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    //! Low level Elliptic Curve Digital Signature Algorithm (ECDSA) functions.

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

    use bn::{BigNum, BigNumRef};
    use ec::EcKeyRef;
    use error::ErrorStack;
    use pkey::{HasPrivate, HasPublic};
    use util::ForeignTypeRefExt;
    use {cvt_n, cvt_p};

    foreign_type_and_impl_send_sync! {
        type CType = ffi::ECDSA_SIG;
        fn drop = ffi::ECDSA_SIG_free;

        /// A low level interface to ECDSA
        ///
        /// OpenSSL documentation at [`ECDSA_sign`]
        ///
        /// [`ECDSA_sign`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_sign.html
        pub struct EcdsaSig;
        /// Reference to [`EcdsaSig`]
        ///
        /// [`EcdsaSig`]: struct.EcdsaSig.html
        pub struct EcdsaSigRef;
    }

    impl EcdsaSig {
        /// Computes a digital signature of the hash value `data` using the private EC key eckey.
        ///
        /// OpenSSL documentation at [`ECDSA_do_sign`]
        ///
        /// [`ECDSA_do_sign`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_do_sign.html
        pub fn sign<T>(data: &[u8], eckey: &EcKeyRef<T>) -> Result<EcdsaSig, ErrorStack>
        where
            T: HasPrivate,
        {
            unsafe {
                assert!(data.len() <= c_int::max_value() as usize);
                let sig = cvt_p(ffi::ECDSA_do_sign(
                    data.as_ptr(),
                    data.len() as c_int,
                    eckey.as_ptr(),
                ))?;
                Ok(EcdsaSig::from_ptr(sig))
            }
        }

        /// Returns a new `EcdsaSig` by setting the `r` and `s` values associated with a
        /// ECDSA signature.
        ///
        /// OpenSSL documentation at [`ECDSA_SIG_set0`]
        ///
        /// [`ECDSA_SIG_set0`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_SIG_set0.html
        pub fn from_private_components(r: BigNum, s: BigNum) -> Result<EcdsaSig, ErrorStack> {
            unsafe {
                let sig = cvt_p(ffi::ECDSA_SIG_new())?;
                ECDSA_SIG_set0(sig, r.as_ptr(), s.as_ptr());
                mem::forget((r, s));
                Ok(EcdsaSig::from_ptr(sig))
            }
        }

        from_der! {
            /// Decodes a DER-encoded ECDSA signature.
            ///
            /// This corresponds to [`d2i_ECDSA_SIG`].
            ///
            /// [`d2i_ECDSA_SIG`]: https://www.openssl.org/docs/man1.1.0/crypto/d2i_ECDSA_SIG.html
            from_der,
            EcdsaSig,
            ffi::d2i_ECDSA_SIG
        }
    }

    impl EcdsaSigRef {
        to_der! {
            /// Serializes the ECDSA signature into a DER-encoded ECDSASignature structure.
            ///
            /// This corresponds to [`i2d_ECDSA_SIG`].
            ///
            /// [`i2d_ECDSA_SIG`]: https://www.openssl.org/docs/man1.1.0/crypto/i2d_ECDSA_SIG.html
            to_der,
            ffi::i2d_ECDSA_SIG
        }

        /// Verifies if the signature is a valid ECDSA signature using the given public key.
        ///
        /// OpenSSL documentation at [`ECDSA_do_verify`]
        ///
        /// [`ECDSA_do_verify`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_do_verify.html
        pub fn verify<T>(&self, data: &[u8], eckey: &EcKeyRef<T>) -> Result<bool, ErrorStack>
        where
            T: HasPublic,
        {
            unsafe {
                assert!(data.len() <= c_int::max_value() as usize);
                cvt_n(ffi::ECDSA_do_verify(
                    data.as_ptr(),
                    data.len() as c_int,
                    self.as_ptr(),
                    eckey.as_ptr(),
                ))
                .map(|x| x == 1)
            }
        }

        /// Returns internal component: `r` of an `EcdsaSig`. (See X9.62 or FIPS 186-2)
        ///
        /// OpenSSL documentation at [`ECDSA_SIG_get0`]
        ///
        /// [`ECDSA_SIG_get0`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_SIG_get0.html
        pub fn r(&self) -> &BigNumRef {
            unsafe {
                let mut r = ptr::null();
                ECDSA_SIG_get0(self.as_ptr(), &mut r, ptr::null_mut());
                BigNumRef::from_const_ptr(r)
            }
        }

        /// Returns internal components: `s` of an `EcdsaSig`. (See X9.62 or FIPS 186-2)
        ///
        /// OpenSSL documentation at [`ECDSA_SIG_get0`]
        ///
        /// [`ECDSA_SIG_get0`]: https://www.openssl.org/docs/man1.1.0/crypto/ECDSA_SIG_get0.html
        pub fn s(&self) -> &BigNumRef {
            unsafe {
                let mut s = ptr::null();
                ECDSA_SIG_get0(self.as_ptr(), ptr::null_mut(), &mut s);
                BigNumRef::from_const_ptr(s)
            }
        }
    }

    cfg_if! {
        if #[cfg(any(ossl110, libressl273))] {
            use ffi::{ECDSA_SIG_set0, ECDSA_SIG_get0};
        } else {
            #[allow(bad_style)]
            unsafe fn ECDSA_SIG_set0(
                sig: *mut ffi::ECDSA_SIG,
                r: *mut ffi::BIGNUM,
                s: *mut ffi::BIGNUM,
            ) -> c_int {
                if r.is_null() || s.is_null() {
                    return 0;
                }
                ffi::BN_clear_free((*sig).r);
                ffi::BN_clear_free((*sig).s);
                (*sig).r = r;
                (*sig).s = s;
                1
            }

            #[allow(bad_style)]
            unsafe fn ECDSA_SIG_get0(
                sig: *const ffi::ECDSA_SIG,
                pr: *mut *const ffi::BIGNUM,
                ps: *mut *const ffi::BIGNUM)
            {
                if !pr.is_null() {
                    (*pr) = (*sig).r;
                }
                if !ps.is_null() {
                    (*ps) = (*sig).s;
                }
            }
        }
    }

    #[cfg(test)]
    mod test {
        use super::*;
        use ec::EcGroup;
        use ec::EcKey;
        use nid::Nid;
        use pkey::{Private, Public};

        fn get_public_key(group: &EcGroup, x: &EcKey<Private>) -> Result<EcKey<Public>, ErrorStack> {
            let public_key_point = x.public_key();
            Ok(EcKey::from_public_key(group, public_key_point)?)
        }

        #[test]
        #[cfg_attr(osslconf = "OPENSSL_NO_EC2M", ignore)]
        fn sign_and_verify() {
            let group = EcGroup::from_curve_name(Nid::X9_62_PRIME192V1).unwrap();
            let private_key = EcKey::generate(&group).unwrap();
            let public_key = get_public_key(&group, &private_key).unwrap();

            let private_key2 = EcKey::generate(&group).unwrap();
            let public_key2 = get_public_key(&group, &private_key2).unwrap();

            let data = String::from("hello");
            let res = EcdsaSig::sign(data.as_bytes(), &private_key).unwrap();

            // Signature can be verified using the correct data & correct public key
            let verification = res.verify(data.as_bytes(), &public_key).unwrap();
            assert!(verification);

            // Signature will not be verified using the incorrect data but the correct public key
            let verification2 = res
                .verify(String::from("hello2").as_bytes(), &public_key)
                .unwrap();
            assert!(!verification2);

            // Signature will not be verified using the correct data but the incorrect public key
            let verification3 = res.verify(data.as_bytes(), &public_key2).unwrap();
            assert!(!verification3);
        }

        #[test]
        #[cfg_attr(osslconf = "OPENSSL_NO_EC2M", ignore)]
        fn check_private_components() {
            let group = EcGroup::from_curve_name(Nid::X9_62_PRIME192V1).unwrap();
            let private_key = EcKey::generate(&group).unwrap();
            let public_key = get_public_key(&group, &private_key).unwrap();
            let data = String::from("hello");
            let res = EcdsaSig::sign(data.as_bytes(), &private_key).unwrap();

            let verification = res.verify(data.as_bytes(), &public_key).unwrap();
            assert!(verification);

            let r = res.r().to_owned().unwrap();
            let s = res.s().to_owned().unwrap();

            let res2 = EcdsaSig::from_private_components(r, s).unwrap();
            let verification2 = res2.verify(data.as_bytes(), &public_key).unwrap();
            assert!(verification2);
        }

        #[test]
        #[cfg_attr(osslconf = "OPENSSL_NO_EC2M", ignore)]
        fn serialize_deserialize() {
            let group = EcGroup::from_curve_name(Nid::SECP256K1).unwrap();
            let private_key = EcKey::generate(&group).unwrap();
            let public_key = get_public_key(&group, &private_key).unwrap();

            let data = String::from("hello");
            let res = EcdsaSig::sign(data.as_bytes(), &private_key).unwrap();

            let der = res.to_der().unwrap();
            let sig = EcdsaSig::from_der(&der).unwrap();

            let verification = sig.verify(data.as_bytes(), &public_key).unwrap();
            assert!(verification);
        }
    }