//! ChaCha20Poly1305 is an authenticated symmetric stream cipher based on chacha20 and poly1305

// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use crate::chacha20::ChaCha20;
use crate::cryptoutil::write_u64_le;
use crate::mac::Mac;
use crate::poly1305::Poly1305;
use crate::util::fixed_time_eq;

/// Chacha20Poly1305 Incremental Context for Authenticated Data (AAD)
#[derive(Clone)]
pub struct Context {
    cipher: ChaCha20,
    mac: Poly1305,
    aad_len: u64,
    data_len: u64,
}

/// ChaCha20Poly1305 Incremental Context for encryption
#[derive(Clone)]
pub struct ContextEncryption(Context);

/// ChaCha20Poly1305 Incremental Context for decryption
#[derive(Clone)]
pub struct ContextDecryption(Context);

/// ChaCha20Poly1305 Authenticated Tag (128 bits)
#[derive(Debug, Clone)]
pub struct Tag(pub [u8; 16]);

impl PartialEq for Tag {
    fn eq(&self, other: &Self) -> bool {
        fixed_time_eq(&self.0, &other.0)
    }
}

impl Eq for Tag {}

impl Context {
    /// Create a new context given the key and nonce
    pub fn new(key: &[u8], nonce: &[u8]) -> Self {
        assert!(key.len() == 16 || key.len() == 32);
        assert!(nonce.len() == 8 || nonce.len() == 12);
        let mut cipher = ChaCha20::new(key, nonce);
        let mut mac_key = [0u8; 64];
        let zero_key = [0u8; 64];
        cipher.process(&zero_key, &mut mac_key);

        let mac = Poly1305::new(&mac_key[..32]);
        Context {
            cipher: cipher,
            mac: mac,
            aad_len: 0,
            data_len: 0,
        }
    }

    fn add_encrypted(&mut self, encrypted: &[u8]) {
        self.mac.input(encrypted);
        self.data_len += encrypted.len() as u64;
    }

    /// Add Authenticated Data to the MAC Context
    ///
    /// This can be called multiple times
    pub fn add_data(&mut self, aad: &[u8]) {
        self.aad_len += aad.len() as u64;
        self.mac.input(aad);
    }

    /// Finish authenticated part and move to the encryption phase
    pub fn to_encryption(mut self) -> ContextEncryption {
        pad16(&mut self.mac, self.aad_len);
        ContextEncryption(self)
    }

    /// Finish authenticated part and move to the decryption phase
    pub fn to_decryption(mut self) -> ContextDecryption {
        pad16(&mut self.mac, self.aad_len);
        ContextDecryption(self)
    }
}

fn finalize_raw(inner: &mut Context) -> [u8; 16] {
    let mut len_buf = [0u8; 16];
    pad16(&mut inner.mac, inner.data_len);
    write_u64_le(&mut len_buf[0..8], inner.aad_len);
    write_u64_le(&mut len_buf[8..16], inner.data_len);
    inner.mac.input(&len_buf);
    inner.mac.raw_result(&mut len_buf);
    len_buf
}

impl ContextEncryption {
    /// Encrypt input in place
    pub fn encrypt_mut(&mut self, buf: &mut [u8]) {
        self.0.cipher.process_mut(buf);
        self.0.add_encrypted(buf);
    }

    /// Encrypt the input slice to the output slice
    ///
    /// Panics:
    ///     if input and output are of different size
    pub fn encrypt(&mut self, input: &[u8], output: &mut [u8]) {
        assert_eq!(input.len(), output.len());
        self.0.cipher.process(input, output);
        self.0.add_encrypted(output);
    }

    /// Finalize the encryption context and return the tag
    #[must_use]
    pub fn finalize(mut self) -> Tag {
        let tag = finalize_raw(&mut self.0);
        Tag(tag)
    }
}

/// Whether or not, the decryption was succesful related to the expected tag
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum DecryptionResult {
    Match,
    MisMatch,
}

impl ContextDecryption {
    /// Decrypt input in place
    pub fn decrypt_mut(&mut self, buf: &mut [u8]) {
        self.0.add_encrypted(buf);
        self.0.cipher.process_mut(buf);
    }

    /// Decrypt the input to the output slice
    ///
    /// Panics:
    ///     if input and output are of different size
    pub fn decrypt(&mut self, input: &[u8], output: &mut [u8]) {
        assert_eq!(input.len(), output.len());
        self.0.add_encrypted(input);
        self.0.cipher.process(input, output);
    }

    /// Finalize the decryption context and check that the tag match the expected value
    #[must_use]
    pub fn finalize(mut self, expected_tag: &Tag) -> DecryptionResult {
        let got_tag = Tag(finalize_raw(&mut self.0));
        if &got_tag == expected_tag {
            DecryptionResult::Match
        } else {
            DecryptionResult::MisMatch
        }
    }
}

/// A ChaCha20+Poly1305 Context
#[derive(Clone)]
pub struct ChaCha20Poly1305 {
    finished: bool,
    context: Context,
}

fn pad16(mac: &mut Poly1305, len: u64) {
    if (len % 16) != 0 {
        let padding = [0u8; 15];
        let sz = 16 - (len % 16) as usize;
        mac.input(&padding[0..sz]);
    }
}

impl ChaCha20Poly1305 {
    /// Create a new ChaCha20Poly1305
    ///
    /// * key needs to be 16 or 32 bytes
    /// * nonce needs to be 8 or 12 bytes
    pub fn new(key: &[u8], nonce: &[u8], aad: &[u8]) -> ChaCha20Poly1305 {
        let mut context = Context::new(key, nonce);
        context.add_data(aad);
        ChaCha20Poly1305 {
            context: context,
            finished: false,
        }
    }

    /// Encrypt input buffer to output buffer, and write an authenticated tag to out_tag.
    ///
    /// Output buffer need to be the same size as the input buffer
    /// Out_tag mutable slice need to 16 bytes exactly.
    pub fn encrypt(&mut self, input: &[u8], output: &mut [u8], out_tag: &mut [u8]) {
        assert!(input.len() == output.len());
        assert!(!self.finished);
        assert!(out_tag.len() == 16);

        self.finished = true;

        let mut ctx = self.context.clone().to_encryption();
        ctx.encrypt(input, output);

        let Tag(tag) = ctx.finalize();
        out_tag.copy_from_slice(&tag[..])
    }

    /// Decrypt the input to the output buffer
    ///
    /// if the calculated tag during decryption doesn't match
    /// the tag in parameter, then the function return False
    pub fn decrypt(&mut self, input: &[u8], output: &mut [u8], tag: &[u8]) -> bool {
        assert!(tag.len() == 16);
        assert!(input.len() == output.len());
        assert!(!self.finished);

        self.finished = true;

        let mut tag_data = [0u8; 16];
        tag_data.copy_from_slice(tag);

        let mut ctx = self.context.clone().to_decryption();

        ctx.decrypt(input, output);
        ctx.finalize(&Tag(tag_data)) == DecryptionResult::Match
    }
}

#[cfg(test)]
mod test {
    use super::ChaCha20Poly1305;
    use std::vec::Vec;

    struct TestVector {
        key: [u8; 32],
        nonce: &'static [u8],
        tag: [u8; 16],
        plain_text: Vec<u8>,
        cipher_text: Vec<u8>,
        aad: Vec<u8>,
    }

    fn test_vector(v: &TestVector) {
        let mut tag = [0u8; 16];
        let mut ciphertext = vec![0u8; v.cipher_text.len()];

        let mut context = ChaCha20Poly1305::new(&v.key, &v.nonce, &v.aad);
        let mut dcontext = context.clone();

        // test encryption
        context.encrypt(&v.plain_text, &mut ciphertext, &mut tag[..]);

        assert_eq!(&ciphertext[..], &v.cipher_text[..]);
        assert_eq!(&tag[..], &v.tag[..]);

        // test decryption
        let mut output = vec![0u8; v.plain_text.len()];
        assert!(dcontext.decrypt(&ciphertext, &mut output, &v.tag[..]), true);

        assert_eq!(&output[..], &v.plain_text[..]);
    }

    #[test]
    fn test_vectors() {
        let tests = [
            // RFC 7539 section 2.8.2.
            TestVector {
                key: [
                    0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x8b, 0x8c,
                    0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99,
                    0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
                ],
                nonce: &[
                    0x07, 0x00, 0x00, 0x00, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
                ],
                plain_text: vec![
                    0x4c, 0x61, 0x64, 0x69, 0x65, 0x73, 0x20, 0x61, 0x6e, 0x64, 0x20, 0x47, 0x65,
                    0x6e, 0x74, 0x6c, 0x65, 0x6d, 0x65, 0x6e, 0x20, 0x6f, 0x66, 0x20, 0x74, 0x68,
                    0x65, 0x20, 0x63, 0x6c, 0x61, 0x73, 0x73, 0x20, 0x6f, 0x66, 0x20, 0x27, 0x39,
                    0x39, 0x3a, 0x20, 0x49, 0x66, 0x20, 0x49, 0x20, 0x63, 0x6f, 0x75, 0x6c, 0x64,
                    0x20, 0x6f, 0x66, 0x66, 0x65, 0x72, 0x20, 0x79, 0x6f, 0x75, 0x20, 0x6f, 0x6e,
                    0x6c, 0x79, 0x20, 0x6f, 0x6e, 0x65, 0x20, 0x74, 0x69, 0x70, 0x20, 0x66, 0x6f,
                    0x72, 0x20, 0x74, 0x68, 0x65, 0x20, 0x66, 0x75, 0x74, 0x75, 0x72, 0x65, 0x2c,
                    0x20, 0x73, 0x75, 0x6e, 0x73, 0x63, 0x72, 0x65, 0x65, 0x6e, 0x20, 0x77, 0x6f,
                    0x75, 0x6c, 0x64, 0x20, 0x62, 0x65, 0x20, 0x69, 0x74, 0x2e,
                ],
                aad: vec![
                    0x50, 0x51, 0x52, 0x53, 0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
                ],
                cipher_text: vec![
                    0xd3, 0x1a, 0x8d, 0x34, 0x64, 0x8e, 0x60, 0xdb, 0x7b, 0x86, 0xaf, 0xbc, 0x53,
                    0xef, 0x7e, 0xc2, 0xa4, 0xad, 0xed, 0x51, 0x29, 0x6e, 0x08, 0xfe, 0xa9, 0xe2,
                    0xb5, 0xa7, 0x36, 0xee, 0x62, 0xd6, 0x3d, 0xbe, 0xa4, 0x5e, 0x8c, 0xa9, 0x67,
                    0x12, 0x82, 0xfa, 0xfb, 0x69, 0xda, 0x92, 0x72, 0x8b, 0x1a, 0x71, 0xde, 0x0a,
                    0x9e, 0x06, 0x0b, 0x29, 0x05, 0xd6, 0xa5, 0xb6, 0x7e, 0xcd, 0x3b, 0x36, 0x92,
                    0xdd, 0xbd, 0x7f, 0x2d, 0x77, 0x8b, 0x8c, 0x98, 0x03, 0xae, 0xe3, 0x28, 0x09,
                    0x1b, 0x58, 0xfa, 0xb3, 0x24, 0xe4, 0xfa, 0xd6, 0x75, 0x94, 0x55, 0x85, 0x80,
                    0x8b, 0x48, 0x31, 0xd7, 0xbc, 0x3f, 0xf4, 0xde, 0xf0, 0x8e, 0x4b, 0x7a, 0x9d,
                    0xe5, 0x76, 0xd2, 0x65, 0x86, 0xce, 0xc6, 0x4b, 0x61, 0x16,
                ],
                tag: [
                    0x1a, 0xe1, 0x0b, 0x59, 0x4f, 0x09, 0xe2, 0x6a, 0x7e, 0x90, 0x2e, 0xcb, 0xd0,
                    0x60, 0x06, 0x91,
                ],
            },
            // RFC 7539 section A.5.
            TestVector {
                key: [
                    0x1c, 0x92, 0x40, 0xa5, 0xeb, 0x55, 0xd3, 0x8a, 0xf3, 0x33, 0x88, 0x86, 0x04,
                    0xf6, 0xb5, 0xf0, 0x47, 0x39, 0x17, 0xc1, 0x40, 0x2b, 0x80, 0x09, 0x9d, 0xca,
                    0x5c, 0xbc, 0x20, 0x70, 0x75, 0xc0,
                ],
                nonce: &[
                    0x00, 0x00, 0x00, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
                ],
                tag: [
                    0xee, 0xad, 0x9d, 0x67, 0x89, 0x0c, 0xbb, 0x22, 0x39, 0x23, 0x36, 0xfe, 0xa1,
                    0x85, 0x1f, 0x38,
                ],
                plain_text: vec![
                    0x49, 0x6e, 0x74, 0x65, 0x72, 0x6e, 0x65, 0x74, 0x2d, 0x44, 0x72, 0x61, 0x66,
                    0x74, 0x73, 0x20, 0x61, 0x72, 0x65, 0x20, 0x64, 0x72, 0x61, 0x66, 0x74, 0x20,
                    0x64, 0x6f, 0x63, 0x75, 0x6d, 0x65, 0x6e, 0x74, 0x73, 0x20, 0x76, 0x61, 0x6c,
                    0x69, 0x64, 0x20, 0x66, 0x6f, 0x72, 0x20, 0x61, 0x20, 0x6d, 0x61, 0x78, 0x69,
                    0x6d, 0x75, 0x6d, 0x20, 0x6f, 0x66, 0x20, 0x73, 0x69, 0x78, 0x20, 0x6d, 0x6f,
                    0x6e, 0x74, 0x68, 0x73, 0x20, 0x61, 0x6e, 0x64, 0x20, 0x6d, 0x61, 0x79, 0x20,
                    0x62, 0x65, 0x20, 0x75, 0x70, 0x64, 0x61, 0x74, 0x65, 0x64, 0x2c, 0x20, 0x72,
                    0x65, 0x70, 0x6c, 0x61, 0x63, 0x65, 0x64, 0x2c, 0x20, 0x6f, 0x72, 0x20, 0x6f,
                    0x62, 0x73, 0x6f, 0x6c, 0x65, 0x74, 0x65, 0x64, 0x20, 0x62, 0x79, 0x20, 0x6f,
                    0x74, 0x68, 0x65, 0x72, 0x20, 0x64, 0x6f, 0x63, 0x75, 0x6d, 0x65, 0x6e, 0x74,
                    0x73, 0x20, 0x61, 0x74, 0x20, 0x61, 0x6e, 0x79, 0x20, 0x74, 0x69, 0x6d, 0x65,
                    0x2e, 0x20, 0x49, 0x74, 0x20, 0x69, 0x73, 0x20, 0x69, 0x6e, 0x61, 0x70, 0x70,
                    0x72, 0x6f, 0x70, 0x72, 0x69, 0x61, 0x74, 0x65, 0x20, 0x74, 0x6f, 0x20, 0x75,
                    0x73, 0x65, 0x20, 0x49, 0x6e, 0x74, 0x65, 0x72, 0x6e, 0x65, 0x74, 0x2d, 0x44,
                    0x72, 0x61, 0x66, 0x74, 0x73, 0x20, 0x61, 0x73, 0x20, 0x72, 0x65, 0x66, 0x65,
                    0x72, 0x65, 0x6e, 0x63, 0x65, 0x20, 0x6d, 0x61, 0x74, 0x65, 0x72, 0x69, 0x61,
                    0x6c, 0x20, 0x6f, 0x72, 0x20, 0x74, 0x6f, 0x20, 0x63, 0x69, 0x74, 0x65, 0x20,
                    0x74, 0x68, 0x65, 0x6d, 0x20, 0x6f, 0x74, 0x68, 0x65, 0x72, 0x20, 0x74, 0x68,
                    0x61, 0x6e, 0x20, 0x61, 0x73, 0x20, 0x2f, 0xe2, 0x80, 0x9c, 0x77, 0x6f, 0x72,
                    0x6b, 0x20, 0x69, 0x6e, 0x20, 0x70, 0x72, 0x6f, 0x67, 0x72, 0x65, 0x73, 0x73,
                    0x2e, 0x2f, 0xe2, 0x80, 0x9d,
                ],
                cipher_text: vec![
                    0x64, 0xa0, 0x86, 0x15, 0x75, 0x86, 0x1a, 0xf4, 0x60, 0xf0, 0x62, 0xc7, 0x9b,
                    0xe6, 0x43, 0xbd, 0x5e, 0x80, 0x5c, 0xfd, 0x34, 0x5c, 0xf3, 0x89, 0xf1, 0x08,
                    0x67, 0x0a, 0xc7, 0x6c, 0x8c, 0xb2, 0x4c, 0x6c, 0xfc, 0x18, 0x75, 0x5d, 0x43,
                    0xee, 0xa0, 0x9e, 0xe9, 0x4e, 0x38, 0x2d, 0x26, 0xb0, 0xbd, 0xb7, 0xb7, 0x3c,
                    0x32, 0x1b, 0x01, 0x00, 0xd4, 0xf0, 0x3b, 0x7f, 0x35, 0x58, 0x94, 0xcf, 0x33,
                    0x2f, 0x83, 0x0e, 0x71, 0x0b, 0x97, 0xce, 0x98, 0xc8, 0xa8, 0x4a, 0xbd, 0x0b,
                    0x94, 0x81, 0x14, 0xad, 0x17, 0x6e, 0x00, 0x8d, 0x33, 0xbd, 0x60, 0xf9, 0x82,
                    0xb1, 0xff, 0x37, 0xc8, 0x55, 0x97, 0x97, 0xa0, 0x6e, 0xf4, 0xf0, 0xef, 0x61,
                    0xc1, 0x86, 0x32, 0x4e, 0x2b, 0x35, 0x06, 0x38, 0x36, 0x06, 0x90, 0x7b, 0x6a,
                    0x7c, 0x02, 0xb0, 0xf9, 0xf6, 0x15, 0x7b, 0x53, 0xc8, 0x67, 0xe4, 0xb9, 0x16,
                    0x6c, 0x76, 0x7b, 0x80, 0x4d, 0x46, 0xa5, 0x9b, 0x52, 0x16, 0xcd, 0xe7, 0xa4,
                    0xe9, 0x90, 0x40, 0xc5, 0xa4, 0x04, 0x33, 0x22, 0x5e, 0xe2, 0x82, 0xa1, 0xb0,
                    0xa0, 0x6c, 0x52, 0x3e, 0xaf, 0x45, 0x34, 0xd7, 0xf8, 0x3f, 0xa1, 0x15, 0x5b,
                    0x00, 0x47, 0x71, 0x8c, 0xbc, 0x54, 0x6a, 0x0d, 0x07, 0x2b, 0x04, 0xb3, 0x56,
                    0x4e, 0xea, 0x1b, 0x42, 0x22, 0x73, 0xf5, 0x48, 0x27, 0x1a, 0x0b, 0xb2, 0x31,
                    0x60, 0x53, 0xfa, 0x76, 0x99, 0x19, 0x55, 0xeb, 0xd6, 0x31, 0x59, 0x43, 0x4e,
                    0xce, 0xbb, 0x4e, 0x46, 0x6d, 0xae, 0x5a, 0x10, 0x73, 0xa6, 0x72, 0x76, 0x27,
                    0x09, 0x7a, 0x10, 0x49, 0xe6, 0x17, 0xd9, 0x1d, 0x36, 0x10, 0x94, 0xfa, 0x68,
                    0xf0, 0xff, 0x77, 0x98, 0x71, 0x30, 0x30, 0x5b, 0xea, 0xba, 0x2e, 0xda, 0x04,
                    0xdf, 0x99, 0x7b, 0x71, 0x4d, 0x6c, 0x6f, 0x2c, 0x29, 0xa6, 0xad, 0x5c, 0xb4,
                    0x02, 0x2b, 0x02, 0x70, 0x9b,
                ],
                aad: vec![
                    0xf3, 0x33, 0x88, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x4e, 0x91,
                ],
            },
        ];
        for tv in tests.iter() {
            test_vector(&tv)
        }
    }
}

#[cfg(all(test, feature = "with-bench"))]
mod bench {
    use super::ChaCha20Poly1305;
    use test::Bencher;

    #[bench]
    pub fn chacha20poly1305_10(bh: &mut Bencher) {
        let input = [1u8; 10];
        let aad = [3u8; 10];
        bh.iter(|| {
            let mut cipher = ChaCha20Poly1305::new(&[0; 32], &[0; 8], &aad);
            let mut decipher = ChaCha20Poly1305::new(&[0; 32], &[0; 8], &aad);

            let mut output = [0u8; 10];
            let mut tag = [0u8; 16];
            let mut output2 = [0u8; 10];
            cipher.encrypt(&input, &mut output, &mut tag);
            decipher.decrypt(&output, &mut output2, &tag);
        });
        bh.bytes = 10u64;
    }

    #[bench]
    pub fn chacha20poly1305_1k(bh: &mut Bencher) {
        let input = [1u8; 1024];
        let aad = [3u8; 1024];
        bh.iter(|| {
            let mut cipher = ChaCha20Poly1305::new(&[0; 32], &[0; 8], &aad);
            let mut decipher = ChaCha20Poly1305::new(&[0; 32], &[0; 8], &aad);

            let mut output = [0u8; 1024];
            let mut tag = [0u8; 16];
            let mut output2 = [0u8; 1024];

            cipher.encrypt(&input, &mut output, &mut tag);
            decipher.decrypt(&output, &mut output2, &tag);
        });
        bh.bytes = 1024u64;
    }

    #[bench]
    pub fn chacha20poly1305_64k(bh: &mut Bencher) {
        let input = [1u8; 65536];
        let aad = [3u8; 65536];
        bh.iter(|| {
            let mut cipher = ChaCha20Poly1305::new(&[0; 32], &[0; 8], &aad);
            let mut decipher = ChaCha20Poly1305::new(&[0; 32], &[0; 8], &aad);

            let mut output = [0u8; 65536];
            let mut tag = [0u8; 16];
            let mut output2 = [0u8; 65536];

            cipher.encrypt(&input, &mut output, &mut tag);
            decipher.decrypt(&output, &mut output2, &tag);
        });
        bh.bytes = 65536u64;
    }
}