oxirush-security 0.1.0

//! ZUC stream cipher (3GPP TS 35.221 / TS 35.222)
//!
//! A word-oriented stream cipher producing 32-bit keystream words.
//! Uses a 16-stage LFSR over GF(2^31-1), bit reorganization, and a nonlinear function.

// ── S-boxes ────────────────────────────────────────────────────────────────────

const S0: [u8; 256] = [
    0x3E, 0x72, 0x5B, 0x47, 0xCA, 0xE0, 0x00, 0x33, 0x04, 0xD1, 0x54, 0x98, 0x09, 0xB9, 0x6D, 0xCB,
    0x7B, 0x1B, 0xF9, 0x32, 0xAF, 0x9D, 0x6A, 0xA5, 0xB8, 0x2D, 0xFC, 0x1D, 0x08, 0x53, 0x03, 0x90,
    0x4D, 0x4E, 0x84, 0x99, 0xE4, 0xCE, 0xD9, 0x91, 0xDD, 0xB6, 0x85, 0x48, 0x8B, 0x29, 0x6E, 0xAC,
    0xCD, 0xC1, 0xF8, 0x1E, 0x73, 0x43, 0x69, 0xC6, 0xB5, 0xBD, 0xFD, 0x39, 0x63, 0x20, 0xD4, 0x38,
    0x76, 0x7D, 0xB2, 0xA7, 0xCF, 0xED, 0x57, 0xC5, 0xF3, 0x2C, 0xBB, 0x14, 0x21, 0x06, 0x55, 0x9B,
    0xE3, 0xEF, 0x5E, 0x31, 0x4F, 0x7F, 0x5A, 0xA4, 0x0D, 0x82, 0x51, 0x49, 0x5F, 0xBA, 0x58, 0x1C,
    0x4A, 0x16, 0xD5, 0x17, 0xA8, 0x92, 0x24, 0x1F, 0x8C, 0xFF, 0xD8, 0xAE, 0x2E, 0x01, 0xD3, 0xAD,
    0x3B, 0x4B, 0xDA, 0x46, 0xEB, 0xC9, 0xDE, 0x9A, 0x8F, 0x87, 0xD7, 0x3A, 0x80, 0x6F, 0x2F, 0xC8,
    0xB1, 0xB4, 0x37, 0xF7, 0x0A, 0x22, 0x13, 0x28, 0x7C, 0xCC, 0x3C, 0x89, 0xC7, 0xC3, 0x96, 0x56,
    0x07, 0xBF, 0x7E, 0xF0, 0x0B, 0x2B, 0x97, 0x52, 0x35, 0x41, 0x79, 0x61, 0xA6, 0x4C, 0x10, 0xFE,
    0xBC, 0x26, 0x95, 0x88, 0x8A, 0xB0, 0xA3, 0xFB, 0xC0, 0x18, 0x94, 0xF2, 0xE1, 0xE5, 0xE9, 0x5D,
    0xD0, 0xDC, 0x11, 0x66, 0x64, 0x5C, 0xEC, 0x59, 0x42, 0x75, 0x12, 0xF5, 0x74, 0x9C, 0xAA, 0x23,
    0x0E, 0x86, 0xAB, 0xBE, 0x2A, 0x02, 0xE7, 0x67, 0xE6, 0x44, 0xA2, 0x6C, 0xC2, 0x93, 0x9F, 0xF1,
    0xF6, 0xFA, 0x36, 0xD2, 0x50, 0x68, 0x9E, 0x62, 0x71, 0x15, 0x3D, 0xD6, 0x40, 0xC4, 0xE2, 0x0F,
    0x8E, 0x83, 0x77, 0x6B, 0x25, 0x05, 0x3F, 0x0C, 0x30, 0xEA, 0x70, 0xB7, 0xA1, 0xE8, 0xA9, 0x65,
    0x8D, 0x27, 0x1A, 0xDB, 0x81, 0xB3, 0xA0, 0xF4, 0x45, 0x7A, 0x19, 0xDF, 0xEE, 0x78, 0x34, 0x60,
];

const S1: [u8; 256] = [
    0x55, 0xC2, 0x63, 0x71, 0x3B, 0xC8, 0x47, 0x86, 0x9F, 0x3C, 0xDA, 0x5B, 0x29, 0xAA, 0xFD, 0x77,
    0x8C, 0xC5, 0x94, 0x0C, 0xA6, 0x1A, 0x13, 0x00, 0xE3, 0xA8, 0x16, 0x72, 0x40, 0xF9, 0xF8, 0x42,
    0x44, 0x26, 0x68, 0x96, 0x81, 0xD9, 0x45, 0x3E, 0x10, 0x76, 0xC6, 0xA7, 0x8B, 0x39, 0x43, 0xE1,
    0x3A, 0xB5, 0x56, 0x2A, 0xC0, 0x6D, 0xB3, 0x05, 0x22, 0x66, 0xBF, 0xDC, 0x0B, 0xFA, 0x62, 0x48,
    0xDD, 0x20, 0x11, 0x06, 0x36, 0xC9, 0xC1, 0xCF, 0xF6, 0x27, 0x52, 0xBB, 0x69, 0xF5, 0xD4, 0x87,
    0x7F, 0x84, 0x4C, 0xD2, 0x9C, 0x57, 0xA4, 0xBC, 0x4F, 0x9A, 0xDF, 0xFE, 0xD6, 0x8D, 0x7A, 0xEB,
    0x2B, 0x53, 0xD8, 0x5C, 0xA1, 0x14, 0x17, 0xFB, 0x23, 0xD5, 0x7D, 0x30, 0x67, 0x73, 0x08, 0x09,
    0xEE, 0xB7, 0x70, 0x3F, 0x61, 0xB2, 0x19, 0x8E, 0x4E, 0xE5, 0x4B, 0x93, 0x8F, 0x5D, 0xDB, 0xA9,
    0xAD, 0xF1, 0xAE, 0x2E, 0xCB, 0x0D, 0xFC, 0xF4, 0x2D, 0x46, 0x6E, 0x1D, 0x97, 0xE8, 0xD1, 0xE9,
    0x4D, 0x37, 0xA5, 0x75, 0x5E, 0x83, 0x9E, 0xAB, 0x82, 0x9D, 0xB9, 0x1C, 0xE0, 0xCD, 0x49, 0x89,
    0x01, 0xB6, 0xBD, 0x58, 0x24, 0xA2, 0x5F, 0x38, 0x78, 0x99, 0x15, 0x90, 0x50, 0xB8, 0x95, 0xE4,
    0xD0, 0x91, 0xC7, 0xCE, 0xED, 0x0F, 0xB4, 0x6F, 0xA0, 0xCC, 0xF0, 0x02, 0x4A, 0x79, 0xC3, 0xDE,
    0xA3, 0xEF, 0xEA, 0x51, 0xE6, 0x6B, 0x18, 0xEC, 0x1B, 0x2C, 0x80, 0xF7, 0x74, 0xE7, 0xFF, 0x21,
    0x5A, 0x6A, 0x54, 0x1E, 0x41, 0x31, 0x92, 0x35, 0xC4, 0x33, 0x07, 0x0A, 0xBA, 0x7E, 0x0E, 0x34,
    0x88, 0xB1, 0x98, 0x7C, 0xF3, 0x3D, 0x60, 0x6C, 0x7B, 0xCA, 0xD3, 0x1F, 0x32, 0x65, 0x04, 0x28,
    0x64, 0xBE, 0x85, 0x9B, 0x2F, 0x59, 0x8A, 0xD7, 0xB0, 0x25, 0xAC, 0xAF, 0x12, 0x03, 0xE2, 0xF2,
];

// ── Constants ──────────────────────────────────────────────────────────────────

/// 15-bit constants d[i] for LFSR initialization
const D: [u16; 16] = [
    0x44D7, 0x26BC, 0x626B, 0x135E, 0x5789, 0x35E2, 0x7135, 0x09AF, 0x4D78, 0x2F13, 0x6BC4, 0x1AF1,
    0x5E26, 0x3C4D, 0x789A, 0x47AC,
];

const P: u32 = 0x7FFFFFFF; // 2^31 - 1

// ── Modular arithmetic mod 2^31-1 ──────────────────────────────────────────────

/// Reduce mod 2^31-1, result in [1, 2^31-1] (0 maps to P)
#[inline]
fn mod31(a: u32) -> u32 {
    let mut r = (a & P) + (a >> 31);
    if r >= P {
        r -= P;
    }
    if r == 0 { P } else { r }
}

/// Multiply by 2^n mod (2^31-1)
#[inline]
fn rot31(a: u32, n: u32) -> u32 {
    ((a << n) | (a >> (31 - n))) & P
}

// ── Linear transforms ──────────────────────────────────────────────────────────

#[inline]
fn l1(x: u32) -> u32 {
    x ^ x.rotate_left(2) ^ x.rotate_left(10) ^ x.rotate_left(18) ^ x.rotate_left(24)
}

#[inline]
fn l2(x: u32) -> u32 {
    x ^ x.rotate_left(8) ^ x.rotate_left(14) ^ x.rotate_left(22) ^ x.rotate_left(30)
}

/// Apply S-boxes to a 32-bit word: S0(x0) || S1(x1) || S0(x2) || S1(x3)
#[inline]
fn sbox(x: u32) -> u32 {
    let b = x.to_be_bytes();
    u32::from_be_bytes([
        S0[b[0] as usize],
        S1[b[1] as usize],
        S0[b[2] as usize],
        S1[b[3] as usize],
    ])
}

// ── ZUC state ──────────────────────────────────────────────────────────────────

#[derive(zeroize::Zeroize, zeroize::ZeroizeOnDrop)]
pub struct Zuc {
    s: [u32; 16], // LFSR (31-bit stages)
    r1: u32,
    r2: u32,
}

impl Zuc {
    /// Initialize ZUC with 128-bit key and 128-bit IV.
    pub fn new(key: &[u8; 16], iv: &[u8; 16]) -> Self {
        let mut z = Zuc {
            s: [0u32; 16],
            r1: 0,
            r2: 0,
        };

        // Load LFSR: s[i] = k[i] || d[i] || iv[i] (31 bits: 8+15+8)
        for i in 0..16 {
            z.s[i] = ((key[i] as u32) << 23) | ((D[i] as u32) << 8) | (iv[i] as u32);
        }

        // 32 initialization clocks
        for _ in 0..32 {
            let (x0, x1, x2, x3) = z.bit_reorg();
            let w = z.f(x0, x1, x2, x3);
            z.lfsr_init(w >> 1);
        }

        z
    }

    /// Generate `n` keystream words.
    pub fn generate(&mut self, n: usize) -> Vec<u32> {
        // Discard first output
        let (x0, x1, x2, x3) = self.bit_reorg();
        let _ = self.f(x0, x1, x2, x3);
        self.lfsr_keystream();

        let mut ks = Vec::with_capacity(n);
        for _ in 0..n {
            let (x0, x1, x2, x3) = self.bit_reorg();
            let w = self.f(x0, x1, x2, x3);
            ks.push(w ^ x3);
            self.lfsr_keystream();
        }
        ks
    }

    /// Bit Reorganization: extract X0..X3 from LFSR stages.
    #[inline]
    fn bit_reorg(&self) -> (u32, u32, u32, u32) {
        let x0 = ((self.s[15] & 0x7FFF8000) << 1) | (self.s[14] & 0xFFFF);
        let x1 = ((self.s[11] & 0xFFFF) << 16) | (self.s[9] >> 15);
        let x2 = ((self.s[7] & 0xFFFF) << 16) | (self.s[5] >> 15);
        let x3 = ((self.s[2] & 0xFFFF) << 16) | (self.s[0] >> 15);
        (x0, x1, x2, x3)
    }

    /// Nonlinear function F.
    fn f(&mut self, x0: u32, x1: u32, x2: u32, x3: u32) -> u32 {
        let w = (x0 ^ self.r1).wrapping_add(self.r2);
        let w1 = self.r1.wrapping_add(x1);
        let w2 = self.r2 ^ x2;

        // Swap halves
        let u = (w1 << 16) | (w2 >> 16);
        let v = (w2 << 16) | (w1 >> 16);

        self.r1 = sbox(l1(u));
        self.r2 = sbox(l2(v));

        let _ = x3; // x3 used by caller for keystream output
        w
    }

    /// LFSR clock during initialization (feedback includes W).
    fn lfsr_init(&mut self, w: u32) {
        let mut f = self.s[0];
        f = mod31(f.wrapping_add(rot31(self.s[0], 8)));
        f = mod31(f.wrapping_add(rot31(self.s[4], 20)));
        f = mod31(f.wrapping_add(rot31(self.s[10], 21)));
        f = mod31(f.wrapping_add(rot31(self.s[13], 17)));
        f = mod31(f.wrapping_add(rot31(self.s[15], 15)));
        f = mod31(f.wrapping_add(w & P));

        for i in 0..15 {
            self.s[i] = self.s[i + 1];
        }
        self.s[15] = if f == 0 { P } else { f };
    }

    /// LFSR clock during keystream generation.
    fn lfsr_keystream(&mut self) {
        let mut f = self.s[0];
        f = mod31(f.wrapping_add(rot31(self.s[0], 8)));
        f = mod31(f.wrapping_add(rot31(self.s[4], 20)));
        f = mod31(f.wrapping_add(rot31(self.s[10], 21)));
        f = mod31(f.wrapping_add(rot31(self.s[13], 17)));
        f = mod31(f.wrapping_add(rot31(self.s[15], 15)));

        for i in 0..15 {
            self.s[i] = self.s[i + 1];
        }
        self.s[15] = if f == 0 { P } else { f };
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_zuc_test_vector_1() {
        // ZUC 1.6 (TS 35.221): all-zero key and IV
        // Note: ZUC 1.4 produced 0x27BEAD9D; ZUC 1.6 produces 0x27BEDE74
        let key = [0u8; 16];
        let iv = [0u8; 16];
        let mut z = Zuc::new(&key, &iv);
        let ks = z.generate(2);
        assert_eq!(ks[0], 0x27BE_DE74);
    }

    #[test]
    fn test_zuc_test_vector_2() {
        // 3GPP TS 35.221 Test Set 2: all-FF key and IV
        let key = [0xFFu8; 16];
        let iv = [0xFFu8; 16];
        let mut z = Zuc::new(&key, &iv);
        let ks = z.generate(2);
        assert_eq!(ks[0], 0x0657_CFA0);
        assert_eq!(ks[1], 0x7096_398B);
    }

    #[test]
    fn test_zuc_test_vector_3() {
        // 3GPP TS 35.221 Test Set 3
        let key: [u8; 16] = [
            0x3D, 0x4C, 0x4B, 0xE9, 0x6A, 0x82, 0xFD, 0xAE, 0xB5, 0x8F, 0x64, 0x1D, 0xB1, 0x7B,
            0x45, 0x5B,
        ];
        let iv: [u8; 16] = [
            0x84, 0x31, 0x9A, 0xA8, 0xDE, 0x69, 0x15, 0xCA, 0x1F, 0x6B, 0xDA, 0x6B, 0xFB, 0xD8,
            0xC7, 0x66,
        ];
        let mut z = Zuc::new(&key, &iv);
        let ks = z.generate(2);
        assert_eq!(ks[0], 0x14F1_C272);
        assert_eq!(ks[1], 0x3279_C419);
    }
}