// Copyright 2015-2016 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 AUTHOR DISCLAIMS ALL WARRANTIES

// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR 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.

use crate::{bb, bits, digest, error, rand};

mod pkcs1;

mod pss;

pub use self::{

    pkcs1::{RSA_PKCS1_SHA256, RSA_PKCS1_SHA384, RSA_PKCS1_SHA512},

    pss::{RSA_PSS_SHA256, RSA_PSS_SHA384, RSA_PSS_SHA512},

};

pub(super) use pkcs1::RSA_PKCS1_SHA1_FOR_LEGACY_USE_ONLY;

/// Common features of both RSA padding encoding and RSA padding verification.

pub trait Padding: 'static + Sync + crate::sealed::Sealed + core::fmt::Debug {

    // The digest algorithm used for digesting the message (and maybe for

    // other things).

    fn digest_alg(&self) -> &'static digest::Algorithm;

}

/// An RSA signature encoding as described in [RFC 3447 Section 8].

///

/// [RFC 3447 Section 8]: https://tools.ietf.org/html/rfc3447#section-8

#[cfg(feature = "alloc")]

pub trait RsaEncoding: Padding {

    #[doc(hidden)]

    fn encode(

        &self,

        m_hash: digest::Digest,

        m_out: &mut [u8],

        mod_bits: bits::BitLength,

        rng: &dyn rand::SecureRandom,

    ) -> Result<(), error::Unspecified>;

}

/// Verification of an RSA signature encoding as described in

/// [RFC 3447 Section 8].

///

/// [RFC 3447 Section 8]: https://tools.ietf.org/html/rfc3447#section-8

pub trait Verification: Padding {

    fn verify(

        &self,

        m_hash: digest::Digest,

        m: &mut untrusted::Reader,

        mod_bits: bits::BitLength,

    ) -> Result<(), error::Unspecified>;

}

// Masks `out` with the output of the mask-generating function MGF1 as

// described in https://tools.ietf.org/html/rfc3447#appendix-B.2.1.

fn mgf1(digest_alg: &'static digest::Algorithm, seed: &[u8], out: &mut [u8]) {

    let digest_len = digest_alg.output_len();

    // Maximum counter value is the value of (mask_len / digest_len) rounded up.

    for (i, out) in out.chunks_mut(digest_len).enumerate() {

        let mut ctx = digest::Context::new(digest_alg);

        ctx.update(seed);

        // The counter will always fit in a `u32` because we reject absurdly

        // long inputs very early.

        ctx.update(&u32::to_be_bytes(i.try_into().unwrap()));

        let digest = ctx.finish();

        // The last chunk may legitimately be shorter than `digest`, but

        // `digest` will never be shorter than `out`.

        bb::xor_assign_at_start(out, digest.as_ref());

    }

}

#[cfg(test)]

mod test {

    use super::*;

    use crate::{digest, error, test};

    use alloc::vec;

    #[test]

    fn test_pss_padding_verify() {

        test::run(

            test_file!("rsa_pss_padding_tests.txt"),

            |section, test_case| {

                assert_eq!(section, "");

                let digest_name = test_case.consume_string("Digest");

                let alg = match digest_name.as_ref() {

                    "SHA256" => &RSA_PSS_SHA256,

                    "SHA384" => &RSA_PSS_SHA384,

                    "SHA512" => &RSA_PSS_SHA512,

                    _ => panic!("Unsupported digest: {}", digest_name),

                };

                let msg = test_case.consume_bytes("Msg");

                let msg = untrusted::Input::from(&msg);

                let m_hash = digest::digest(alg.digest_alg(), msg.as_slice_less_safe());

                let encoded = test_case.consume_bytes("EM");

                let encoded = untrusted::Input::from(&encoded);

                // Salt is recomputed in verification algorithm.

                let _ = test_case.consume_bytes("Salt");

                let bit_len = test_case.consume_usize_bits("Len");

                let is_valid = test_case.consume_string("Result") == "P";

                let actual_result =

                    encoded.read_all(error::Unspecified, |m| alg.verify(m_hash, m, bit_len));

                assert_eq!(actual_result.is_ok(), is_valid);

                Ok(())

            },

        );

    }

    // Tests PSS encoding for various public modulus lengths.

    #[cfg(feature = "alloc")]

    #[test]

    fn test_pss_padding_encode() {

        test::run(

            test_file!("rsa_pss_padding_tests.txt"),

            |section, test_case| {

                assert_eq!(section, "");

                let digest_name = test_case.consume_string("Digest");

                let alg = match digest_name.as_ref() {

                    "SHA256" => &RSA_PSS_SHA256,

                    "SHA384" => &RSA_PSS_SHA384,

                    "SHA512" => &RSA_PSS_SHA512,

                    _ => panic!("Unsupported digest: {}", digest_name),

                };

                let msg = test_case.consume_bytes("Msg");

                let salt = test_case.consume_bytes("Salt");

                let encoded = test_case.consume_bytes("EM");

                let bit_len = test_case.consume_usize_bits("Len");

                let expected_result = test_case.consume_string("Result");

                // Only test the valid outputs

                if expected_result != "P" {

                    return Ok(());

                }

                let rng = test::rand::FixedSliceRandom { bytes: &salt };

                let mut m_out = vec![0u8; bit_len.as_usize_bytes_rounded_up()];

                let digest = digest::digest(alg.digest_alg(), &msg);

                alg.encode(digest, &mut m_out, bit_len, &rng).unwrap();

                assert_eq!(m_out, encoded);

                Ok(())

            },

        );

    }

}