// 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 crate::{ec, error, io::der};

pub(crate) struct PublicKeyOptions {

    /// Should the wrong public key ASN.1 tagging used by early implementations

    /// of PKCS#8 v2 (including earlier versions of *ring*) be accepted?

    pub accept_legacy_ed25519_public_key_tag: bool,

}

pub(crate) enum Version {

    V1Only,

    V1OrV2(PublicKeyOptions),

    V2Only(PublicKeyOptions),

}

/// A template for constructing PKCS#8 documents.

///

/// Note that this only works for ECC.

pub(crate) 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) -> untrusted::Input {

        untrusted::Input::from(self.alg_id_value_())

    }

    fn alg_id_value_(&self) -> &[u8] {

        &self.bytes[self.alg_id_range.start..self.alg_id_range.end]

    }

    #[inline]

    pub fn curve_oid(&self) -> untrusted::Input {

        untrusted::Input::from(&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(crate) fn unwrap_key<'a>(

    template: &Template,

    version: Version,

    input: untrusted::Input<'a>,

) -> Result<(untrusted::Input<'a>, Option<untrusted::Input<'a>>), error::KeyRejected> {

    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(crate) fn unwrap_key_<'a>(

    alg_id: untrusted::Input,

    version: Version,

    input: untrusted::Input<'a>,

) -> Result<(untrusted::Input<'a>, Option<untrusted::Input<'a>>), error::KeyRejected> {

    input.read_all(error::KeyRejected::invalid_encoding(), |input| {

        der::nested(

            input,

            der::Tag::Sequence,

            error::KeyRejected::invalid_encoding(),

            |input| unwrap_key__(alg_id, version, input),

        )

    })

}

fn unwrap_key__<'a>(

    alg_id: untrusted::Input,

    version: Version,

    input: &mut untrusted::Reader<'a>,

) -> Result<(untrusted::Input<'a>, Option<untrusted::Input<'a>>), error::KeyRejected> {

    let actual_version = der::small_nonnegative_integer(input)

        .map_err(|error::Unspecified| error::KeyRejected::invalid_encoding())?;

    // Do things in a specific order to return more useful errors:

    // 1. Check for completely unsupported version.

    // 2. Check for algorithm mismatch.

    // 3. Check for algorithm-specific version mismatch.

    if actual_version > 1 {

        return Err(error::KeyRejected::version_not_supported());

    };

    let actual_alg_id = der::expect_tag_and_get_value(input, der::Tag::Sequence)

        .map_err(|error::Unspecified| error::KeyRejected::invalid_encoding())?;

    if actual_alg_id.as_slice_less_safe() != alg_id.as_slice_less_safe() {

        return Err(error::KeyRejected::wrong_algorithm());

    }

    let public_key_options = match (actual_version, version) {

        (0, Version::V1Only) => None,

        (0, Version::V1OrV2(_)) => None,

        (1, Version::V1OrV2(options)) | (1, Version::V2Only(options)) => Some(options),

        _ => {

            return Err(error::KeyRejected::version_not_supported());

        }

    };

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

        .map_err(|error::Unspecified| error::KeyRejected::invalid_encoding())?;

    // 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)

            .map_err(|error::Unspecified| error::KeyRejected::invalid_encoding())?;

    }

    let public_key = if let Some(options) = public_key_options {

        if input.at_end() {

            return Err(error::KeyRejected::public_key_is_missing());

        }

        const INCORRECT_LEGACY: der::Tag = der::Tag::ContextSpecificConstructed1;

        let result =

            if options.accept_legacy_ed25519_public_key_tag && input.peek(INCORRECT_LEGACY as u8) {

                der::nested(

                    input,

                    INCORRECT_LEGACY,

                    error::Unspecified,

                    der::bit_string_with_no_unused_bits,

                )

            } else {

                der::bit_string_tagged_with_no_unused_bits(der::Tag::ContextSpecific1, input)

            };

        let public_key =

            result.map_err(|error::Unspecified| error::KeyRejected::invalid_encoding())?;

        Some(public_key)

    } else {

        None

    };

    Ok((private_key, public_key))

}

/// A generated PKCS#8 document.

pub struct Document {

    bytes: [u8; ec::PKCS8_DOCUMENT_MAX_LEN],

    len: usize,

}

impl AsRef<[u8]> for Document {

    #[inline]

    fn as_ref(&self) -> &[u8] {

        &self.bytes[..self.len]

    }

}

pub(crate) fn wrap_key(template: &Template, private_key: &[u8], public_key: &[u8]) -> Document {

    let mut result = Document {

        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`.

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);

}