feat: first version

src/lib.rs

@@ -0,0 +1,8 @@
+//! _Tencent modified TEA_ (tc_tea) is a variant of the standard TEA (Tiny Encryption Algorithm).
+//! Notably, it uses a different round number and uses a "tweaked" CBC mode.
+
+mod stream_ext;
+mod tc_tea;
+mod tc_tea_internal;
+
+pub use tc_tea::*;

src/stream_ext.rs

@@ -0,0 +1,84 @@
+pub trait StreamExt {
+    fn read_u32_be(&self, offset: usize) -> u32;
+    fn write_u32_be(&mut self, offset: usize, value: u32);
+    fn xor_block(&mut self, dst_offset: usize, size: usize, src: &[u8], src_offset: usize);
+    fn is_all_zeros(&self) -> bool;
+
+    fn xor_prev_tea_block(&mut self, offset: usize);
+    fn copy_tea_block(&mut self, offset: usize, src: &[u8], src_offset: usize);
+    fn xor_tea_block(&mut self, dst_offset: usize, src: &[u8], src_offset: usize);
+}
+
+impl StreamExt for [u8] {
+    #[inline]
+    fn read_u32_be(&self, offset: usize) -> u32 {
+        (u32::from(self[offset]) << 24)
+            | (u32::from(self[offset + 1]) << 16)
+            | (u32::from(self[offset + 2]) << 8)
+            | (u32::from(self[offset + 3]))
+    }
+
+    #[inline]
+    fn write_u32_be(&mut self, offset: usize, value: u32) {
+        self[offset..offset + 4].copy_from_slice(&value.to_be_bytes());
+    }
+
+    #[inline]
+    fn xor_block(&mut self, dst_offset: usize, size: usize, src: &[u8], src_offset: usize) {
+        for i in 0..size {
+            self[dst_offset + i] ^= src[src_offset + i];
+        }
+    }
+
+    /// Constant time all zero comparison
+    /// Attempts to do constant time comparison,
+    ///   but probably gets optimised away by llvm... lol
+    fn is_all_zeros(&self) -> bool {
+        let mut sum = 0;
+
+        for b in self {
+            sum |= b;
+        }
+
+        return sum == 0;
+    }
+
+    #[inline]
+    fn xor_prev_tea_block(&mut self, offset: usize) {
+        for i in offset..offset + 8 {
+            self[i] ^= self[i - 8];
+        }
+    }
+
+    #[inline]
+    fn copy_tea_block(&mut self, offset: usize, src: &[u8], src_offset: usize) {
+        self[offset..offset + 8]
+            .as_mut()
+            .copy_from_slice(&src[src_offset..src_offset + 8]);
+    }
+
+    #[inline]
+    fn xor_tea_block(&mut self, dst_offset: usize, src: &[u8], src_offset: usize) {
+        self.xor_block(dst_offset, 8, src, src_offset);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_read_u32_be() {
+        let v1 = [1, 2, 3, 4];
+        let v2 = [0x7f, 0xff, 0xee, 0xdd, 0xcc];
+        assert_eq!(v1.read_u32_be(0), 0x01020304);
+        assert_eq!(v2.read_u32_be(1), 0xffeeddcc);
+    }
+
+    #[test]
+    fn test_write_u32_be() {
+        let v2 = &mut [0x7fu8, 0xff, 0xee, 0xdd, 0xcc];
+        v2.write_u32_be(0, 0x01020304);
+        assert_eq!(v2, &[1u8, 2, 3, 4, 0xcc]);
+    }
+}

src/tc_tea.rs

@@ -0,0 +1,175 @@
+use rand::prelude::*;
+use rand_chacha::ChaCha20Rng;
+
+use super::stream_ext::StreamExt;
+use super::tc_tea_internal::{ecb_decrypt, ecb_encrypt, parse_key};
+
+const SALT_LEN: usize = 2;
+const ZERO_LEN: usize = 7;
+const FIXED_PADDING_LEN: usize = 1 + SALT_LEN + ZERO_LEN;
+
+pub fn calc_encrypted_size(body_size: usize) -> usize {
+    let len = FIXED_PADDING_LEN + body_size;
+    let pad_len = (8 - (len & 0b0111)) & 0b0111;
+    len + pad_len
+}
+
+/// Encrypts an arbitrary length sized data in the following way:
+/// * PadLen  (1 byte)
+/// * Padding (variable, 0-7byte)
+/// * Salt    (2 bytes)
+/// * Body    (? bytes)
+/// * Zero    (7 bytes)
+/// PadLen/Padding/Salt is random bytes. Minimum of 3 bytes.
+/// PadLen is taken from the last 3 bit of the first byte.
+///
+/// # Panics
+///
+/// If random number generator fails, it will panic.
+pub fn encrypt<T: AsRef<[u8]>, K: AsRef<[u8]>>(plaintext: T, key: K) -> Option<Box<[u8]>> {
+    let plaintext = plaintext.as_ref();
+    let key = parse_key(key.as_ref())?;
+
+    // buffer size calculation
+    let len = FIXED_PADDING_LEN + plaintext.len();
+    let pad_len = (8 - (len & 0b0111)) & 0b0111;
+    let len = len + pad_len; // add our padding
+    debug_assert_eq!(
+        len,
+        calc_encrypted_size(plaintext.len()),
+        "encrypted size calculation mismatch"
+    );
+    let header_len = 1 + pad_len + SALT_LEN;
+
+    // Setup buffer
+    let mut encrypted = vec![0u8; len].into_boxed_slice();
+    let mut iv1 = vec![0u8; len].into_boxed_slice();
+
+    // Setup a header with random padding/salt
+    #[cfg(feature = "secure_random")]
+    ChaCha20Rng::from_entropy().fill_bytes(&mut encrypted[0..header_len]);
+
+    #[cfg(not(feature = "secure_random"))]
+    ChaCha20Rng::from_rng(thread_rng())
+        .unwrap()
+        .fill_bytes(&mut encrypted[0..header_len]);
+
+    encrypted[0] = (encrypted[0] & 0b1111_1100) | ((pad_len as u8) & 0b0000_0111);
+
+    // Copy input to destination buffer.
+    encrypted[header_len..header_len + plaintext.len()]
+        .as_mut()
+        .copy_from_slice(plaintext);
+
+    // First block
+    iv1.copy_tea_block(0, &encrypted, 0); // preserve iv2 for first block
+    ecb_encrypt(&mut encrypted[0..8], &key); // transform first block
+
+    // Rest of the block
+    for i in (8..len).step_by(8) {
+        encrypted.xor_prev_tea_block(i); // XOR iv2
+        iv1.copy_tea_block(i, &encrypted, i); // store iv1
+        ecb_encrypt(&mut encrypted[i..i + 8], &key); // TEA ECB
+        encrypted.xor_tea_block(i, &iv1, i - 8); // XOR iv1 (from prev block)
+    }
+
+    // Done.
+    Some(encrypted)
+}
+
+/// Decrypts a byte array containing the following:
+/// * PadLen  (1 byte)
+/// * Padding (variable, 0-7byte)
+/// * Salt    (2 bytes)
+/// * Body    (? bytes)
+/// * Zero    (7 bytes)
+/// PadLen/Padding/Salt is random bytes. Minimum of 3 bytes.
+/// PadLen is taken from the last 3 bit of the first byte.
+pub fn decrypt<T: AsRef<[u8]>, K: AsRef<[u8]>>(encrypted: T, key: K) -> Option<Box<[u8]>> {
+    let encrypted = encrypted.as_ref();
+    let key = parse_key(key.as_ref())?;
+    let len = encrypted.len();
+    if (len < FIXED_PADDING_LEN) || (len % 8 != 0) {
+        return None;
+    }
+
+    let mut decrypted_buf = encrypted.to_vec();
+
+    // First block
+    ecb_decrypt(&mut decrypted_buf[0..8], &key);
+
+    // Rest of the block
+    for i in (8..len).step_by(8) {
+        decrypted_buf.xor_prev_tea_block(i); // xor iv1
+        ecb_decrypt(&mut decrypted_buf[i..i + 8], &key);
+    }
+
+    // Finalise: XOR iv2 (cipher text)
+    decrypted_buf.xor_block(8, len - 8, encrypted, 0);
+
+    let pad_size = usize::from(decrypted_buf[0] & 0b111);
+
+    // Prefixed with "pad_size", "padding", "salt"
+    let start_loc = 1 + pad_size + SALT_LEN;
+    let end_loc = len - ZERO_LEN;
+
+    if decrypted_buf[end_loc..].is_all_zeros() {
+        Some(
+            decrypted_buf[start_loc..end_loc]
+                .to_vec()
+                .into_boxed_slice(),
+        )
+    } else {
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Known good data, generated from its C++ implementation
+    const GOOD_ENCRYPTED_DATA: [u8; 24] = [
+        0x91, 0x09, 0x51, 0x62, 0xe3, 0xf5, 0xb6, 0xdc, //
+        0x6b, 0x41, 0x4b, 0x50, 0xd1, 0xa5, 0xb8, 0x4e, //
+        0xc5, 0x0d, 0x0c, 0x1b, 0x11, 0x96, 0xfd, 0x3c, //
+    ];
+
+    const ENCRYPTION_KEY: &'static str = "12345678ABCDEFGH";
+
+    const GOOD_DECRYPTED_DATA: [u8; 8] = [1u8, 2, 3, 4, 5, 6, 7, 8];
+
+    #[test]
+    fn tc_tea_basic_decryption() {
+        let result = decrypt(GOOD_ENCRYPTED_DATA, ENCRYPTION_KEY).unwrap();
+        assert_eq!(result, GOOD_DECRYPTED_DATA.into());
+    }
+
+    #[test]
+    fn tc_tea_decryption_reject_non_zero_byte() {
+        let mut bad_data = GOOD_ENCRYPTED_DATA.clone();
+        bad_data[23] ^= 0xff; // last byte
+        assert!(decrypt(bad_data, ENCRYPTION_KEY).is_none());
+    }
+
+    #[test]
+    fn tc_tea_basic_encryption() {
+        let encrypted = encrypt(GOOD_DECRYPTED_DATA, ENCRYPTION_KEY).unwrap();
+        assert_eq!(encrypted.len(), 24);
+
+        // Since encryption utilises random numbers, we are just going to
+        let decrypted = decrypt(encrypted, ENCRYPTION_KEY).unwrap();
+        assert_eq!(decrypted, GOOD_DECRYPTED_DATA.into());
+    }
+
+    #[test]
+    fn test_calc_encrypted_size() {
+        assert_eq!(calc_encrypted_size(0), 16);
+        assert_eq!(calc_encrypted_size(1), 16);
+        assert_eq!(calc_encrypted_size(6), 16);
+
+        assert_eq!(calc_encrypted_size(7), 24);
+        assert_eq!(calc_encrypted_size(14), 24);
+        assert_eq!(calc_encrypted_size(15), 32);
+    }
+}

src/tc_tea_internal.rs

@@ -0,0 +1,63 @@
+use super::stream_ext::StreamExt;
+
+const ROUNDS: u32 = 16;
+const DELTA: u32 = 0x9e3779b9;
+
+#[inline]
+pub fn parse_key(key: &[u8]) -> Option<[u32; 4]> {
+    if key.len() < 16 {
+        return None;
+    }
+
+    let mut k = [0u32; 4];
+    for (i, k) in k.iter_mut().enumerate() {
+        *k = key.read_u32_be(i * 4);
+    }
+    return Some(k);
+}
+
+#[inline]
+/// Perform a single round of encrypting/decrypting wrapping arithmetics
+fn tc_tea_single_round_arithmetic(value: u32, sum: u32, key1: u32, key2: u32) -> u32 {
+    // ((y << 4) + k[2]) ^ (y + sum) ^ ((y >> 5) + k[3]);
+
+    value.wrapping_shl(4).wrapping_add(key1)
+        ^ sum.wrapping_add(value)
+        ^ value.wrapping_shr(5).wrapping_add(key2)
+}
+
+#[inline]
+/// Perform a single operation of TEA ECB decryption.
+pub fn ecb_decrypt(block: &mut [u8], k: &[u32; 4]) {
+    let mut y = block.read_u32_be(0);
+    let mut z = block.read_u32_be(4);
+    let mut sum = DELTA.wrapping_mul(ROUNDS);
+
+    for _ in 0..ROUNDS {
+        z = z.wrapping_sub(tc_tea_single_round_arithmetic(y, sum, k[2], k[3]));
+        y = y.wrapping_sub(tc_tea_single_round_arithmetic(z, sum, k[0], k[1]));
+
+        sum = sum.wrapping_sub(DELTA);
+    }
+
+    block.write_u32_be(0, y);
+    block.write_u32_be(4, z);
+}
+
+#[inline]
+/// Perform a single operation of TEA ECB encryption.
+pub fn ecb_encrypt(block: &mut [u8], k: &[u32; 4]) {
+    let mut y = block.read_u32_be(0);
+    let mut z = block.read_u32_be(4);
+    let mut sum = 0_u32;
+
+    for _ in 0..ROUNDS {
+        sum = sum.wrapping_add(DELTA);
+
+        y = y.wrapping_add(tc_tea_single_round_arithmetic(z, sum, k[0], k[1]));
+        z = z.wrapping_add(tc_tea_single_round_arithmetic(y, sum, k[2], k[3]));
+    }
+
+    block.write_u32_be(0, y);
+    block.write_u32_be(4, z);
+}