libfreemkv 0.10.3

//! CSS drive authentication — SCSI handshake to unlock scrambled sector reads.
//!
//! Pure SCSI (REPORT KEY / SEND KEY). Works on all platforms via ScsiTransport.
//!
//! The CSS auth uses a challenge-response with a 6-round substitution-permutation
//! cipher (CSSCryptKey). This is DIFFERENT from the content descrambling cipher.
//!
//! Protocol:
//!   1. Allocate AGID
//!   2. Host sends challenge, drive returns Key1
//!   3. Host brute-forces variant (0-31) by checking which produces Key1
//!   4. Drive sends challenge, host computes Key2 using found variant
//!   5. Host sends Key2, drive verifies — authentication complete
//!
//! Based on Stevenson 1999 analysis and libdvdcss CSSAuth()/CSSCryptKey().

use crate::drive::Drive;
use crate::error::{Error, Result};

// ── Tables from csstables.h (libdvdcss) ────────────────────────────────────

const CRYPT_TAB0: [u8; 256] = [
    0xB7, 0xF4, 0x82, 0x57, 0xDA, 0x4D, 0xDB, 0xE2, 0x2F, 0x52, 0x1A, 0xA8, 0x68, 0x5A, 0x8A, 0xFF,
    0xFB, 0x0E, 0x6D, 0x35, 0xF7, 0x5C, 0x76, 0x12, 0xCE, 0x25, 0x79, 0x29, 0x39, 0x62, 0x08, 0x24,
    0xA5, 0x85, 0x7B, 0x56, 0x01, 0x23, 0x68, 0xCF, 0x0A, 0xE2, 0x5A, 0xED, 0x3D, 0x59, 0xB0, 0xA9,
    0xB0, 0x2C, 0xF2, 0xB8, 0xEF, 0x32, 0xA9, 0x40, 0x80, 0x71, 0xAF, 0x1E, 0xDE, 0x8F, 0x58, 0x88,
    0xB8, 0x3A, 0xD0, 0xFC, 0xC4, 0x1E, 0xB5, 0xA0, 0xBB, 0x3B, 0x0F, 0x01, 0x7E, 0x1F, 0x9F, 0xD9,
    0xAA, 0xB8, 0x3D, 0x9D, 0x74, 0x1E, 0x25, 0xDB, 0x37, 0x56, 0x8F, 0x16, 0xBA, 0x49, 0x2B, 0xAC,
    0xD0, 0xBD, 0x95, 0x20, 0xBE, 0x7A, 0x28, 0xD0, 0x51, 0x64, 0x63, 0x1C, 0x7F, 0x66, 0x10, 0xBB,
    0xC4, 0x56, 0x1A, 0x04, 0x6E, 0x0A, 0xEC, 0x9C, 0xD6, 0xE8, 0x9A, 0x7A, 0xCF, 0x8C, 0xDB, 0xB1,
    0xEF, 0x71, 0xDE, 0x31, 0xFF, 0x54, 0x3E, 0x5E, 0x07, 0x69, 0x96, 0xB0, 0xCF, 0xDD, 0x9E, 0x47,
    0xC7, 0x96, 0x8F, 0xE4, 0x2B, 0x59, 0xC6, 0xEE, 0xB9, 0x86, 0x9A, 0x64, 0x84, 0x72, 0xE2, 0x5B,
    0xA2, 0x96, 0x58, 0x99, 0x50, 0x03, 0xF5, 0x38, 0x4D, 0x02, 0x7D, 0xE7, 0x7D, 0x75, 0xA7, 0xB8,
    0x67, 0x87, 0x84, 0x3F, 0x1D, 0x11, 0xE5, 0xFC, 0x1E, 0xD3, 0x83, 0x16, 0xA5, 0x29, 0xF6, 0xC7,
    0x15, 0x61, 0x29, 0x1A, 0x43, 0x4F, 0x9B, 0xAF, 0xC5, 0x87, 0x34, 0x6C, 0x0F, 0x3B, 0xA8, 0x1D,
    0x45, 0x58, 0x25, 0xDC, 0xA8, 0xA3, 0x3B, 0xD1, 0x79, 0x1B, 0x48, 0xF2, 0xE9, 0x93, 0x1F, 0xFC,
    0xDB, 0x2A, 0x90, 0xA9, 0x8A, 0x3D, 0x39, 0x18, 0xA3, 0x8E, 0x58, 0x6C, 0xE0, 0x12, 0xBB, 0x25,
    0xCD, 0x71, 0x22, 0xA2, 0x64, 0xC6, 0xE7, 0xFB, 0xAD, 0x94, 0x77, 0x04, 0x9A, 0x39, 0xCF, 0x7C,
];

const CRYPT_TAB1: [u8; 256] = [
    0x8C, 0x47, 0xB0, 0xE1, 0xEB, 0xFC, 0xEB, 0x56, 0x10, 0xE5, 0x2C, 0x1A, 0x5D, 0xEF, 0xBE, 0x4F,
    0x08, 0x75, 0x97, 0x4B, 0x0E, 0x25, 0x8E, 0x6E, 0x39, 0x5A, 0x87, 0x53, 0xC4, 0x1F, 0xF4, 0x5C,
    0x4E, 0xE6, 0x99, 0x30, 0xE0, 0x42, 0x88, 0xAB, 0xE5, 0x85, 0xBC, 0x8F, 0xD8, 0x3C, 0x54, 0xC9,
    0x53, 0x47, 0x18, 0xD6, 0x06, 0x5B, 0x41, 0x2C, 0x67, 0x1E, 0x41, 0x74, 0x33, 0xE2, 0xB4, 0xE0,
    0x23, 0x29, 0x42, 0xEA, 0x55, 0x0F, 0x25, 0xB4, 0x24, 0x2C, 0x99, 0x13, 0xEB, 0x0A, 0x0B, 0xC9,
    0xF9, 0x63, 0x67, 0x43, 0x2D, 0xC7, 0x7D, 0x07, 0x60, 0x89, 0xD1, 0xCC, 0xE7, 0x94, 0x77, 0x74,
    0x9B, 0x7E, 0xD7, 0xE6, 0xFF, 0xBB, 0x68, 0x14, 0x1E, 0xA3, 0x25, 0xDE, 0x3A, 0xA3, 0x54, 0x7B,
    0x87, 0x9D, 0x50, 0xCA, 0x27, 0xC3, 0xA4, 0x50, 0x91, 0x27, 0xD4, 0xB0, 0x82, 0x41, 0x97, 0x79,
    0x94, 0x82, 0xAC, 0xC7, 0x8E, 0xA5, 0x4E, 0xAA, 0x78, 0x9E, 0xE0, 0x42, 0xBA, 0x28, 0xEA, 0xB7,
    0x74, 0xAD, 0x35, 0xDA, 0x92, 0x60, 0x7E, 0xD2, 0x0E, 0xB9, 0x24, 0x5E, 0x39, 0x4F, 0x5E, 0x63,
    0x09, 0xB5, 0xFA, 0xBF, 0xF1, 0x22, 0x55, 0x1C, 0xE2, 0x25, 0xDB, 0xC5, 0xD8, 0x50, 0x03, 0x98,
    0xC4, 0xAC, 0x2E, 0x11, 0xB4, 0x38, 0x4D, 0xD0, 0xB9, 0xFC, 0x2D, 0x3C, 0x08, 0x04, 0x5A, 0xEF,
    0xCE, 0x32, 0xFB, 0x4C, 0x92, 0x1E, 0x4B, 0xFB, 0x1A, 0xD0, 0xE2, 0x3E, 0xDA, 0x6E, 0x7C, 0x4D,
    0x56, 0xC3, 0x3F, 0x42, 0xB1, 0x3A, 0x23, 0x4D, 0x6E, 0x84, 0x56, 0x68, 0xF4, 0x0E, 0x03, 0x64,
    0xD0, 0xA9, 0x92, 0x2F, 0x8B, 0xBC, 0x39, 0x9C, 0xAC, 0x09, 0x5E, 0xEE, 0xE5, 0x97, 0xBF, 0xA5,
    0xCE, 0xFA, 0x28, 0x2C, 0x6D, 0x4F, 0xEF, 0x77, 0xAA, 0x1B, 0x79, 0x8E, 0x97, 0xB4, 0xC3, 0xF4,
];

const CRYPT_TAB2: [u8; 256] = [
    0xB7, 0x75, 0x81, 0xD5, 0xDC, 0xCA, 0xDE, 0x66, 0x23, 0xDF, 0x15, 0x26, 0x62, 0xD1, 0x83, 0x77,
    0xE3, 0x97, 0x76, 0xAF, 0xE9, 0xC3, 0x6B, 0x8E, 0xDA, 0xB0, 0x6E, 0xBF, 0x2B, 0xF1, 0x19, 0xB4,
    0x95, 0x34, 0x48, 0xE4, 0x37, 0x94, 0x5D, 0x7B, 0x36, 0x5F, 0x65, 0x53, 0x07, 0xE2, 0x89, 0x11,
    0x98, 0x85, 0xD9, 0x12, 0xC1, 0x9D, 0x84, 0xEC, 0xA4, 0xD4, 0x88, 0xB8, 0xFC, 0x2C, 0x79, 0x28,
    0xD8, 0xDB, 0xB3, 0x1E, 0xA2, 0xF9, 0xD0, 0x44, 0xD7, 0xD6, 0x60, 0xEF, 0x14, 0xF4, 0xF6, 0x31,
    0xD2, 0x41, 0x46, 0x67, 0x0A, 0xE1, 0x58, 0x27, 0x43, 0xA3, 0xF8, 0xE0, 0xC8, 0xBA, 0x5A, 0x5C,
    0x80, 0x6C, 0xC6, 0xF2, 0xE8, 0xAD, 0x7D, 0x04, 0x0D, 0xB9, 0x3C, 0xC2, 0x25, 0xBD, 0x49, 0x63,
    0x8C, 0x9F, 0x51, 0xCE, 0x20, 0xC5, 0xA1, 0x50, 0x92, 0x2D, 0xDD, 0xBC, 0x8D, 0x4F, 0x9A, 0x71,
    0x2F, 0x30, 0x1D, 0x73, 0x39, 0x13, 0xFB, 0x1A, 0xCB, 0x24, 0x59, 0xFE, 0x05, 0x96, 0x57, 0x0F,
    0x1F, 0xCF, 0x54, 0xBE, 0xF5, 0x06, 0x1B, 0xB2, 0x6D, 0xD3, 0x4D, 0x32, 0x56, 0x21, 0x33, 0x0B,
    0x52, 0xE7, 0xAB, 0xEB, 0xA6, 0x74, 0x00, 0x4C, 0xB1, 0x7F, 0x82, 0x99, 0x87, 0x0E, 0x5E, 0xC0,
    0x8F, 0xEE, 0x6F, 0x55, 0xF3, 0x7E, 0x08, 0x90, 0xFA, 0xB6, 0x64, 0x70, 0x47, 0x4A, 0x17, 0xA7,
    0xB5, 0x40, 0x8A, 0x38, 0xE5, 0x68, 0x3E, 0x8B, 0x69, 0xAA, 0x9B, 0x42, 0xA5, 0x10, 0x01, 0x35,
    0xFD, 0x61, 0x9E, 0xE6, 0x16, 0x9C, 0x86, 0xED, 0xCD, 0x2E, 0xFF, 0xC4, 0x5B, 0xA0, 0xAE, 0xCC,
    0x4B, 0x3B, 0x03, 0xBB, 0x1C, 0x2A, 0xAC, 0x0C, 0x3F, 0x93, 0xC7, 0x72, 0x7A, 0x09, 0x22, 0x3D,
    0x45, 0x78, 0xA9, 0xA8, 0xEA, 0xC9, 0x6A, 0xF7, 0x29, 0x91, 0xF0, 0x02, 0x18, 0x3A, 0x4E, 0x7C,
];

const CRYPT_TAB3: [u8; 288] = [
    0x73, 0x51, 0x95, 0xE1, 0x12, 0xE4, 0xC0, 0x58, 0xEE, 0xF2, 0x08, 0x1B, 0xA9, 0xFA, 0x98, 0x4C,
    0xA7, 0x33, 0xE2, 0x1B, 0xA7, 0x6D, 0xF5, 0x30, 0x97, 0x1D, 0xF3, 0x02, 0x60, 0x5A, 0x82, 0x0F,
    0x91, 0xD0, 0x9C, 0x10, 0x39, 0x7A, 0x83, 0x85, 0x3B, 0xB2, 0xB8, 0xAE, 0x0C, 0x09, 0x52, 0xEA,
    0x1C, 0xE1, 0x8D, 0x66, 0x4F, 0xF3, 0xDA, 0x92, 0x29, 0xB9, 0xD5, 0xC5, 0x77, 0x47, 0x22, 0x53,
    0x14, 0xF7, 0xAF, 0x22, 0x64, 0xDF, 0xC6, 0x72, 0x12, 0xF3, 0x75, 0xDA, 0xD7, 0xD7, 0xE5, 0x02,
    0x9E, 0xED, 0xDA, 0xDB, 0x4C, 0x47, 0xCE, 0x91, 0x06, 0x06, 0x6D, 0x55, 0x8B, 0x19, 0xC9, 0xEF,
    0x8C, 0x80, 0x1A, 0x0E, 0xEE, 0x4B, 0xAB, 0xF2, 0x08, 0x5C, 0xE9, 0x37, 0x26, 0x5E, 0x9A, 0x90,
    0x00, 0xF3, 0x0D, 0xB2, 0xA6, 0xA3, 0xF7, 0x26, 0x17, 0x48, 0x88, 0xC9, 0x0E, 0x2C, 0xC9, 0x02,
    0xE7, 0x18, 0x05, 0x4B, 0xF3, 0x39, 0xE1, 0x20, 0x02, 0x0D, 0x40, 0xC7, 0xCA, 0xB9, 0x48, 0x30,
    0x57, 0x67, 0xCC, 0x06, 0xBF, 0xAC, 0x81, 0x08, 0x24, 0x7A, 0xD4, 0x8B, 0x19, 0x8E, 0xAC, 0xB4,
    0x5A, 0x0F, 0x73, 0x13, 0xAC, 0x9E, 0xDA, 0xB6, 0xB8, 0x96, 0x5B, 0x60, 0x88, 0xE1, 0x81, 0x3F,
    0x07, 0x86, 0x37, 0x2D, 0x79, 0x14, 0x52, 0xEA, 0x73, 0xDF, 0x3D, 0x09, 0xC8, 0x25, 0x48, 0xD8,
    0x75, 0x60, 0x9A, 0x08, 0x27, 0x4A, 0x2C, 0xB9, 0xA8, 0x8B, 0x8A, 0x73, 0x62, 0x37, 0x16, 0x02,
    0xBD, 0xC1, 0x0E, 0x56, 0x54, 0x3E, 0x14, 0x5F, 0x8C, 0x8F, 0x6E, 0x75, 0x1C, 0x07, 0x39, 0x7B,
    0x4B, 0xDB, 0xD3, 0x4B, 0x1E, 0xC8, 0x7E, 0xFE, 0x3E, 0x72, 0x16, 0x83, 0x7D, 0xEE, 0xF5, 0xCA,
    0xC5, 0x18, 0xF9, 0xD8, 0x68, 0xAB, 0x38, 0x85, 0xA8, 0xF0, 0xA1, 0x73, 0x9F, 0x5D, 0x19, 0x0B,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x33, 0x72, 0x39, 0x25, 0x67, 0x26, 0x6D, 0x71,
    0x36, 0x77, 0x3C, 0x20, 0x62, 0x23, 0x68, 0x74, 0xC3, 0x82, 0xC9, 0x15, 0x57, 0x16, 0x5D, 0x81,
];

const VARIANTS: [u8; 32] = [
    0xB7, 0x74, 0x85, 0xD0, 0xCC, 0xDB, 0xCA, 0x73, 0x03, 0xFE, 0x31, 0x03, 0x52, 0xE0, 0xB7, 0x42,
    0x63, 0x16, 0xF2, 0x2A, 0x79, 0x52, 0xFF, 0x1B, 0x7A, 0x11, 0xCA, 0x1A, 0x9B, 0x40, 0xAD, 0x01,
];

const SECRET: [u8; 5] = [0x55, 0xD6, 0xC4, 0xC5, 0x28];

const PERM_CHALLENGE: [[usize; 10]; 3] = [
    [1, 3, 0, 7, 5, 2, 9, 6, 4, 8],
    [6, 1, 9, 3, 8, 5, 7, 4, 0, 2],
    [4, 0, 3, 5, 7, 2, 8, 6, 1, 9],
];

const PERM_VARIANT: [[u8; 32]; 2] = [
    [
        0x0A, 0x08, 0x0E, 0x0C, 0x0B, 0x09, 0x0F, 0x0D, 0x1A, 0x18, 0x1E, 0x1C, 0x1B, 0x19, 0x1F,
        0x1D, 0x02, 0x00, 0x06, 0x04, 0x03, 0x01, 0x07, 0x05, 0x12, 0x10, 0x16, 0x14, 0x13, 0x11,
        0x17, 0x15,
    ],
    [
        0x12, 0x1A, 0x16, 0x1E, 0x02, 0x0A, 0x06, 0x0E, 0x10, 0x18, 0x14, 0x1C, 0x00, 0x08, 0x04,
        0x0C, 0x13, 0x1B, 0x17, 0x1F, 0x03, 0x0B, 0x07, 0x0F, 0x11, 0x19, 0x15, 0x1D, 0x01, 0x09,
        0x05, 0x0D,
    ],
];

// ── Public API ──────────────────────────────────────────────────────────────

/// Perform CSS authentication with the drive.
pub fn authenticate(drive: &mut Drive) -> Result<()> {
    let scsi = drive.scsi_mut();

    // Invalidate all AGIDs
    for agid in 0..4u8 {
        let mut buf = [0u8; 4];
        let _ = scsi.execute(
            &report_key_cdb(agid, 0x3F, 0),
            crate::scsi::DataDirection::FromDevice,
            &mut buf,
            5_000,
        );
    }

    // Allocate AGID
    let mut buf = [0u8; 8];
    scsi.execute(
        &report_key_cdb(0, 0x00, 8),
        crate::scsi::DataDirection::FromDevice,
        &mut buf,
        5_000,
    )
    .map_err(|_| Error::CssAuthFailed)?;
    let agid = (buf[7] >> 6) & 0x03;

    // Step 1: Send host challenge
    let host_challenge: [u8; 10] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
    let mut hc_buf = [0u8; 16];
    hc_buf[0] = 0x00;
    hc_buf[1] = 0x0E;
    // Byte-reverse on wire
    for i in 0..10 {
        hc_buf[4 + i] = host_challenge[9 - i];
    }
    scsi.execute(
        &send_key_cdb(agid, 0x01, 16),
        crate::scsi::DataDirection::ToDevice,
        &mut hc_buf,
        5_000,
    )
    .map_err(|_| Error::CssAuthFailed)?;

    // Step 2: Get Key1 from drive
    let mut dk_buf = [0u8; 12];
    scsi.execute(
        &report_key_cdb(agid, 0x02, 12),
        crate::scsi::DataDirection::FromDevice,
        &mut dk_buf,
        5_000,
    )
    .map_err(|_| Error::CssAuthFailed)?;
    let mut key1 = [0u8; 5];
    for i in 0..5 {
        key1[i] = dk_buf[4 + (4 - i)]; // byte-reverse
    }

    // Step 3: Brute-force variant (0-31)
    let mut variant: Option<u8> = None;
    for v in 0..32u8 {
        let check = crypt_key(0, v, &host_challenge);
        if check == key1 {
            variant = Some(v);
            break;
        }
    }
    let variant = variant.ok_or(Error::CssAuthFailed)?;

    // Step 4: Get drive challenge
    let mut dc_buf = [0u8; 16];
    scsi.execute(
        &report_key_cdb(agid, 0x01, 16),
        crate::scsi::DataDirection::FromDevice,
        &mut dc_buf,
        5_000,
    )
    .map_err(|_| Error::CssAuthFailed)?;
    let mut drive_challenge = [0u8; 10];
    for i in 0..10 {
        drive_challenge[i] = dc_buf[4 + (9 - i)]; // byte-reverse
    }

    // Step 5: Compute Key2 and send it
    let key2 = crypt_key(1, variant, &drive_challenge);
    let mut hk_buf = [0u8; 12];
    hk_buf[0] = 0x00;
    hk_buf[1] = 0x0A;
    for i in 0..5 {
        hk_buf[4 + i] = key2[4 - i]; // byte-reverse
    }
    scsi.execute(
        &send_key_cdb(agid, 0x03, 12), // format 0x03 for Key2
        crate::scsi::DataDirection::ToDevice,
        &mut hk_buf,
        5_000,
    )
    .map_err(|_| Error::CssAuthFailed)?;

    Ok(())
}

// ── CSSCryptKey — the bus key challenge-response cipher ─────────────────────

/// Compute CSS bus key challenge response.
/// key_type: 0=Key1, 1=Key2, 2=bus_key
fn crypt_key(key_type: usize, variant: u8, challenge: &[u8; 10]) -> [u8; 5] {
    // Permute challenge
    let perm = &PERM_CHALLENGE[key_type];
    let mut scratch = [0u8; 10];
    for i in 0..10 {
        scratch[i] = challenge[perm[i]];
    }

    // Resolve CSS variant
    let css_variant = match key_type {
        0 => variant as usize,
        1 => PERM_VARIANT[0][variant as usize] as usize,
        _ => PERM_VARIANT[1][variant as usize] as usize,
    };

    let cse = VARIANTS[css_variant] ^ CRYPT_TAB2[css_variant];

    // LFSR init from upper 5 challenge bytes + secret
    let mut tmp1 = [0u8; 5];
    for i in 0..5 {
        tmp1[i] = scratch[5 + i] ^ SECRET[i] ^ CRYPT_TAB2[i];
    }

    let mut lfsr0: u32 = ((tmp1[0] as u32) << 17)
        | ((tmp1[1] as u32) << 9)
        | (((tmp1[2] as u32) & !7) << 1)
        | 8
        | (tmp1[2] as u32 & 7);

    let mut lfsr1: u32 = ((tmp1[3] as u32) << 9) | 0x100 | (tmp1[4] as u32);

    // Generate 30 pseudo-random bytes
    let mut bits = [0u8; 30];
    let mut carry: u32 = 0;
    for idx in (0..30).rev() {
        let mut val: u8 = 0;
        for bit in 0..8u8 {
            let lfsr0_out = ((lfsr0 >> 24) ^ (lfsr0 >> 21) ^ (lfsr0 >> 20) ^ (lfsr0 >> 12)) & 1;
            lfsr0 = ((lfsr0 << 1) | lfsr0_out) & 0x1FFFFFF;

            let lfsr1_out = ((lfsr1 >> 16) ^ (lfsr1 >> 2)) & 1;
            lfsr1 = ((lfsr1 << 1) | lfsr1_out) & 0x1FFFF;

            let combined = ((!lfsr1_out) & 1) + carry + ((!lfsr0_out) & 1);
            carry = (combined >> 1) & 1;
            val |= ((combined & 1) as u8) << bit;
        }
        bits[idx] = val;
    }

    // Six substitution-permutation rounds (NOT all identical — rounds 3,4 use CRYPT_TAB0)
    // Matches libdvdcss CryptKey() exactly.
    let mut tmp1 = [scratch[0], scratch[1], scratch[2], scratch[3], scratch[4]];
    let mut tmp2 = [0u8; 5];

    // Round 1: bits[25..29] ^ scratch -> tmp1
    {
        let mut term: u8 = 0;
        for i in (0..5usize).rev() {
            let idx = (bits[25 + i] ^ tmp1[i]) as usize;
            let idx2 = (CRYPT_TAB1[idx] ^ (!CRYPT_TAB2[idx]) ^ cse) as usize;
            tmp1[i] = CRYPT_TAB2[idx2] ^ CRYPT_TAB3[idx2] ^ term;
            term = scratch[i];
        }
        tmp1[4] ^= tmp1[0];
    }

    // Round 2: bits[20..24] ^ tmp1 -> tmp2
    {
        let mut term: u8 = 0;
        for i in (0..5usize).rev() {
            let idx = (bits[20 + i] ^ tmp1[i]) as usize;
            let idx2 = (CRYPT_TAB1[idx] ^ (!CRYPT_TAB2[idx]) ^ cse) as usize;
            tmp2[i] = CRYPT_TAB2[idx2] ^ CRYPT_TAB3[idx2] ^ term;
            term = tmp1[i];
        }
        tmp2[4] ^= tmp2[0];
    }

    // Round 3: bits[15..19] ^ tmp2 -> tmp1 (uses CRYPT_TAB0!)
    {
        let mut term: u8 = 0;
        for i in (0..5usize).rev() {
            let idx = (bits[15 + i] ^ tmp2[i]) as usize;
            let idx2 = (CRYPT_TAB1[idx] ^ (!CRYPT_TAB2[idx]) ^ cse) as usize;
            let idx3 = (CRYPT_TAB2[idx2] ^ CRYPT_TAB3[idx2] ^ term) as usize;
            tmp1[i] = CRYPT_TAB0[idx3] ^ CRYPT_TAB2[idx3];
            term = tmp2[i];
        }
        tmp1[4] ^= tmp1[0];
    }

    // Round 4: bits[10..14] ^ tmp1 -> tmp2 (uses CRYPT_TAB0!)
    {
        let mut term: u8 = 0;
        for i in (0..5usize).rev() {
            let idx = (bits[10 + i] ^ tmp1[i]) as usize;
            let idx2 = (CRYPT_TAB1[idx] ^ (!CRYPT_TAB2[idx]) ^ cse) as usize;
            let idx3 = (CRYPT_TAB2[idx2] ^ CRYPT_TAB3[idx2] ^ term) as usize;
            tmp2[i] = CRYPT_TAB0[idx3] ^ CRYPT_TAB2[idx3];
            term = tmp1[i];
        }
        tmp2[4] ^= tmp2[0];
    }

    // Round 5: bits[5..9] ^ tmp2 -> tmp1
    {
        let mut term: u8 = 0;
        for i in (0..5usize).rev() {
            let idx = (bits[5 + i] ^ tmp2[i]) as usize;
            let idx2 = (CRYPT_TAB1[idx] ^ (!CRYPT_TAB2[idx]) ^ cse) as usize;
            tmp1[i] = CRYPT_TAB2[idx2] ^ CRYPT_TAB3[idx2] ^ term;
            term = tmp2[i];
        }
        tmp1[4] ^= tmp1[0];
    }

    // Round 6: bits[0..4] ^ tmp1 -> key (output)
    let mut key = [0u8; 5];
    {
        let mut term: u8 = 0;
        for i in (0..5usize).rev() {
            let idx = (bits[i] ^ tmp1[i]) as usize;
            let idx2 = (CRYPT_TAB1[idx] ^ (!CRYPT_TAB2[idx]) ^ cse) as usize;
            key[i] = CRYPT_TAB2[idx2] ^ CRYPT_TAB3[idx2] ^ term;
            term = tmp1[i];
        }
    }

    key
}

// ── SCSI CDB builders ──────────────────────────────────────────────────────

fn report_key_cdb(agid: u8, format: u8, alloc_len: u16) -> [u8; 12] {
    let mut cdb = [0u8; 12];
    cdb[0] = crate::scsi::SCSI_REPORT_KEY;
    cdb[8] = (alloc_len >> 8) as u8;
    cdb[9] = alloc_len as u8;
    cdb[10] = (agid << 6) | (format & 0x3F);
    cdb
}

fn send_key_cdb(agid: u8, format: u8, param_len: u16) -> [u8; 12] {
    let mut cdb = [0u8; 12];
    cdb[0] = crate::scsi::SCSI_SEND_KEY;
    cdb[8] = (param_len >> 8) as u8;
    cdb[9] = param_len as u8;
    cdb[10] = (agid << 6) | (format & 0x3F);
    cdb
}

// ── Tests ───────────────────────────────────────────────────────────────────

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

    #[test]
    fn crypt_key_is_deterministic() {
        let challenge: [u8; 10] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
        for v in 0..32u8 {
            let r1 = crypt_key(0, v, &challenge);
            let r2 = crypt_key(0, v, &challenge);
            assert_eq!(r1, r2);
        }
    }

    #[test]
    fn crypt_key_varies_by_variant() {
        let challenge: [u8; 10] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
        let r0 = crypt_key(0, 0, &challenge);
        let r1 = crypt_key(0, 1, &challenge);
        assert_ne!(r0, r1);
    }

    #[test]
    fn crypt_key_varies_by_type() {
        let challenge: [u8; 10] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
        let r0 = crypt_key(0, 5, &challenge);
        let r1 = crypt_key(1, 5, &challenge);
        assert_ne!(r0, r1);
    }

    #[test]
    fn crypt_key_nonzero() {
        let challenge: [u8; 10] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
        for v in 0..32u8 {
            let r = crypt_key(0, v, &challenge);
            assert_ne!(r, [0u8; 5], "zero result for variant {}", v);
        }
    }
}