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    //! Digital Signatures
    //!
    //! DSA ensures a message originated from a known sender, and was not modified.
    //! DSA uses asymetrical keys and an algorithm to output a signature of the message
    //! using the private key that can be validated with the public key but not be generated
    //! without the private key.

    use ffi;
    use foreign_types::{ForeignType, ForeignTypeRef};
    use libc::c_int;
    use std::fmt;
    use std::mem;
    use std::ptr;

    use bn::{BigNum, BigNumRef};
    use error::ErrorStack;
    use pkey::{HasParams, HasPrivate, HasPublic, Private, Public};
    use util::ForeignTypeRefExt;
    use {cvt, cvt_p};

    generic_foreign_type_and_impl_send_sync! {
        type CType = ffi::DSA;
        fn drop = ffi::DSA_free;

        /// Object representing DSA keys.
        ///
        /// A DSA object contains the parameters p, q, and g.  There is a private
        /// and public key.  The values p, g, and q are:
        ///
        /// * `p`: DSA prime parameter
        /// * `q`: DSA sub-prime parameter
        /// * `g`: DSA base parameter
        ///
        /// These values are used to calculate a pair of asymetrical keys used for
        /// signing.
        ///
        /// OpenSSL documentation at [`DSA_new`]
        ///
        /// [`DSA_new`]: https://www.openssl.org/docs/man1.1.0/crypto/DSA_new.html
        ///
        /// # Examples
        ///
        /// ```
        /// use openssl::dsa::Dsa;
        /// use openssl::error::ErrorStack;
        /// use openssl::pkey::Private;
        ///
        /// fn create_dsa() -> Result<Dsa<Private>, ErrorStack> {
        ///     let sign = Dsa::generate(2048)?;
        ///     Ok(sign)
        /// }
        /// # fn main() {
        /// #    create_dsa();
        /// # }
        /// ```
        pub struct Dsa<T>;
        /// Reference to [`Dsa`].
        ///
        /// [`Dsa`]: struct.Dsa.html
        pub struct DsaRef<T>;
    }

    impl<T> Clone for Dsa<T> {
        fn clone(&self) -> Dsa<T> {
            (**self).to_owned()
        }
    }

    impl<T> ToOwned for DsaRef<T> {
        type Owned = Dsa<T>;

        fn to_owned(&self) -> Dsa<T> {
            unsafe {
                ffi::DSA_up_ref(self.as_ptr());
                Dsa::from_ptr(self.as_ptr())
            }
        }
    }

    impl<T> DsaRef<T>
    where
        T: HasPublic,
    {
        to_pem! {
            /// Serialies the public key into a PEM-encoded SubjectPublicKeyInfo structure.
            ///
            /// The output will have a header of `-----BEGIN PUBLIC KEY-----`.
            ///
            /// This corresponds to [`PEM_write_bio_DSA_PUBKEY`].
            ///
            /// [`PEM_write_bio_DSA_PUBKEY`]: https://www.openssl.org/docs/man1.1.0/crypto/PEM_write_bio_DSA_PUBKEY.html
            public_key_to_pem,
            ffi::PEM_write_bio_DSA_PUBKEY
        }

        to_der! {
            /// Serializes the public key into a DER-encoded SubjectPublicKeyInfo structure.
            ///
            /// This corresponds to [`i2d_DSA_PUBKEY`].
            ///
            /// [`i2d_DSA_PUBKEY`]: https://www.openssl.org/docs/man1.1.0/crypto/i2d_DSA_PUBKEY.html
            public_key_to_der,
            ffi::i2d_DSA_PUBKEY
        }

        /// Returns a reference to the public key component of `self`.
        pub fn pub_key(&self) -> &BigNumRef {
            unsafe {
                let mut pub_key = ptr::null();
                DSA_get0_key(self.as_ptr(), &mut pub_key, ptr::null_mut());
                BigNumRef::from_const_ptr(pub_key)
            }
        }
    }

    impl<T> DsaRef<T>
    where
        T: HasPrivate,
    {
        private_key_to_pem! {
            /// Serializes the private key to a PEM-encoded DSAPrivateKey structure.
            ///
            /// The output will have a header of `-----BEGIN DSA PRIVATE KEY-----`.
            ///
            /// This corresponds to [`PEM_write_bio_DSAPrivateKey`].
            ///
            /// [`PEM_write_bio_DSAPrivateKey`]: https://www.openssl.org/docs/man1.1.0/crypto/PEM_write_bio_DSAPrivateKey.html
            private_key_to_pem,
            /// Serializes the private key to a PEM-encoded encrypted DSAPrivateKey structure.
            ///
            /// The output will have a header of `-----BEGIN DSA PRIVATE KEY-----`.
            ///
            /// This corresponds to [`PEM_write_bio_DSAPrivateKey`].
            ///
            /// [`PEM_write_bio_DSAPrivateKey`]: https://www.openssl.org/docs/man1.1.0/crypto/PEM_write_bio_DSAPrivateKey.html
            private_key_to_pem_passphrase,
            ffi::PEM_write_bio_DSAPrivateKey
        }

        /// Returns a reference to the private key component of `self`.
        pub fn priv_key(&self) -> &BigNumRef {
            unsafe {
                let mut priv_key = ptr::null();
                DSA_get0_key(self.as_ptr(), ptr::null_mut(), &mut priv_key);
                BigNumRef::from_const_ptr(priv_key)
            }
        }
    }

    impl<T> DsaRef<T>
    where
        T: HasParams,
    {
        /// Returns the maximum size of the signature output by `self` in bytes.
        ///
        /// OpenSSL documentation at [`DSA_size`]
        ///
        /// [`DSA_size`]: https://www.openssl.org/docs/man1.1.0/crypto/DSA_size.html
        pub fn size(&self) -> u32 {
            unsafe { ffi::DSA_size(self.as_ptr()) as u32 }
        }

        /// Returns the DSA prime parameter of `self`.
        pub fn p(&self) -> &BigNumRef {
            unsafe {
                let mut p = ptr::null();
                DSA_get0_pqg(self.as_ptr(), &mut p, ptr::null_mut(), ptr::null_mut());
                BigNumRef::from_const_ptr(p)
            }
        }

        /// Returns the DSA sub-prime parameter of `self`.
        pub fn q(&self) -> &BigNumRef {
            unsafe {
                let mut q = ptr::null();
                DSA_get0_pqg(self.as_ptr(), ptr::null_mut(), &mut q, ptr::null_mut());
                BigNumRef::from_const_ptr(q)
            }
        }

        /// Returns the DSA base parameter of `self`.
        pub fn g(&self) -> &BigNumRef {
            unsafe {
                let mut g = ptr::null();
                DSA_get0_pqg(self.as_ptr(), ptr::null_mut(), ptr::null_mut(), &mut g);
                BigNumRef::from_const_ptr(g)
            }
        }
    }

    impl Dsa<Private> {
        /// Generate a DSA key pair.
        ///
        /// Calls [`DSA_generate_parameters_ex`] to populate the `p`, `g`, and `q` values.
        /// These values are used to generate the key pair with [`DSA_generate_key`].
        ///
        /// The `bits` parameter corresponds to the length of the prime `p`.
        ///
        /// [`DSA_generate_parameters_ex`]: https://www.openssl.org/docs/man1.1.0/crypto/DSA_generate_parameters_ex.html
        /// [`DSA_generate_key`]: https://www.openssl.org/docs/man1.1.0/crypto/DSA_generate_key.html
        pub fn generate(bits: u32) -> Result<Dsa<Private>, ErrorStack> {
            ffi::init();
            unsafe {
                let dsa = Dsa::from_ptr(cvt_p(ffi::DSA_new())?);
                cvt(ffi::DSA_generate_parameters_ex(
                    dsa.0,
                    bits as c_int,
                    ptr::null(),
                    0,
                    ptr::null_mut(),
                    ptr::null_mut(),
                    ptr::null_mut(),
                ))?;
                cvt(ffi::DSA_generate_key(dsa.0))?;
                Ok(dsa)
            }
        }

        /// Create a DSA key pair with the given parameters
        ///
        /// `p`, `q` and `g` are the common parameters.
        /// `priv_key` is the private component of the key pair.
        /// `pub_key` is the public component of the key. Can be computed via `g^(priv_key) mod p`
        pub fn from_private_components(
            p: BigNum,
            q: BigNum,
            g: BigNum,
            priv_key: BigNum,
            pub_key: BigNum,
        ) -> Result<Dsa<Private>, ErrorStack> {
            ffi::init();
            unsafe {
                let dsa = Dsa::from_ptr(cvt_p(ffi::DSA_new())?);
                cvt(DSA_set0_pqg(dsa.0, p.as_ptr(), q.as_ptr(), g.as_ptr()))?;
                mem::forget((p, q, g));
                cvt(DSA_set0_key(dsa.0, pub_key.as_ptr(), priv_key.as_ptr()))?;
                mem::forget((pub_key, priv_key));
                Ok(dsa)
            }
        }
    }

    impl Dsa<Public> {
        from_pem! {
            /// Decodes a PEM-encoded SubjectPublicKeyInfo structure containing a DSA key.
            ///
            /// The input should have a header of `-----BEGIN PUBLIC KEY-----`.
            ///
            /// This corresponds to [`PEM_read_bio_DSA_PUBKEY`].
            ///
            /// [`PEM_read_bio_DSA_PUBKEY`]: https://www.openssl.org/docs/man1.0.2/crypto/PEM_read_bio_DSA_PUBKEY.html
            public_key_from_pem,
            Dsa<Public>,
            ffi::PEM_read_bio_DSA_PUBKEY
        }

        from_der! {
            /// Decodes a DER-encoded SubjectPublicKeyInfo structure containing a DSA key.
            ///
            /// This corresponds to [`d2i_DSA_PUBKEY`].
            ///
            /// [`d2i_DSA_PUBKEY`]: https://www.openssl.org/docs/man1.0.2/crypto/d2i_DSA_PUBKEY.html
            public_key_from_der,
            Dsa<Public>,
            ffi::d2i_DSA_PUBKEY
        }

        /// Create a new DSA key with only public components.
        ///
        /// `p`, `q` and `g` are the common parameters.
        /// `pub_key` is the public component of the key.
        pub fn from_public_components(
            p: BigNum,
            q: BigNum,
            g: BigNum,
            pub_key: BigNum,
        ) -> Result<Dsa<Public>, ErrorStack> {
            ffi::init();
            unsafe {
                let dsa = Dsa::from_ptr(cvt_p(ffi::DSA_new())?);
                cvt(DSA_set0_pqg(dsa.0, p.as_ptr(), q.as_ptr(), g.as_ptr()))?;
                mem::forget((p, q, g));
                cvt(DSA_set0_key(dsa.0, pub_key.as_ptr(), ptr::null_mut()))?;
                mem::forget(pub_key);
                Ok(dsa)
            }
        }
    }

    impl<T> fmt::Debug for Dsa<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "DSA")
        }
    }

    cfg_if! {
        if #[cfg(any(ossl110, libressl273))] {
            use ffi::{DSA_get0_key, DSA_get0_pqg, DSA_set0_key, DSA_set0_pqg};
        } else {
            #[allow(bad_style)]
            unsafe fn DSA_get0_pqg(
                d: *mut ffi::DSA,
                p: *mut *const ffi::BIGNUM,
                q: *mut *const ffi::BIGNUM,
                g: *mut *const ffi::BIGNUM)
            {
                if !p.is_null() {
                    *p = (*d).p;
                }
                if !q.is_null() {
                    *q = (*d).q;
                }
                if !g.is_null() {
                    *g = (*d).g;
                }
            }

            #[allow(bad_style)]
            unsafe fn DSA_get0_key(
                d: *mut ffi::DSA,
                pub_key: *mut *const ffi::BIGNUM,
                priv_key: *mut *const ffi::BIGNUM)
            {
                if !pub_key.is_null() {
                    *pub_key = (*d).pub_key;
                }
                if !priv_key.is_null() {
                    *priv_key = (*d).priv_key;
                }
            }

            #[allow(bad_style)]
            unsafe fn DSA_set0_key(
                d: *mut ffi::DSA,
                pub_key: *mut ffi::BIGNUM,
                priv_key: *mut ffi::BIGNUM) -> c_int
            {
                (*d).pub_key = pub_key;
                (*d).priv_key = priv_key;
                1
            }

            #[allow(bad_style)]
            unsafe fn DSA_set0_pqg(
                d: *mut ffi::DSA,
                p: *mut ffi::BIGNUM,
                q: *mut ffi::BIGNUM,
                g: *mut ffi::BIGNUM) -> c_int
            {
                (*d).p = p;
                (*d).q = q;
                (*d).g = g;
                1
            }
        }
    }

    #[cfg(test)]
    mod test {
        use super::*;
        use bn::BigNumContext;
        use hash::MessageDigest;
        use pkey::PKey;
        use sign::{Signer, Verifier};

        #[test]
        pub fn test_generate() {
            Dsa::generate(1024).unwrap();
        }

        #[test]
        fn test_pubkey_generation() {
            let dsa = Dsa::generate(1024).unwrap();
            let p = dsa.p();
            let g = dsa.g();
            let priv_key = dsa.priv_key();
            let pub_key = dsa.pub_key();
            let mut ctx = BigNumContext::new().unwrap();
            let mut calc = BigNum::new().unwrap();
            calc.mod_exp(g, priv_key, p, &mut ctx).unwrap();
            assert_eq!(&calc, pub_key)
        }

        #[test]
        fn test_priv_key_from_parts() {
            let p = BigNum::from_u32(283).unwrap();
            let q = BigNum::from_u32(47).unwrap();
            let g = BigNum::from_u32(60).unwrap();
            let priv_key = BigNum::from_u32(15).unwrap();
            let pub_key = BigNum::from_u32(207).unwrap();

            let dsa = Dsa::from_private_components(p, q, g, priv_key, pub_key).unwrap();
            assert_eq!(dsa.pub_key(), &BigNum::from_u32(207).unwrap());
            assert_eq!(dsa.priv_key(), &BigNum::from_u32(15).unwrap());
            assert_eq!(dsa.p(), &BigNum::from_u32(283).unwrap());
            assert_eq!(dsa.q(), &BigNum::from_u32(47).unwrap());
            assert_eq!(dsa.g(), &BigNum::from_u32(60).unwrap());
        }

        #[test]
        fn test_pub_key_from_parts() {
            let p = BigNum::from_u32(283).unwrap();
            let q = BigNum::from_u32(47).unwrap();
            let g = BigNum::from_u32(60).unwrap();
            let pub_key = BigNum::from_u32(207).unwrap();

            let dsa = Dsa::from_public_components(p, q, g, pub_key).unwrap();
            assert_eq!(dsa.pub_key(), &BigNum::from_u32(207).unwrap());
            assert_eq!(dsa.p(), &BigNum::from_u32(283).unwrap());
            assert_eq!(dsa.q(), &BigNum::from_u32(47).unwrap());
            assert_eq!(dsa.g(), &BigNum::from_u32(60).unwrap());
        }

        #[test]
        fn test_signature() {
            const TEST_DATA: &[u8] = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
            let dsa_ref = Dsa::generate(1024).unwrap();

            let p = dsa_ref.p();
            let q = dsa_ref.q();
            let g = dsa_ref.g();

            let pub_key = dsa_ref.pub_key();
            let priv_key = dsa_ref.priv_key();

            let priv_key = Dsa::from_private_components(
                BigNumRef::to_owned(p).unwrap(),
                BigNumRef::to_owned(q).unwrap(),
                BigNumRef::to_owned(g).unwrap(),
                BigNumRef::to_owned(priv_key).unwrap(),
                BigNumRef::to_owned(pub_key).unwrap(),
            )
            .unwrap();
            let priv_key = PKey::from_dsa(priv_key).unwrap();

            let pub_key = Dsa::from_public_components(
                BigNumRef::to_owned(p).unwrap(),
                BigNumRef::to_owned(q).unwrap(),
                BigNumRef::to_owned(g).unwrap(),
                BigNumRef::to_owned(pub_key).unwrap(),
            )
            .unwrap();
            let pub_key = PKey::from_dsa(pub_key).unwrap();

            let mut signer = Signer::new(MessageDigest::sha256(), &priv_key).unwrap();
            signer.update(TEST_DATA).unwrap();

            let signature = signer.sign_to_vec().unwrap();
            let mut verifier = Verifier::new(MessageDigest::sha256(), &pub_key).unwrap();
            verifier.update(TEST_DATA).unwrap();
            assert!(verifier.verify(&signature[..]).unwrap());
        }

        #[test]
        #[allow(clippy::redundant_clone)]
        fn clone() {
            let key = Dsa::generate(2048).unwrap();
            drop(key.clone());
        }
    }