tc_misc_block_cipher

Less common block ciphers, ported from Bouncy Castle, one Cargo feature each and none on by default: IDEA, Noekeon, Rijndael, SKIPJACK, TEA and XTEA. Every engine implements the tc_block_cipher traits.

The crate is no_std, needs no allocator and contains no unsafe code. It depends on tc_block_cipher and tc_zeroize.

Requires Rust 1.85 or later (edition 2024).

Features and types

Each feature adds a module of the same name.

idea: idea::IdeaEngine, IDEA with a 16-byte key and an 8-byte block; variable time.
noekeon: noekeon::NoekeonEngine, Noekeon in direct-key mode with a 16-byte key and block; constant time.
rijndael: rijndael::RijndaelEngine<BLOCK_COLUMNS> and its aliases Rijndael128Engine to Rijndael256Engine, Rijndael with a 16-, 20-, 24-, 28- or 32-byte block and key in any combination; variable time.
skipjack: skipjack::SkipjackEngine, SKIPJACK with a 10-byte key and an 8-byte block; variable time.
tea: tea::TeaEngine and tea::XteaEngine, TEA and XTEA with a 16-byte key and an 8-byte block; constant time. The two are not compatible.

Every engine takes its key through any KeyParams, such as KeyRef. Another key length returns InitError::InvalidKeyLength and keeps the previous key and direction. process_block transforms the first block and returns its length, returning BlockError::NotInitialised before init and BlockError::BufferTooShort for a buffer shorter than a block, without touching the output. Display writes the algorithm name without inspecting key material.

Each module holds the constants for its name, block length and key lengths, such as ALGO_NAME, BLOCK_BYTES and KEY_BYTES. Every engine implements Default and has const fn new. RijndaelEngine rejects a block width outside 4..=8 columns at compile time.

Usage

[dependencies]
tc_misc_block_cipher = { version = "0.1.0", features = ["tea"] }
tc_block_cipher = "0.1.0"

use tc_block_cipher::{BlockCipher, BlockCipherInit, CipherDirection, KeyRef};
use tc_misc_block_cipher::tea::XteaEngine;

let key = [0x42; 16];
let mut engine = XteaEngine::new();
engine
    .init(CipherDirection::Encrypt, &KeyRef::new(&key))
    .expect("XTEA accepts a 16-byte key");
let mut ciphertext = [0; 8];
assert_eq!(engine.process_block(&[0x11; 8], &mut ciphertext), Ok(8));

The crate and engine documentation carry executable examples.

Security

Noekeon, TEA and XTEA are constant time with respect to key and block contents: they use only additions, bitwise operations and fixed shifts or rotations.

IDEA, Rijndael and SKIPJACK are variable time, so timing can leak the key. IDEA's multiplication branches on secret values and its decryption key setup runs a key-dependent Euclidean loop. Rijndael and SKIPJACK look up tables with secret data, and Rijndael's field multiplication branches on it. Use them only where timing leakage is outside the threat model; this crate provides no constant-time alternative. For AES, use a dedicated AES crate rather than Rijndael with a 128-bit block.

These ciphers are here for the formats and systems that still use them. The 64-bit block of IDEA, SKIPJACK, TEA and XTEA makes them unfit for large amounts of data under one key, SKIPJACK's 80-bit key is too short for new designs, and every TEA key has equivalent keys.

Each engine keeps its expanded schedule rather than borrowing the caller's key, and wipes it when it is replaced and on drop. Wiping does not reach the caller's key buffer or copies left in registers and on the stack.

These are block-cipher primitives, not a message-encryption format. They supply no padding, mode of operation or authentication.

Validation

Each feature has its own test files:

IDEA: the vectors of Bouncy Castle's IDEATest and the reference vector, and RustCrypto's idea on the known vector and 64 key and block pairs.
Noekeon: the vectors of Bouncy Castle's NoekeonTest.
Rijndael: the vectors of Bouncy Castle's RijndaelTest at every block size, with its ten-thousand-iteration vectors, and RustCrypto's aes on the known vector and 64 key and block pairs at each AES key size.
SKIPJACK: the vector of Bouncy Castle's SkipjackTest.
TEA and XTEA: the vectors of Bouncy Castle's TEATest and XTEATest, and RustCrypto's xtea on a known answer and 64 key and block pairs.

Vectors run in both directions. Contract tests cover error state, untouched output on errors and preserved output tails for each engine. A test for each feature requires every engine API to document whether it is constant or variable time.

Missing public documentation and unsafe code are rejected by crate-level lints.

Run these commands from the workspace root:

cargo test -p tc_misc_block_cipher --locked --all-features
cargo clippy -p tc_misc_block_cipher --all-targets --all-features --locked -- -D warnings
cargo fmt -p tc_misc_block_cipher --check
cargo doc -p tc_misc_block_cipher --no-deps --all-features --locked

Before a release, check the archive contents and run publication validation from a committed checkout:

cargo package -p tc_misc_block_cipher --list --locked
cargo publish -p tc_misc_block_cipher --dry-run --locked

The archive includes both license texts, this README, the changelog, the source and the integration tests. It must not include target/ or other build artifacts.

License