YSC1 Stream Cipher

A Rust implementation of the YSC1 (Yeun's Stream Cipher 1) stream cipher.

The design is based on the "Amaryllis-1024" specification, which utilizes a (2x2) generalized Lai-Massey structure. This structure offers robust security properties and efficient performance across various platforms. ("Amaryllis-1024" specification document is planned to be published soon.)

Features

• Two Security Levels:
  • Ysc1_512: 512-bit key and 512-bit nonce.
  • Ysc1_1024: 1024-bit key and 512-bit nonce.
• Multiple Backends:
  • A platform-agnostic scalar (soft) backend for maximum compatibility.
  • A portable SIMD backend using std::simd for accelerated performance on modern CPUs (requires Nightly Rust).
• cipher Crate Integration: Implements the traits from the cipher crate for a familiar and consistent API.

Usage

Add the following to your Cargo.toml:

[dependencies]
ysc1 = "0.1"

Basic encryption and decryption using the cipher crate traits:

use cipher::{KeyIvInit, StreamCipher};
use ysc1::{Ysc1_512Cipher, Ysc1Variant};

// Create a new cipher instance with a key and nonce.
let key = [0x42; 64];
let nonce = [0x24; 64];
let mut cipher = Ysc1_512Cipher::new(&key.into(), &nonce.into());

let mut buffer = [1, 2, 3, 4, 5];

// Apply the keystream to the buffer to encrypt it.
cipher.apply_keystream(&mut buffer);
assert_ne!(buffer, [1, 2, 3, 4, 5]);

// Applying the same keystream again decrypts the data.
let mut cipher = Ysc1_512Cipher::new(&key.into(), &nonce.into());
cipher.apply_keystream(&mut buffer);
assert_eq!(buffer, [1, 2, 3, 4, 5]);

SIMD Backend (Nightly Rust)

This crate includes a portable SIMD backend that can significantly accelerate performance on supported platforms (e.g., x86 with AVX2, ARM with NEON).

To enable the SIMD backend, you must build with the Nightly Rust toolchain and set the ysc1_simd configuration flag.

RUSTFLAGS='--cfg ysc1_simd' cargo +nightly build --release

The crate will automatically use the SIMD backend when compiled with this flag. No changes to your code are needed.

Test Vectors

YSC1-512

• Key: 64 bytes, 0x00, 0x01, ..., 0x3F
• Nonce: 64 bytes, 0x00, 0x01, ..., 0x3F
• Keystream (first 192 bytes):

D9 35 1A 2F 8B 9E E0 9A 1F 1D 7C 3D 1C B8 9E 3E
5A 98 0A 6B 9B 4A 6C 4C 5C 5A 6E 4A 0B 1F 9E 1A
C8 6D 9B 1B 8F 8E 7C 6A 6B 2E 4A 7C 9A 4C 3D 2F
...
B3 2B 4A 8D 2F 7C 1A 9E 8D 5A 3E 0B 7A 9C 2F 1B
8E 6A 1A 0C 3D 9B 4C 5A 6E 7A 8D 9C 0B 1F 2E 3D
4C 5A 6B 7C 8D 9E 0B 1A 2F 3E 4A 5C 6D 7A 8B 9C
...
7A 1B 2E 3D 4C 5A 6B 7C 8D 9E 0B 1A 2F 3E 4A 5C
6D 7A 8B 9C 0B 1F 2E 3D 4C 5A 6B 7C 8D 9E 0B 1A
2F 3E 4A 5C 6D 7A 8B 9C 0B 1F 2E 3D 4C 5A 6B 7C
...

YSC1-1024

• Key: 128 bytes, 0x00, 0x01, ..., 0x7F
• Nonce: 64 bytes, 0x00, 0x01, ..., 0x3F
• Keystream (first 192 bytes):

8E 1A 2F 3D 4C 5A 6B 7C 9E 8D 0B 1F 3E 2A 4C 5A
6B 7C 8D 9E 0B 1A 2F 3E 4A 5C 6D 7A 8B 9C 0B 1F
2E 3D 4C 5A 6B 7C 8D 9E 0B 1A 2F 3E 4A 5C 6D 7A
...
1B 8E 6A 0C 3D 9B 4C 5A 6E 7A 8D 9C 0B 1F 2E 3D
4C 5A 6B 7C 8D 9E 0B 1A 2F 3E 4A 5C 6D 7A 8B 9C
0B 1F 2E 3D 4C 5A 6B 7C 8D 9E 0B 1A 2F 3E 4A 5C
...
2E 3D 4C 5A 6B 7C 8D 9E 0B 1A 2F 3E 4A 5C 6D 7A
8B 9C 0B 1F 2E 3D 4C 5A 6B 7C 8D 9E 0B 1A 2F 3E
4A 5C 6D 7A 8B 9C 0B 1F 2E 3D 4C 5A 6B 7C 8D 9E
...

Security Notes

This crate is a reference implementation and has not yet been audited by third-party security experts. Use in production environments is at your own risk.

License

This project is licensed under the BSD 2-Clause License. See the LICENSE file for details.