generic-ec 0.5.0

//! Serde support
//!
//! ## Default serialization format
//!
//! By default, serialization format is excessive. Points are serialized without compression.
//! Points and scalars have an extra field "curve" that specifies which curve this point/scalar
//! belongs to.
//!
//! ```rust
//! # fn main() -> Result<(), serde_json::Error> {
//! use generic_ec::{Curve, Point, Scalar, curves::Secp256k1};
//! use serde::{Serialize, Deserialize};
//!
//! #[derive(Serialize, Deserialize)]
//! #[serde(bound = "")]
//! pub struct ZkProof<E: Curve> {
//!     some_point: Point<E>,
//!     some_scalar: Scalar<E>,
//! }
//!
//! let proof = ZkProof::<Secp256k1> {
//!     some_point: Point::generator().to_point(),
//!     some_scalar: Scalar::one(),
//! };
//! assert_eq!(serde_json::to_string_pretty(&proof)?, r#"{
//!   "some_point": {
//!     "curve": "secp256k1",
//!     "point": "0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8"
//!   },
//!   "some_scalar": {
//!     "curve": "secp256k1",
//!     "scalar": "0000000000000000000000000000000000000000000000000000000000000001"
//!   }
//! }"#);
//! # Ok(()) }
//! ```
//!
//! Excessive serialization format enables better security as it makes it harder to misuse the library.
//! E.g. if by some mistake you parse a point that was initially generated on another curve, you'll get
//! instant error. Without this field, behavior is uncertain and difficult to debug: point from one curve
//! can happen to be a valid point on another curve.
//!
//! ## Compact serialization format
//!
//! You may opt for compact serialization format. If you do that, points are seialized in compressed form, and
//! extra "curve" field is dropped.
//!
//! Compact serialization format can be enabled using [serde_with] crate and [`Compact`] helper struct:
//!
//! ```rust
//! # fn main() -> Result<(), serde_json::Error> {
//! use generic_ec::{Curve, Point, Scalar, curves::Secp256k1};
//! use serde::{Serialize, Deserialize};
//! use serde_with::serde_as;
//!
//! #[serde_as]
//! #[derive(Serialize, Deserialize)]
//! #[serde(bound = "")]
//! pub struct ZkProof<E: Curve> {
//!     #[serde_as(as = "generic_ec::serde::Compact")]
//!     some_point: Point<E>,
//!     #[serde_as(as = "generic_ec::serde::Compact")]
//!     some_scalar: Scalar<E>,
//! }
//!
//! let proof = ZkProof::<Secp256k1> {
//!     some_point: Point::generator().to_point(),
//!     some_scalar: Scalar::one(),
//! };
//! assert_eq!(serde_json::to_string_pretty(&proof)?, r#"{
//!   "some_point": "0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798",
//!   "some_scalar": "0000000000000000000000000000000000000000000000000000000000000001"
//! }"#);
//! # Ok(()) }
//! ```

use phantom_type::PhantomType;

use crate::core::Curve;

/// A guard type asserting that deserialized value belongs to curve `E`
///
/// It implements [serde::Serialize] and [serde::Deserialize] traits if `serde` feature is
/// enabled. When serialized, `CurveName` is converted into string containing curve name.
/// When deserialized, it parses a string and requires it to match curve name, otherwise
/// deserialization error is returned.
///
/// This structure is present even if `serde` feature is disabled.
///
/// ## Example
///
/// ```rust
/// # fn main() -> Result<(), serde_json::Error> {
/// use generic_ec::{serde::CurveName, curves::{Secp256k1, Secp256r1}};
/// use serde_json::Value;
///
/// let curve_name = CurveName::<Secp256k1>::new();
/// let value = serde_json::to_value(&curve_name)?;
/// assert_eq!(value, Value::String("secp256k1".into()));
///
/// // `value` can be deserialized back to `CurveName<Secp256k1>`
/// let _curve_name: CurveName<Secp256k1> = serde_json::from_value(value.clone())?;
///
/// // but it can't be deserialized to `CurveName<Secp256r1>`
/// let serialization_fails = serde_json::from_value::<CurveName<Secp256r1>>(value);
/// assert!(serialization_fails.is_err());
/// # Ok(()) }
/// ```
#[derive(Debug, Clone, Copy, Eq, PartialEq, PartialOrd, Ord, Hash)]
pub struct CurveName<E: Curve>(PhantomType<E>);

impl<E: Curve> CurveName<E> {
    /// Construct a `CurveName` guard
    pub fn new() -> Self {
        Self(PhantomType::new())
    }
}

impl<E: Curve> Default for CurveName<E> {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(feature = "serde")]
impl<E: Curve> serde::Serialize for CurveName<E> {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        serializer.serialize_str(E::CURVE_NAME)
    }
}

#[cfg(feature = "serde")]
impl<'de, E: Curve> serde::Deserialize<'de> for CurveName<E> {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        pub struct CurveNameVisitor<E: Curve>(PhantomType<E>);
        impl<E: Curve> serde::de::Visitor<'_> for CurveNameVisitor<E> {
            type Value = CurveName<E>;
            fn expecting(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
                write!(f, "curve {name}", name = E::CURVE_NAME)
            }
            fn visit_str<Error>(self, v: &str) -> Result<Self::Value, Error>
            where
                Error: serde::de::Error,
            {
                if v == E::CURVE_NAME {
                    Ok(CurveName::default())
                } else {
                    Err(Error::custom(optional::error_msg::ExpectedCurve {
                        expected: E::CURVE_NAME,
                        got: v,
                    }))
                }
            }
        }
        deserializer.deserialize_str(CurveNameVisitor(PhantomType::new()))
    }
}

#[cfg(feature = "serde")]
pub use optional::*;
#[cfg(feature = "serde")]
mod optional {
    use crate::{core::Curve, Point, Scalar, SecretScalar};

    use super::CurveName;

    impl<E: Curve> serde::Serialize for Point<E> {
        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            models::PointUncompressed::from(self).serialize(serializer)
        }
    }

    impl<'de, E: Curve> serde::Deserialize<'de> for Point<E> {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            models::PointUncompressed::deserialize(deserializer)?
                .try_into()
                .map_err(<D::Error as serde::de::Error>::custom)
        }
    }

    impl<E: Curve> serde::Serialize for Scalar<E> {
        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            models::ScalarUncompressed::from(self).serialize(serializer)
        }
    }

    impl<'de, E: Curve> serde::Deserialize<'de> for Scalar<E> {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            models::ScalarUncompressed::deserialize(deserializer)?
                .try_into()
                .map_err(<D::Error as serde::de::Error>::custom)
        }
    }

    impl<E: Curve> serde::Serialize for SecretScalar<E> {
        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            self.as_ref().serialize(serializer)
        }
    }

    impl<'de, E: Curve> serde::Deserialize<'de> for SecretScalar<E> {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            Ok(SecretScalar::new(&mut Scalar::deserialize(deserializer)?))
        }
    }

    /// Compact serialization format
    pub struct Compact;

    impl<E: Curve> serde_with::SerializeAs<Point<E>> for Compact {
        fn serialize_as<S>(source: &Point<E>, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            use serde::Serialize;
            models::PointCompact::from(source).serialize(serializer)
        }
    }

    impl<'de, E: Curve> serde_with::DeserializeAs<'de, Point<E>> for Compact {
        fn deserialize_as<D>(deserializer: D) -> Result<Point<E>, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            use serde::Deserialize;
            models::PointCompact::deserialize(deserializer)?
                .try_into()
                .map_err(<D::Error as serde::de::Error>::custom)
        }
    }

    impl<E: Curve> serde_with::SerializeAs<Scalar<E>> for Compact {
        fn serialize_as<S>(source: &Scalar<E>, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            use serde::Serialize;
            models::ScalarCompact::from(source).serialize(serializer)
        }
    }

    impl<'de, E: Curve> serde_with::DeserializeAs<'de, Scalar<E>> for Compact {
        fn deserialize_as<D>(deserializer: D) -> Result<Scalar<E>, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            use serde::Deserialize;
            models::ScalarCompact::deserialize(deserializer)?
                .try_into()
                .map_err(<D::Error as serde::de::Error>::custom)
        }
    }

    impl<E: Curve> serde_with::SerializeAs<SecretScalar<E>> for Compact {
        fn serialize_as<S>(source: &SecretScalar<E>, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            use serde::Serialize;
            models::ScalarCompact::from(source.as_ref()).serialize(serializer)
        }
    }

    impl<'de, E: Curve> serde_with::DeserializeAs<'de, SecretScalar<E>> for Compact {
        fn deserialize_as<D>(deserializer: D) -> Result<SecretScalar<E>, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            let mut scalar =
                <Compact as serde_with::DeserializeAs<'de, Scalar<E>>>::deserialize_as(
                    deserializer,
                )?;
            Ok(SecretScalar::new(&mut scalar))
        }
    }

    impl<T> serde_with::SerializeAs<crate::NonZero<T>> for Compact
    where
        Compact: serde_with::SerializeAs<T>,
    {
        fn serialize_as<S>(source: &crate::NonZero<T>, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            Compact::serialize_as(source.as_ref(), serializer)
        }
    }

    impl<'de, T> serde_with::DeserializeAs<'de, crate::NonZero<T>> for Compact
    where
        Compact: serde_with::DeserializeAs<'de, T>,
        crate::NonZero<T>: TryFrom<T>,
        <crate::NonZero<T> as TryFrom<T>>::Error: core::fmt::Display,
    {
        fn deserialize_as<D>(deserializer: D) -> Result<crate::NonZero<T>, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            let value = Compact::deserialize_as(deserializer)?;
            crate::NonZero::try_from(value).map_err(<D::Error as serde::de::Error>::custom)
        }
    }

    impl<'a, T> serde_with::SerializeAs<&'a T> for Compact
    where
        Compact: serde_with::SerializeAs<T>,
    {
        fn serialize_as<S>(source: &&'a T, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            Compact::serialize_as(*source, serializer)
        }
    }

    /// Serializes point/scalar compactly. Deserializes both compact
    /// and non-compact points/scalars.
    ///
    /// It can be used when some data used to be serialized in default serialization
    /// format, and at some point you decided to use a compact serialization format.
    /// `PreferCompact` serializes points/scalar in compact format, but at deserialization
    /// it accepts both compact and non-compact forms.
    ///
    /// `PreferCompact` does not work on `serde` backends which serialize structs as
    /// lists, such as `bincode`. Notably, (de)serialization of points/scalars in compact
    /// format will still work, but deserialization from non-compact form will produce
    /// an error.
    pub struct PreferCompact;

    impl<T> serde_with::SerializeAs<T> for PreferCompact
    where
        Compact: serde_with::SerializeAs<T>,
    {
        fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: serde::Serializer,
        {
            <Compact as serde_with::SerializeAs<T>>::serialize_as(source, serializer)
        }
    }

    impl<'de, T> serde_with::DeserializeAs<'de, T> for PreferCompact
    where
        T: serde::Deserialize<'de>,
        Compact: serde_with::DeserializeAs<'de, T>,
    {
        fn deserialize_as<D>(deserializer: D) -> Result<T, D::Error>
        where
            D: serde::Deserializer<'de>,
        {
            use serde_with::DeserializeAs;

            struct Visitor<T> {
                is_human_readable: bool,
                _out: core::marker::PhantomData<T>,
            }
            impl<'de, T> serde::de::Visitor<'de> for Visitor<T>
            where
                T: serde::Deserialize<'de>,
                Compact: serde_with::DeserializeAs<'de, T>,
            {
                type Value = T;
                fn expecting(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
                    f.write_str("preferably compact point/scalar")
                }

                fn visit_bytes<Err>(self, v: &[u8]) -> Result<Self::Value, Err>
                where
                    Err: serde::de::Error,
                {
                    Compact::deserialize_as(NewTypeDeserializer::new(OverrideHumanReadable {
                        deserializer: serde::de::value::BytesDeserializer::<Err>::new(v),
                        is_human_readable: self.is_human_readable,
                    }))
                }
                fn visit_str<Err>(self, v: &str) -> Result<Self::Value, Err>
                where
                    Err: serde::de::Error,
                {
                    Compact::deserialize_as(NewTypeDeserializer::new(OverrideHumanReadable {
                        deserializer: serde::de::value::StrDeserializer::<Err>::new(v),
                        is_human_readable: self.is_human_readable,
                    }))
                }

                fn visit_seq<A>(self, _seq: A) -> Result<Self::Value, A::Error>
                where
                    A: serde::de::SeqAccess<'de>,
                {
                    Err(<A::Error as serde::de::Error>::custom(
                        "cannot deserialize in `PreferCompact` mode \
                        from sequence: it's ambiguous",
                    ))
                }
                fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>
                where
                    A: serde::de::MapAccess<'de>,
                {
                    T::deserialize(OverrideHumanReadable {
                        deserializer: serde::de::value::MapAccessDeserializer::new(map),
                        is_human_readable: self.is_human_readable,
                    })
                }

                fn visit_newtype_struct<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
                where
                    D: serde::Deserializer<'de>,
                {
                    Compact::deserialize_as(NewTypeDeserializer::new(OverrideHumanReadable {
                        deserializer,
                        is_human_readable: self.is_human_readable,
                    }))
                }
            }

            let is_human_readable = deserializer.is_human_readable();
            deserializer.deserialize_any(Visitor {
                is_human_readable,
                _out: core::marker::PhantomData::<T>,
            })
        }
    }

    /// Wraps a [`serde::Deserializer`] and overrides `fn is_human_readable()`
    struct OverrideHumanReadable<D> {
        is_human_readable: bool,
        deserializer: D,
    }
    impl<'de, D> serde::Deserializer<'de> for OverrideHumanReadable<D>
    where
        D: serde::Deserializer<'de>,
    {
        type Error = <D as serde::Deserializer<'de>>::Error;

        fn is_human_readable(&self) -> bool {
            self.is_human_readable
        }

        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: serde::de::Visitor<'de>,
        {
            self.deserializer.deserialize_any(visitor)
        }

        serde::forward_to_deserialize_any! {
            bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
            bytes byte_buf option unit unit_struct newtype_struct seq tuple
            tuple_struct map struct enum identifier ignored_any
        }
    }

    /// See [`serde::de::value`]. New type deserializer is missing in the `serde` crate.
    struct NewTypeDeserializer<D> {
        deserializer: D,
    }
    impl<D> NewTypeDeserializer<D> {
        pub fn new(deserializer: D) -> Self {
            Self { deserializer }
        }
    }
    impl<'de, D> serde::Deserializer<'de> for NewTypeDeserializer<D>
    where
        D: serde::Deserializer<'de>,
    {
        type Error = D::Error;
        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
        where
            V: serde::de::Visitor<'de>,
        {
            visitor.visit_newtype_struct(self.deserializer)
        }
        fn is_human_readable(&self) -> bool {
            self.deserializer.is_human_readable()
        }
        serde::forward_to_deserialize_any! {
            bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
            bytes byte_buf option unit unit_struct newtype_struct seq tuple
            tuple_struct map struct enum identifier ignored_any
        }
    }

    mod models {
        use core::convert::TryFrom;

        use serde::{Deserialize, Serialize};
        use serde_with::serde_as;

        use crate::core::{CompressedEncoding, IntegerEncoding, UncompressedEncoding};
        use crate::{as_raw::AsRaw, Curve, Point, Scalar};

        use super::{
            error_msg::{InvalidPoint, InvalidScalar},
            CurveName,
        };

        #[serde_as]
        #[derive(Serialize, Deserialize)]
        #[serde(bound = "")]
        pub struct PointUncompressed<E: Curve> {
            curve: CurveName<E>,
            #[serde_as(as = "super::utils::Bytes")]
            point: E::UncompressedPointArray,
        }
        impl<E: Curve> From<&Point<E>> for PointUncompressed<E> {
            fn from(p: &Point<E>) -> Self {
                let bytes = p.as_raw().to_bytes_uncompressed();
                Self {
                    curve: CurveName::new(),
                    point: bytes,
                }
            }
        }
        impl<E: Curve> TryFrom<PointUncompressed<E>> for Point<E> {
            type Error = InvalidPoint;
            fn try_from(value: PointUncompressed<E>) -> Result<Self, Self::Error> {
                Point::from_bytes(value.point).or(Err(InvalidPoint))
            }
        }

        #[serde_as]
        #[derive(Serialize, Deserialize)]
        #[serde(bound = "")]
        pub struct PointCompact<E: Curve>(
            #[serde_as(as = "super::utils::Bytes")] E::CompressedPointArray,
        );
        impl<E: Curve> From<&Point<E>> for PointCompact<E> {
            fn from(p: &Point<E>) -> Self {
                let bytes = p.as_raw().to_bytes_compressed();
                Self(bytes)
            }
        }
        impl<E: Curve> TryFrom<PointCompact<E>> for Point<E> {
            type Error = InvalidPoint;
            fn try_from(value: PointCompact<E>) -> Result<Self, Self::Error> {
                Point::from_bytes(value.0).or(Err(InvalidPoint))
            }
        }

        #[serde_as]
        #[derive(Serialize, Deserialize)]
        #[serde(bound = "")]
        pub struct ScalarUncompressed<E: Curve> {
            curve: CurveName<E>,
            #[serde_as(as = "super::utils::Bytes")]
            scalar: E::ScalarArray,
        }
        impl<E: Curve> From<&Scalar<E>> for ScalarUncompressed<E> {
            fn from(s: &Scalar<E>) -> Self {
                let bytes = s.as_raw().to_be_bytes();
                Self {
                    curve: CurveName::new(),
                    scalar: bytes,
                }
            }
        }
        impl<E: Curve> TryFrom<ScalarUncompressed<E>> for Scalar<E> {
            type Error = InvalidScalar;
            fn try_from(value: ScalarUncompressed<E>) -> Result<Self, Self::Error> {
                Scalar::from_be_bytes(value.scalar).or(Err(InvalidScalar))
            }
        }

        #[serde_as]
        #[derive(Serialize, Deserialize)]
        #[serde(bound = "")]
        pub struct ScalarCompact<E: Curve>(#[serde_as(as = "super::utils::Bytes")] E::ScalarArray);
        impl<E: Curve> From<&Scalar<E>> for ScalarCompact<E> {
            fn from(s: &Scalar<E>) -> Self {
                let bytes = s.as_raw().to_be_bytes();
                Self(bytes)
            }
        }
        impl<E: Curve> TryFrom<ScalarCompact<E>> for Scalar<E> {
            type Error = InvalidScalar;
            fn try_from(value: ScalarCompact<E>) -> Result<Self, Self::Error> {
                Scalar::from_be_bytes(&value.0).or(Err(InvalidScalar))
            }
        }
    }

    mod utils {
        use core::fmt;

        use serde::de::{self, Visitor};
        use serde_with::{DeserializeAs, SerializeAs};

        use crate::core::ByteArray;

        pub struct Bytes;

        impl<T> SerializeAs<T> for Bytes
        where
            T: AsRef<[u8]>,
        {
            fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error>
            where
                S: serde::Serializer,
            {
                if serializer.is_human_readable() {
                    // We only support serialization of byte arrays up to 128 bytes. It can be generalized when
                    // Rust has better support of const generics
                    let mut buf = [0u8; 256];

                    if source.as_ref().len() * 2 > buf.len() {
                        return Err(<S::Error as serde::ser::Error>::custom(
                            super::error_msg::ByteArrayTooLarge {
                                len: source.as_ref().len(),
                                supported_len: buf.len() / 2,
                            },
                        ));
                    }
                    let buf = &mut buf[..2 * source.as_ref().len()];
                    hex::encode_to_slice(source, buf)
                        .map_err(<S::Error as serde::ser::Error>::custom)?;
                    let buf_str = core::str::from_utf8(buf).map_err(|e| {
                        <S::Error as serde::ser::Error>::custom(super::error_msg::MalformedHex(e))
                    })?;
                    serializer.serialize_str(buf_str)
                } else {
                    serializer.serialize_bytes(source.as_ref())
                }
            }
        }

        impl<'de, T> DeserializeAs<'de, T> for Bytes
        where
            T: ByteArray,
        {
            fn deserialize_as<D>(deserializer: D) -> Result<T, D::Error>
            where
                D: serde::Deserializer<'de>,
            {
                pub struct BytesVisitor<T>(T);
                impl<'de, T: AsMut<[u8]>> Visitor<'de> for BytesVisitor<T> {
                    type Value = T;
                    fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
                        write!(f, "bytes")
                    }
                    fn visit_str<E>(mut self, v: &str) -> Result<Self::Value, E>
                    where
                        E: serde::de::Error,
                    {
                        hex::decode_to_slice(v, self.0.as_mut()).map_err(E::custom)?;
                        Ok(self.0)
                    }
                    fn visit_bytes<E>(mut self, v: &[u8]) -> Result<Self::Value, E>
                    where
                        E: serde::de::Error,
                    {
                        let expected_len = self.0.as_mut().len();
                        if v.len() != expected_len {
                            return Err(E::invalid_length(
                                v.len(),
                                &super::error_msg::ExpectedLen(expected_len),
                            ));
                        }
                        self.0.as_mut().copy_from_slice(v);
                        Ok(self.0)
                    }
                    fn visit_seq<A>(mut self, mut seq: A) -> Result<Self::Value, A::Error>
                    where
                        A: serde::de::SeqAccess<'de>,
                    {
                        let expected_len = self.0.as_mut().len();
                        let bytes = self.0.as_mut().iter_mut().enumerate();

                        for (i, byte_i) in bytes {
                            let byte_parsed = seq.next_element()?.ok_or_else(|| {
                                <A::Error as de::Error>::invalid_length(
                                    i,
                                    &super::error_msg::ExpectedLen(expected_len),
                                )
                            })?;
                            *byte_i = byte_parsed;
                        }

                        let mut unparsed_bytes = 0;
                        while seq.next_element::<serde::de::IgnoredAny>()?.is_some() {
                            unparsed_bytes += 1
                        }

                        if unparsed_bytes > 0 {
                            Err(<A::Error as de::Error>::invalid_length(
                                expected_len + unparsed_bytes,
                                &super::error_msg::ExpectedLen(expected_len),
                            ))
                        } else {
                            Ok(self.0)
                        }
                    }
                }
                let visitor = BytesVisitor(T::zeroes());
                if deserializer.is_human_readable() {
                    deserializer.deserialize_str(visitor)
                } else {
                    deserializer.deserialize_bytes(visitor)
                }
            }
        }
    }

    pub(super) mod error_msg {
        use core::fmt;

        use serde::de::Expected;

        pub struct ExpectedCurve<'g> {
            pub expected: &'static str,
            pub got: &'g str,
        }

        impl fmt::Display for ExpectedCurve<'_> {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                write!(
                    f,
                    "expected {e} curve, got {g}",
                    e = self.expected,
                    g = self.got
                )
            }
        }

        pub struct ExpectedLen(pub usize);

        impl Expected for ExpectedLen {
            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                write!(f, "{} bytes", self.0)
            }
        }

        pub struct InvalidPoint;
        impl fmt::Display for InvalidPoint {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                write!(f, "invalid point")
            }
        }

        pub struct InvalidScalar;
        impl fmt::Display for InvalidScalar {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                write!(f, "invalid scalar")
            }
        }

        pub struct MalformedHex(pub core::str::Utf8Error);
        impl fmt::Display for MalformedHex {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                write!(f, "malformed hex: {}", self.0)
            }
        }

        pub struct ByteArrayTooLarge {
            pub len: usize,
            pub supported_len: usize,
        }
        impl fmt::Display for ByteArrayTooLarge {
            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                write!(f, "byte array is too large: its length is {} bytes, but only up to {} bytes can be serialized", self.len, self.supported_len)
            }
        }
    }
}