY_LENGTH] {
@@ -230,8 +224,10 @@ impl From<&'_ PrivateKeyRaw> for PrivateKey {
 #[cfg(test)]
 mod tests {
     use super::*;
+    #[cfg(feature = "std")]
     use rand_core::OsRng;
 
+    #[cfg(feature = "std")]
     #[test]
     fn create_new_pkey() {
         let pkey = PrivateKey::new(&mut OsRng);
@@ -245,6 +241,7 @@ mod tests {
         assert_eq!(invalid_pk.unwrap_err(), Ed448Error::WrongKeyLength);
     }
 
+    #[cfg(feature = "std")]
     #[test]
     fn invalid_context_length() {
         let pkey = PrivateKey::new(&mut OsRng);
diff --git a/src/public_key.rs b/src/public_key.rs
index edcb866..7a9b2f7 100644
--- a/src/public_key.rs
+++ b/src/public_key.rs
@@ -14,6 +14,7 @@
 
 use core::convert::TryFrom;
 
+use alloc::vec;
 use num_bigint::{BigInt, Sign};
 
 use crate::{
@@ -40,42 +41,6 @@ impl PublicKey {
         self.0.encode()
     }
 
-    /// Verify signature with public key.
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// # use rand_core::OsRng;
-    /// use ed448_rust::{PublicKey, Ed448Error};
-    /// # let private_key = ed448_rust::PrivateKey::new(&mut OsRng);
-    /// let message = b"Signed message to verify";
-    /// # let retrieve_signature = || private_key.sign(message, None).unwrap();
-    /// # let retrieve_pubkey = || PublicKey::from(&private_key);
-    /// let public_key = retrieve_pubkey();
-    /// let signature = retrieve_signature();
-    /// match public_key.verify(message, &signature, None) {
-    ///     Ok(()) => {
-    ///         // Signature OK, use the message
-    ///     }
-    ///     Err(Ed448Error::InvalidSignature) => {
-    ///         // The verification of the signature is invalid
-    ///     }
-    ///     Err(Ed448Error::ContextTooLong) => {
-    ///         // The used context is more than 255 bytes length
-    ///     }
-    ///     Err(Ed448Error::WrongSignatureLength) => {
-    ///         // The signature is not 144 bytes length
-    ///     }
-    ///     Err(_) => unreachable!()
-    /// }
-    /// ```
-    ///
-    /// # Errors
-    ///
-    /// * [`Ed448Error::InvalidSignature`] if the signature is not valid, either the public key
-    ///   or the signature used are not the right, or the message has been altered.
-    /// * [`Ed448Error::ContextTooLong`] if the optional context is more than 255 byte length.
-    /// * [`Ed448Error::WrongSignatureLength`] if the signature is not `SIG_LENGTH` byte.
     #[inline]
     pub fn verify(&self, msg: &[u8], sign: &[u8], ctx: Option<&[u8]>) -> crate::Result<()> {
         self.verify_real(msg, sign, ctx, PreHash::False)
@@ -189,9 +154,12 @@ impl TryFrom<&[u8]> for PublicKey {
 
 #[cfg(test)]
 mod tests {
+    #[cfg(feature = "std")]
     use std::convert::TryFrom;
 
     use super::*;
+    
+    #[cfg(feature = "std")]
     use rand_core::OsRng;
 
     #[test]
@@ -213,6 +181,7 @@ mod tests {
         assert_eq!(&public.as_byte()[..], &ref_public[..]);
     }
 
+    #[cfg(feature = "std")]
     #[test]
     fn wrong_verification_with_another_pub_key() {
         let secret_1 = PrivateKey::new(&mut OsRng);
@@ -231,6 +200,7 @@ mod tests {
         assert_eq!(pub_key.unwrap_err(), Ed448Error::WrongPublicKeyLength);
     }
 
+    #[cfg(feature = "std")]
     #[test]
     fn wrong_sign_length() {
         let pubkey = PublicKey::from(&PrivateKey::new(&mut OsRng));
@@ -241,6 +211,7 @@ mod tests {
         );
     }
 
+    #[cfg(feature = "std")]
     #[test]
     fn instantiate_pubkey() {
         let pkey = PrivateKey::new(&mut OsRng);
@@ -251,6 +222,7 @@ mod tests {
         assert_eq!(pub_key1.as_byte(), pub_key2.as_byte());
     }
 
+    #[cfg(feature = "std")]
     #[test]
     fn wrong_with_altered_message() {
         let secret = PrivateKey::new(&mut OsRng);
@@ -265,6 +237,7 @@ mod tests {
         );
     }
 
+    #[cfg(feature = "std")]
     #[test]
     fn wrong_with_forged_pub_key() {
         let secret = PrivateKey::new(&mut OsRng);
@@ -278,6 +251,7 @@ mod tests {
         );
     }
 
+    #[cfg(feature = "std")]
     #[test]
     fn wrong_with_forged_signature() {
         let secret = PrivateKey::new(&mut OsRng);

From 21d2b766712a11f65cb679f6b805feadf5a49e27 Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 09:55:41 +0000
Subject: [PATCH 2/9] serde support

---
 Cargo.toml        | 4 ++++
 src/point.rs      | 5 +++--
 src/public_key.rs | 5 +++--
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 66aaef7..df42e28 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,6 +9,9 @@ repository = "https://github.com/lolo32/ed448-rust"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[dependencies]
+serde = { version = "1.0", default-features = false, features = ["derive"] }
+
 [features]
 default = ["std"]
 std = []
@@ -20,6 +23,7 @@ default-features = false
 [dependencies.num-bigint]
 version = "0.4.0"
 default-features = false
+features = ["serde"]
 
 [dependencies.num-integer]
 version = "0.1.44"
diff --git a/src/point.rs b/src/point.rs
index e952fe7..74a73be 100644
--- a/src/point.rs
+++ b/src/point.rs
@@ -20,6 +20,7 @@ use core::{
 use lazy_static::lazy_static;
 use num_bigint::{BigInt, Sign};
 use num_traits::{One, Zero};
+use serde::{Serialize, Deserialize};
 
 use crate::{Ed448Error, KEY_LENGTH};
 use subtle::{Choice, ConstantTimeEq};
@@ -60,7 +61,7 @@ lazy_static! {
     );
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Field(BigInt);
 
 impl Field {
@@ -248,7 +249,7 @@ impl Div<&'_ Field> for &'_ Field {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Point {
     x: Field,
     y: Field,
diff --git a/src/public_key.rs b/src/public_key.rs
index 7a9b2f7..3b443be 100644
--- a/src/public_key.rs
+++ b/src/public_key.rs
@@ -16,6 +16,7 @@ use core::convert::TryFrom;
 
 use alloc::vec;
 use num_bigint::{BigInt, Sign};
+use serde::{Serialize, Deserialize};
 
 use crate::{
     init_sig,
@@ -27,7 +28,7 @@ use crate::{
 /// This is a public key. _Should be distributed._
 ///
 /// You can extract a `PublicKey` by calling [`Self::from()`].
-#[derive(Clone)]
+#[derive(Clone, Serialize, Deserialize)]
 pub struct PublicKey(Point);
 
 opaque_debug::implement!(PublicKey);
@@ -158,7 +159,7 @@ mod tests {
     use std::convert::TryFrom;
 
     use super::*;
-    
+
     #[cfg(feature = "std")]
     use rand_core::OsRng;
 

From afca8dde7c42946d1e7f50ca30a53ef970b8837e Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 11:03:27 +0000
Subject: [PATCH 3/9] no_std

---
 src/lib.rs        | 2 ++
 src/public_key.rs | 3 ---
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index c3352ca..237feaf 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,5 @@
+#![no_std]
+
 // Copyright 2021 Lolo_32
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
diff --git a/src/public_key.rs b/src/public_key.rs
index 3b443be..ac4f15f 100644
--- a/src/public_key.rs
+++ b/src/public_key.rs
@@ -155,9 +155,6 @@ impl TryFrom<&[u8]> for PublicKey {
 
 #[cfg(test)]
 mod tests {
-    #[cfg(feature = "std")]
-    use std::convert::TryFrom;
-
     use super::*;
 
     #[cfg(feature = "std")]

From 5929669712d30bcbd6792df6c569992c6e34053b Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 12:26:42 +0000
Subject: [PATCH 4/9] sha no_std conversion

---
 Cargo.toml         |  1 +
 src/lib.rs         | 12 +++++++++---
 src/private_key.rs |  8 ++++----
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index df42e28..d477ea2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -44,6 +44,7 @@ features = ["alloc"]
 
 [dependencies.sha3]
 version = "0.9.1"
+default-features = false
 
 [dependencies.subtle]
 version = "2.4.0"
diff --git a/src/lib.rs b/src/lib.rs
index 237feaf..6a063a8 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -119,8 +119,9 @@
 extern crate alloc;
 use alloc::{vec::Vec, boxed::Box, borrow::Cow};
 use sha3::{
-    digest::{ExtendableOutput, Update},
+    digest::{ExtendableOutput, Update, XofReader},
     Shake256,
+    Sha3_256
 };
 
 pub use crate::error::Ed448Error;
@@ -179,7 +180,9 @@ fn shake256(items: Vec<&[u8]>, ctx: &[u8], pre_hash: PreHash) -> Box<[u8]> {
     for item in items {
         shake.update(item);
     }
-    shake.finalize_boxed(114)
+    let mut h = [0_u8; 114];
+    shake.finalize_xof().read(&mut h);
+    Box::new(h)
 }
 
 /// Common tasks for signing/verifying
@@ -198,7 +201,10 @@ fn init_sig<'a, 'b>(
     let msg = match pre_hash {
         PreHash::False => Cow::Borrowed(msg),
         PreHash::True => {
-            let hash = Shake256::default().chain(msg).finalize_boxed(64).to_vec();
+            let mut h = [0_u8; 64];
+            Shake256::default().chain(msg).finalize_xof().read(&mut h);
+
+            let hash = h.to_vec();
             Cow::Owned(hash)
         }
     };
diff --git a/src/private_key.rs b/src/private_key.rs
index fdc61e0..5b01606 100644
--- a/src/private_key.rs
+++ b/src/private_key.rs
@@ -19,7 +19,7 @@ use num_bigint::{BigInt, Sign};
 #[cfg(feature = "std")]
 use rand_core::{CryptoRng, RngCore};
 use sha3::{
-    digest::{ExtendableOutput, Update},
+    digest::{ExtendableOutput, Update, XofReader},
     Shake256,
 };
 
@@ -70,9 +70,9 @@ impl PrivateKey {
     pub(crate) fn expand(&self) -> (PrivateKeyRaw, SeedRaw) {
         // 1.  Hash the 57-byte private key using SHAKE256(x, 114), storing the
         //     digest in a 114-octet large buffer, denoted h.
-        let h = Shake256::default()
-            .chain(self.as_bytes())
-            .finalize_boxed(114);
+        let mut h = [0_u8; 114];
+        Shake256::default()
+            .chain(self.as_bytes()).finalize_xof().read(&mut h);
         //     Only the lower 57 bytes are used for generating the public key.
         let mut s: [u8; KEY_LENGTH] = h[..KEY_LENGTH].try_into().unwrap();
 

From 598e153d72af2795db7f24cd657ff109bd9af1b7 Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 12:33:58 +0000
Subject: [PATCH 5/9] lazy_static no_std

---
 Cargo.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Cargo.toml b/Cargo.toml
index d477ea2..50a6109 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,7 +18,7 @@ std = []
 
 [dependencies.lazy_static]
 version = "1.4.0"
-default-features = false
+features = ["spin_no_std"]
 
 [dependencies.num-bigint]
 version = "0.4.0"

From ab912df08a9b14f4fbda0f91e05e2e98d300e8ee Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 13:21:46 +0000
Subject: [PATCH 6/9] reexport Point

---
 src/lib.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/lib.rs b/src/lib.rs
index 6a063a8..3129c26 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -121,13 +121,13 @@ use alloc::{vec::Vec, boxed::Box, borrow::Cow};
 use sha3::{
     digest::{ExtendableOutput, Update, XofReader},
     Shake256,
-    Sha3_256
 };
 
 pub use crate::error::Ed448Error;
 
 pub use private_key::PrivateKey;
 pub use public_key::PublicKey;
+pub use point::Point;
 
 mod error;
 mod point;

From 9a3db15ee7e5e489747e36b2d097135536ed34e7 Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 13:26:23 +0000
Subject: [PATCH 7/9] pubkey from byte

---
 src/public_key.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/public_key.rs b/src/public_key.rs
index ac4f15f..6c91c3c 100644
--- a/src/public_key.rs
+++ b/src/public_key.rs
@@ -42,6 +42,13 @@ impl PublicKey {
         self.0.encode()
     }
 
+    #[inline]
+    #[must_use]
+    pub fn from_byte(s: [u8; 57]) -> Result<Self, Ed448Error> {
+        // 4.  The public key A is the encoding of the point [s]B.
+        Ok(Self(Point::decode(&s)?))
+    }
+
     #[inline]
     pub fn verify(&self, msg: &[u8], sign: &[u8], ctx: Option<&[u8]>) -> crate::Result<()> {
         self.verify_real(msg, sign, ctx, PreHash::False)

From ce7393da5caecbf8f82c01b5455130bebc6de558 Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 13:27:22 +0000
Subject: [PATCH 8/9] pubkey from byte

---
 src/public_key.rs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/public_key.rs b/src/public_key.rs
index 6c91c3c..8313458 100644
--- a/src/public_key.rs
+++ b/src/public_key.rs
@@ -45,7 +45,6 @@ impl PublicKey {
     #[inline]
     #[must_use]
     pub fn from_byte(s: [u8; 57]) -> Result<Self, Ed448Error> {
-        // 4.  The public key A is the encoding of the point [s]B.
         Ok(Self(Point::decode(&s)?))
     }
 

From 4f99146232431bcd4fe2041a06344dbd85f11c0a Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Thu, 31 Aug 2023 14:58:48 +0000
Subject: [PATCH 9/9] modulus extracted to lasy_static

---
 src/point.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/point.rs b/src/point.rs
index 74a73be..7541eb1 100644
--- a/src/point.rs
+++ b/src/point.rs
@@ -28,6 +28,7 @@ use subtle::{Choice, ConstantTimeEq};
 lazy_static! {
     // 2 ^ 448 - 2 ^224 - 1
     static ref p: BigInt = BigInt::from(2).pow(448).sub(BigInt::from(2).pow(224)) - 1;
+    static ref m: BigInt = BigInt::from(2).pow(455);
     static ref d: Field = Field::new(BigInt::from(-39081));
     static ref f0: Field = Field::new(BigInt::zero());
     static ref f1: Field = Field::new(BigInt::one());
@@ -335,7 +336,7 @@ impl Point {
 
     /// Unserialize number from bits.
     fn frombytes(x: &[u8]) -> crate::Result<Field> {
-        let rv = BigInt::from_bytes_le(Sign::Plus, x) % BigInt::from(2).pow(455);
+        let rv = BigInt::from_bytes_le(Sign::Plus, x) % &m as &BigInt;
         if &rv < &p as &BigInt {
             Ok(Field::new(rv))
         } else {