//! Implementation of the ZipCrypto algorithm
//!
//! The following paper was used to implement the ZipCrypto algorithm:
//! [https://courses.cs.ut.ee/MTAT.07.022/2015_fall/uploads/Main/dmitri-report-f15-16.pdf](https://courses.cs.ut.ee/MTAT.07.022/2015_fall/uploads/Main/dmitri-report-f15-16.pdf)

use std::num::Wrapping;

/// A container to hold the current key state
struct ZipCryptoKeys {
    key_0: Wrapping<u32>,
    key_1: Wrapping<u32>,
    key_2: Wrapping<u32>,
}

impl ZipCryptoKeys {
    fn new() -> ZipCryptoKeys {
        ZipCryptoKeys {
            key_0: Wrapping(0x12345678),
            key_1: Wrapping(0x23456789),
            key_2: Wrapping(0x34567890),
        }
    }

    fn update(&mut self, input: u8) {
        self.key_0 = ZipCryptoKeys::crc32(self.key_0, input);
        self.key_1 =
            (self.key_1 + (self.key_0 & Wrapping(0xff))) * Wrapping(0x08088405) + Wrapping(1);
        self.key_2 = ZipCryptoKeys::crc32(self.key_2, (self.key_1 >> 24).0 as u8);
    }

    fn stream_byte(&mut self) -> u8 {
        let temp: Wrapping<u16> = Wrapping(self.key_2.0 as u16) | Wrapping(3);
        ((temp * (temp ^ Wrapping(1))) >> 8).0 as u8
    }

    fn decrypt_byte(&mut self, cipher_byte: u8) -> u8 {
        let plain_byte: u8 = self.stream_byte() ^ cipher_byte;
        self.update(plain_byte);
        plain_byte
    }

    #[allow(dead_code)]
    fn encrypt_byte(&mut self, plain_byte: u8) -> u8 {
        let cipher_byte: u8 = self.stream_byte() ^ plain_byte;
        self.update(plain_byte);
        cipher_byte
    }

    fn crc32(crc: Wrapping<u32>, input: u8) -> Wrapping<u32> {
        (crc >> 8) ^ Wrapping(CRCTABLE[((crc & Wrapping(0xff)).0 as u8 ^ input) as usize])
    }
}

/// A ZipCrypto reader with unverified password
pub struct ZipCryptoReader<R> {
    file: R,
    keys: ZipCryptoKeys,
}

pub enum ZipCryptoValidator {
    PkzipCrc32(u32),
    InfoZipMsdosTime(u16),
}

impl<R: std::io::Read> ZipCryptoReader<R> {
    /// Note: The password is `&[u8]` and not `&str` because the
    /// [zip specification](https://pkware.cachefly.net/webdocs/APPNOTE/APPNOTE-6.3.3.TXT)
    /// does not specify password encoding (see function `update_keys` in the specification).
    /// Therefore, if `&str` was used, the password would be UTF-8 and it
    /// would be impossible to decrypt files that were encrypted with a
    /// password byte sequence that is unrepresentable in UTF-8.
    pub fn new(file: R, password: &[u8]) -> ZipCryptoReader<R> {
        let mut result = ZipCryptoReader {
            file,
            keys: ZipCryptoKeys::new(),
        };

        // Key the cipher by updating the keys with the password.
        for byte in password.iter() {
            result.keys.update(*byte);
        }

        result
    }

    /// Read the ZipCrypto header bytes and validate the password.
    pub fn validate(
        mut self,
        validator: ZipCryptoValidator,
    ) -> Result<Option<ZipCryptoReaderValid<R>>, std::io::Error> {
        // ZipCrypto prefixes a file with a 12 byte header
        let mut header_buf = [0u8; 12];
        self.file.read_exact(&mut header_buf)?;
        for byte in header_buf.iter_mut() {
            *byte = self.keys.decrypt_byte(*byte);
        }

        match validator {
            ZipCryptoValidator::PkzipCrc32(crc32_plaintext) => {
                // PKZIP before 2.0 used 2 byte CRC check.
                // PKZIP 2.0+ used 1 byte CRC check. It's more secure.
                // We also use 1 byte CRC.

                if (crc32_plaintext >> 24) as u8 != header_buf[11] {
                    return Ok(None); // Wrong password
                }
            }
            ZipCryptoValidator::InfoZipMsdosTime(last_mod_time) => {
                // Info-ZIP modification to ZipCrypto format:
                // If bit 3 of the general purpose bit flag is set
                // (indicates that the file uses a data-descriptor section),
                // it uses high byte of 16-bit File Time.
                // Info-ZIP code probably writes 2 bytes of File Time.
                // We check only 1 byte.

                if (last_mod_time >> 8) as u8 != header_buf[11] {
                    return Ok(None); // Wrong password
                }
            }
        }

        Ok(Some(ZipCryptoReaderValid { reader: self }))
    }
}

/// A ZipCrypto reader with verified password
pub struct ZipCryptoReaderValid<R> {
    reader: ZipCryptoReader<R>,
}

impl<R: std::io::Read> std::io::Read for ZipCryptoReaderValid<R> {
    fn read(&mut self, mut buf: &mut [u8]) -> std::io::Result<usize> {
        // Note: There might be potential for optimization. Inspiration can be found at:
        // https://github.com/kornelski/7z/blob/master/CPP/7zip/Crypto/ZipCrypto.cpp

        let result = self.reader.file.read(&mut buf);
        for byte in buf.iter_mut() {
            *byte = self.reader.keys.decrypt_byte(*byte);
        }
        result
    }
}

impl<R: std::io::Read> ZipCryptoReaderValid<R> {
    /// Consumes this decoder, returning the underlying reader.
    pub fn into_inner(self) -> R {
        self.reader.file
    }
}

static CRCTABLE: [u32; 256] = [
    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
    0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
    0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
    0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
    0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
    0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
    0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
    0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
    0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
    0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
    0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
    0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
    0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
    0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
    0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
    0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
    0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
    0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d,
];
