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//! Rivest–Shamir–Adleman (RSA) public keys.

use crate::{
    checked::CheckedSum, decode::Decode, encode::Encode, reader::Reader, writer::Writer, MPInt,
    Result,
};

#[cfg(feature = "rsa")]
use {
    crate::{private::RsaKeypair, Error},
    rsa::PublicKeyParts,
};

/// RSA public key.
///
/// Described in [RFC4253 § 6.6](https://datatracker.ietf.org/doc/html/rfc4253#section-6.6):
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
pub struct RsaPublicKey {
    /// RSA public exponent.
    pub e: MPInt,

    /// RSA modulus.
    pub n: MPInt,
}

impl RsaPublicKey {
    /// Minimum allowed RSA key size.
    #[cfg(feature = "rsa")]
    pub(crate) const MIN_KEY_SIZE: usize = RsaKeypair::MIN_KEY_SIZE;
}

impl Decode for RsaPublicKey {
    fn decode(reader: &mut impl Reader) -> Result<Self> {
        let e = MPInt::decode(reader)?;
        let n = MPInt::decode(reader)?;
        Ok(Self { e, n })
    }
}

impl Encode for RsaPublicKey {
    fn encoded_len(&self) -> Result<usize> {
        [self.e.encoded_len()?, self.n.encoded_len()?].checked_sum()
    }

    fn encode(&self, writer: &mut impl Writer) -> Result<()> {
        self.e.encode(writer)?;
        self.n.encode(writer)
    }
}

#[cfg(feature = "rsa")]
#[cfg_attr(docsrs, doc(cfg(feature = "rsa")))]
impl TryFrom<RsaPublicKey> for rsa::RsaPublicKey {
    type Error = Error;

    fn try_from(key: RsaPublicKey) -> Result<rsa::RsaPublicKey> {
        rsa::RsaPublicKey::try_from(&key)
    }
}

#[cfg(feature = "rsa")]
#[cfg_attr(docsrs, doc(cfg(feature = "rsa")))]
impl TryFrom<&RsaPublicKey> for rsa::RsaPublicKey {
    type Error = Error;

    fn try_from(key: &RsaPublicKey) -> Result<rsa::RsaPublicKey> {
        let ret = rsa::RsaPublicKey::new(
            rsa::BigUint::try_from(&key.n)?,
            rsa::BigUint::try_from(&key.e)?,
        )
        .map_err(|_| Error::Crypto)?;

        if ret.size().saturating_mul(8) >= RsaPublicKey::MIN_KEY_SIZE {
            Ok(ret)
        } else {
            Err(Error::Crypto)
        }
    }
}

#[cfg(feature = "rsa")]
#[cfg_attr(docsrs, doc(cfg(feature = "rsa")))]
impl TryFrom<rsa::RsaPublicKey> for RsaPublicKey {
    type Error = Error;

    fn try_from(key: rsa::RsaPublicKey) -> Result<RsaPublicKey> {
        RsaPublicKey::try_from(&key)
    }
}

#[cfg(feature = "rsa")]
#[cfg_attr(docsrs, doc(cfg(feature = "rsa")))]
impl TryFrom<&rsa::RsaPublicKey> for RsaPublicKey {
    type Error = Error;

    fn try_from(key: &rsa::RsaPublicKey) -> Result<RsaPublicKey> {
        Ok(RsaPublicKey {
            e: key.e().try_into()?,
            n: key.n().try_into()?,
        })
    }
}