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//! Asymmetric crypt operations.

use nettle::{dsa, ecc, ecdsa, ed25519, rsa, Yarrow};

use packet::Key;
use crypto::mpis::{self, MPI};
use constants::{Curve, HashAlgorithm};

use Error;
use Result;

/// Creates a signature.
///
/// This is a low-level mechanism to produce an arbitrary OpenPGP
/// signature.  Using this trait allows Sequoia to perform all
/// operations involving signing to use a variety of secret key
/// storage mechanisms (e.g. smart cards).
pub trait Signer {
    /// Returns a reference to the public key.
    fn public(&self) -> &Key;

    /// Creates a signature over the `digest` produced by `hash_algo`.
    fn sign(&mut self, hash_algo: HashAlgorithm, digest: &[u8])
            -> Result<mpis::Signature>;
}

/// A cryptographic key pair.
///
/// A `KeyPair` is a combination of public and secret key.  If both
/// are available in memory, a `KeyPair` is a convenient
/// implementation of [`Signer`].
///
/// [`Signer`]: trait.Signer.html
pub struct KeyPair {
    public: Key,
    secret: mpis::SecretKey,
}

impl KeyPair {
    /// Creates a new key pair.
    pub fn new(public: Key, secret: mpis::SecretKey) -> Result<Self> {
        Ok(Self {
            public: public,
            secret: secret,
        })
    }
}

impl Signer for KeyPair {
    fn public(&self) -> &Key {
        &self.public
    }

    fn sign(&mut self, hash_algo: HashAlgorithm, digest: &[u8])
            -> Result<mpis::Signature>
    {
        use PublicKeyAlgorithm::*;
        use crypto::mpis::PublicKey;
        use memsec;

        let mut rng = Yarrow::default();

        #[allow(deprecated)]
        match (self.public.pk_algo(), self.public.mpis(), &self.secret)
        {
            (RSASign,
             &PublicKey::RSA { ref e, ref n },
             &mpis::SecretKey::RSA { ref p, ref q, ref d, .. }) |
            (RSAEncryptSign,
             &PublicKey::RSA { ref e, ref n },
             &mpis::SecretKey::RSA { ref p, ref q, ref d, .. }) => {
                let public = rsa::PublicKey::new(&n.value, &e.value)?;
                let secret = rsa::PrivateKey::new(&d.value, &p.value,
                                                  &q.value, Option::None)?;

                // The signature has the length of the modulus.
                let mut sig = vec![0u8; n.value.len()];

                // As described in [Section 5.2.2 and 5.2.3 of RFC 4880],
                // to verify the signature, we need to encode the
                // signature data in a PKCS1-v1.5 packet.
                //
                //   [Section 5.2.2 and 5.2.3 of RFC 4880]:
                //   https://tools.ietf.org/html/rfc4880#section-5.2.2
                rsa::sign_digest_pkcs1(&public, &secret, digest,
                                       hash_algo.oid()?,
                                       &mut rng, &mut sig)?;

                Ok(mpis::Signature::RSA {
                    s: MPI::new(&sig),
                })
            },

            (DSA,
             &PublicKey::DSA { ref p, ref q, ref g, .. },
             &mpis::SecretKey::DSA { ref x }) => {
                let params = dsa::Params::new(&p.value, &q.value, &g.value);
                let secret = dsa::PrivateKey::new(&x.value);

                let sig = dsa::sign(&params, &secret, digest, &mut rng)?;

                Ok(mpis::Signature::DSA {
                    r: MPI::new(&sig.r()),
                    s: MPI::new(&sig.s()),
                })
            },

            (EdDSA,
             &PublicKey::EdDSA { ref curve, ref q },
             &mpis::SecretKey::EdDSA { ref scalar }) => match curve {
                Curve::Ed25519 => {
                    let public = q.decode_point(&Curve::Ed25519)?.0;

                    let mut sig = vec![0; ed25519::ED25519_SIGNATURE_SIZE];

                    // Nettle expects the private key to be exactly
                    // ED25519_KEY_SIZE bytes long but OpenPGP allows leading
                    // zeros to be stripped.
                    // Padding has to be unconditionaly, otherwise we have a
                    // secret-dependant branch.
                    let missing = ed25519::ED25519_KEY_SIZE
                        .saturating_sub(scalar.value.len());
                    let mut sec = [0u8; ed25519::ED25519_KEY_SIZE];
                    sec[missing..].copy_from_slice(&scalar.value[..]);

                    let res = ed25519::sign(public, &sec[..], digest, &mut sig);
                    unsafe {
                        memsec::memzero(sec.as_mut_ptr(),
                                        ed25519::ED25519_KEY_SIZE);
                    }
                    res?;

                    Ok(mpis::Signature::EdDSA {
                        r: MPI::new(&sig[..32]),
                        s: MPI::new(&sig[32..]),
                    })
                },
                _ => Err(
                    Error::UnsupportedEllipticCurve(curve.clone()).into()),
            },

            (ECDSA,
             &PublicKey::ECDSA { ref curve, .. },
             &mpis::SecretKey::ECDSA { ref scalar }) => {
                let secret = match curve {
                    Curve::NistP256 =>
                        ecc::Scalar::new::<ecc::Secp256r1>(
                            &scalar.value)?,
                    Curve::NistP384 =>
                        ecc::Scalar::new::<ecc::Secp384r1>(
                            &scalar.value)?,
                    Curve::NistP521 =>
                        ecc::Scalar::new::<ecc::Secp521r1>(
                            &scalar.value)?,
                    _ =>
                        return Err(
                            Error::UnsupportedEllipticCurve(curve.clone())
                                .into()),
                };

                let sig = ecdsa::sign(&secret, digest, &mut rng);

                Ok(mpis::Signature::ECDSA {
                    r: MPI::new(&sig.r()),
                    s: MPI::new(&sig.s()),
                })
            },

            (pk_algo, _, _) => Err(Error::InvalidArgument(format!(
                "unsupported combination of algorithm {:?}, key {:?}, \
                 and secret key {:?}",
                pk_algo, self.public, self.secret)).into()),
        }
    }
}