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    // Copyright 2017 Brian Smith.
    //
    // Permission to use, copy, modify, and/or distribute this software for any
    // purpose with or without fee is hereby granted, provided that the above
    // copyright notice and this permission notice appear in all copies.
    //
    // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
    // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
    // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
    // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
    // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

    //! PKCS#8 is specified in [RFC 5958].
    //!
    //! [RFC 5958]: https://tools.ietf.org/html/rfc5958.

    use core;
    use {der, ec, error};
    use untrusted;

    pub enum Version {
        V1Only,
        V1OrV2,
        V2Only,
    }

    /// A template for constructing PKCS#8 documents.
    ///
    /// Note that this only works for ECC.
    pub struct Template {
        pub bytes: &'static [u8],

        // The range within `bytes` that holds the value (not including the tag and
        // length) for use in the PKCS#8 document's privateKeyAlgorithm field.
        pub alg_id_range: core::ops::Range<usize>,

        // `bytes[alg_id_range][curve_id_index..]` contains the OID identifying the,
        // curve, including the tag and length.
        pub curve_id_index: usize,

        // `bytes` will be split into two parts at `private_key_index`, where the
        // first part is written before the private key and the second part is
        // written after the private key. The public key is written after the second
        // part.
        pub private_key_index: usize,
    }

    impl Template {
        #[inline]
        fn alg_id_value(&self) -> &[u8] {
            &self.bytes[self.alg_id_range.start..self.alg_id_range.end]
        }

        #[inline]
        pub fn curve_oid(&self) -> &[u8] {
            &self.alg_id_value()[self.curve_id_index..]
        }
    }

    /// Parses an unencrypted PKCS#8 private key, verifies that it is the right type
    /// of key, and returns the key value.
    ///
    /// PKCS#8 is specified in [RFC 5958].
    ///
    /// [RFC 5958]: https://tools.ietf.org/html/rfc5958.
    pub fn unwrap_key<'a>(template: &Template, version: Version,
                          input: untrusted::Input<'a>)
            -> Result<(untrusted::Input<'a>, Option<untrusted::Input<'a>>),
                       error::Unspecified> {
        unwrap_key_(template.alg_id_value(), version, input)
    }

    /// Parses an unencrypted PKCS#8 private key, verifies that it is the right type
    /// of key, and returns the key value.
    ///
    /// `alg_id` must be the encoded value (not including the outermost `SEQUENCE`
    /// tag and length) of the `AlgorithmIdentifier` that identifies the key type.
    /// The result will be an encoded `RSAPrivateKey` or `ECPrivateKey` or similar.
    ///
    /// PKCS#8 is specified in [RFC 5958].
    ///
    /// [RFC 5958]: https://tools.ietf.org/html/rfc5958.
    pub fn unwrap_key_<'a>(alg_id: &[u8], version: Version,
                           input: untrusted::Input<'a>)
            -> Result<(untrusted::Input<'a>, Option<untrusted::Input<'a>>),
                      error::Unspecified> {
        input.read_all(error::Unspecified, |input| {
            der::nested(input, der::Tag::Sequence, error::Unspecified, |input| {
                // Currently we only support algorithms that should only be encoded
                // in v1 form, so reject v2 and any later form.
                let require_public_key =
                        match (der::small_nonnegative_integer(input)?, version) {
                    (0, Version::V1Only) => false,
                    (0, Version::V1OrV2) => false,
                    (1, Version::V1OrV2) |
                    (1, Version::V2Only) => true,
                    _ => { return Err(error::Unspecified); }
                };

                let actual_alg_id =
                    der::expect_tag_and_get_value(input, der::Tag::Sequence)?;
                if actual_alg_id != alg_id {
                    return Err(error::Unspecified);
                }

                let private_key =
                    der::expect_tag_and_get_value(input, der::Tag::OctetString)?;

                // Ignore any attributes that are present.
                if input.peek(der::Tag::ContextSpecificConstructed0 as u8) {
                    let _ = der::expect_tag_and_get_value(input,
                        der::Tag::ContextSpecificConstructed0)?;
                }

                let public_key = if require_public_key {
                    Some(der::nested(
                        input, der::Tag::ContextSpecificConstructed1,
                        error::Unspecified, der::bit_string_with_no_unused_bits)?)
                } else {
                    None
                };

                Ok((private_key, public_key))
            })
        })
    }

    /// A generated PKCS#8 document.
    pub struct PKCS8Document {
        bytes: [u8; ec::PKCS8_DOCUMENT_MAX_LEN],
        len: usize,
    }

    impl AsRef<[u8]> for PKCS8Document {
        #[inline]
        fn as_ref(&self) -> &[u8] { &self.bytes[..self.len] }
    }

    pub fn wrap_key(template: &Template, private_key: &[u8], public_key: &[u8])
                    -> PKCS8Document {
        let mut result = PKCS8Document {
            bytes: [0; ec::PKCS8_DOCUMENT_MAX_LEN],
            len: template.bytes.len() + private_key.len() + public_key.len(),
        };
        wrap_key_(template, private_key, public_key, &mut result.bytes[..result.len]);
        result
    }

    /// Formats a private key "prefix||private_key||middle||public_key" where
    /// `template` is "prefix||middle" split at position `private_key_index`.
    pub fn wrap_key_(template: &Template, private_key: &[u8], public_key: &[u8],
                     bytes: &mut [u8]) {
        let (before_private_key, after_private_key) =
            template.bytes.split_at(template.private_key_index);
        let private_key_end_index = template.private_key_index + private_key.len();
        bytes[..template.private_key_index].copy_from_slice(before_private_key);
        bytes[template.private_key_index..private_key_end_index]
            .copy_from_slice(&private_key);
        bytes[private_key_end_index..
              (private_key_end_index + after_private_key.len())]
            .copy_from_slice(after_private_key);
        bytes[(private_key_end_index + after_private_key.len())..]
            .copy_from_slice(public_key);
    }

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