<?php
/*************************************************************
# 076 License

Copyright (c) テクニカル諏訪子

Permission is hereby granted to any person obtaining a copy of the software
Little Beast (the "Software") to use, modify, merge, copy, publish, distribute,
sublicense, and/or sell copies of the Software, subject to the following conditions:

    1. **Origin Attribution**:
       - You must not misrepresent the origin of the Software; you must not claim
         you created the original Software.
       - If the Software is used in a product, you must either:
         a. Provide clear attribution in the product's documentation, user interface,
            or other visible areas, **OR**
         b. Pay the original developers a fee they specify in writing.
    2. **Usage Restriction**:
       - The Software, or any derivative works, dependencies, or libraries
         incorporating it, must not be used for censorship or to suppress freedom of
         speech, expression, or creativity. Prohibited uses include, but are not
         limited to:
         - Censorship of so-called "hate speech", visuals, non-mainstream opinions,
           ideas, or objective reality.
         - Tools or systems designed to restrict access to information or
           artistic works.
    3. **Notice Preservation**:
       - This license and the above copyright notice must remain intact in all copies
         of the source code.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
namespace Std\Lib\Crypto;

/**
 * ChaCha20-Poly1305（RFC 8439のAEAD）
 *
 * 例：
 *   $c = new ChaCha20($key32);
 *   $sealed = $c->seal($nonce12, $plain, $aad);   // 暗号文||タグ（16バイト）
 *   $plain = $c->open($nonce12, $sealed, $aad);   // 改ざんされていればnull
 */
class ChaCha20 {
  private array $k;

  /**
   * @param string $key  32バイト
   */
  public function __construct(string $key) {
    if (strlen($key) !== 32) throw new \InvalidArgumentException('ChaCha20：鍵は32バイト');
    $this->k = array_values(unpack('V8', $key));
  }

  /**
   * 暗号化する（AEAD）
   *
   * @param string $nonce  12バイト
   * @param string $plain  平文
   * @param string $aad  追加の認証データ
   * @return string  暗号文||タグ（16バイト）
   */
  public function seal(string $nonce, string $plain, string $aad = ''): string {
    if (strlen($nonce) !== 12) throw new \InvalidArgumentException('ChaCha20：ノンスは12バイト');
    $ct = $this->xor($nonce, $plain, 1);
    return $ct.$this->mac($nonce, $ct, $aad);
  }

  /**
   * 復号する（AEAD）
   *
   * @return string|null  平文、改ざんされていればnull
   */
  public function open(string $nonce, string $sealed, string $aad = ''): ?string {
    if (strlen($nonce) !== 12 || strlen($sealed) < 16) return null;
    $ct = substr($sealed, 0, -16);
    if (!hash_equals($this->mac($nonce, $ct, $aad), substr($sealed, -16))) return null;
    return $this->xor($nonce, $ct, 1);
  }

  /**
   * 鍵ストリームとXORする（ChaCha20だけ）
   *
   * @param string $nonce  12バイト
   * @param string $data  データ
   * @param int $counter  最初のブロックのカウンタ
   * @return string
   */
  public function xor(string $nonce, string $data, int $counter = 0): string {
    $len = strlen($data);
    if ($len === 0) return '';
    $n = unpack('V3', $nonce);
    $ks = '';
    for ($i = 0, $blocks = intdiv($len + 63, 64); $i < $blocks; $i++) {
      $ks .= $this->block(($counter + $i) & 0xFFFFFFFF, $n[1], $n[2], $n[3]);
    }
    return $data ^ substr($ks, 0, $len);
  }

  /** Poly1305のタグ（鍵はカウンタ0のブロック） */
  private function mac(string $nonce, string $ct, string $aad): string {
    $n = unpack('V3', $nonce);
    $key = substr($this->block(0, $n[1], $n[2], $n[3]), 0, 32);
    $pad = fn(string $s): string => strlen($s) % 16 ? str_repeat("\0", 16 - strlen($s) % 16) : '';
    return self::poly1305($key, $aad.$pad($aad).$ct.$pad($ct).pack('P2', strlen($aad), strlen($ct)));
  }

  /**
   * Poly1305（RFC 8439 2.5、26ビットの5つの整数で計算する）
   *
   * @param string $key  32バイト（r||s）
   * @param string $msg  メッセージ
   * @return string  16バイト
   */
  public static function poly1305(string $key, string $msg): string {
    $m = 0x3FFFFFF;
    [, $t0, $t1, $t2, $t3] = unpack('V4', $key);
    $r0 = $t0 & 0x3FFFFFF;
    $r1 = (($t0 >> 26) | ($t1 << 6)) & 0x3FFFF03;
    $r2 = (($t1 >> 20) | ($t2 << 12)) & 0x3FFC0FF;
    $r3 = (($t2 >> 14) | ($t3 << 18)) & 0x3F03FFF;
    $r4 = ($t3 >> 8) & 0x00FFFFF;
    $s1 = $r1 * 5;
    $s2 = $r2 * 5;
    $s3 = $r3 * 5;
    $s4 = $r4 * 5;
    $h0 = $h1 = $h2 = $h3 = $h4 = 0;

    $len = strlen($msg);
    $full = $len - $len % 16;
    for ($i = 0; $i < $len; $i += 16) {
      if ($i < $full) {
        [, $t0, $t1, $t2, $t3] = unpack('V4', $msg, $i);
        $hibit = 1 << 24;
      } else {
        // 最後の短いブロック：1バイトの1を足して、0で埋める
        [, $t0, $t1, $t2, $t3] = unpack('V4', str_pad(substr($msg, $i)."\x01", 16, "\0"));
        $hibit = 0;
      }
      $h0 += $t0 & $m;
      $h1 += (($t0 >> 26) | ($t1 << 6)) & $m;
      $h2 += (($t1 >> 20) | ($t2 << 12)) & $m;
      $h3 += (($t2 >> 14) | ($t3 << 18)) & $m;
      $h4 += ($t3 >> 8) | $hibit;

      $d0 = $h0 * $r0 + $h1 * $s4 + $h2 * $s3 + $h3 * $s2 + $h4 * $s1;
      $d1 = $h0 * $r1 + $h1 * $r0 + $h2 * $s4 + $h3 * $s3 + $h4 * $s2;
      $d2 = $h0 * $r2 + $h1 * $r1 + $h2 * $r0 + $h3 * $s4 + $h4 * $s3;
      $d3 = $h0 * $r3 + $h1 * $r2 + $h2 * $r1 + $h3 * $r0 + $h4 * $s4;
      $d4 = $h0 * $r4 + $h1 * $r3 + $h2 * $r2 + $h3 * $r1 + $h4 * $r0;

      $c = $d0 >> 26; $h0 = $d0 & $m;
      $d1 += $c; $c = $d1 >> 26; $h1 = $d1 & $m;
      $d2 += $c; $c = $d2 >> 26; $h2 = $d2 & $m;
      $d3 += $c; $c = $d3 >> 26; $h3 = $d3 & $m;
      $d4 += $c; $c = $d4 >> 26; $h4 = $d4 & $m;
      $h0 += $c * 5; $c = $h0 >> 26; $h0 &= $m;
      $h1 += $c;
    }

    // 完全に繰り上げる
    $c = $h1 >> 26; $h1 &= $m;
    $h2 += $c; $c = $h2 >> 26; $h2 &= $m;
    $h3 += $c; $c = $h3 >> 26; $h3 &= $m;
    $h4 += $c; $c = $h4 >> 26; $h4 &= $m;
    $h0 += $c * 5; $c = $h0 >> 26; $h0 &= $m;
    $h1 += $c;

    // h - p（h >= pならこちら）
    $g0 = $h0 + 5; $c = $g0 >> 26; $g0 &= $m;
    $g1 = $h1 + $c; $c = $g1 >> 26; $g1 &= $m;
    $g2 = $h2 + $c; $c = $g2 >> 26; $g2 &= $m;
    $g3 = $h3 + $c; $c = $g3 >> 26; $g3 &= $m;
    $g4 = $h4 + $c - (1 << 26);
    if ($g4 >= 0) {
      [$h0, $h1, $h2, $h3, $h4] = [$g0, $g1, $g2, $g3, $g4];
    }

    // h + s（mod 2^128）
    $w0 = ($h0 | ($h1 << 26)) & 0xFFFFFFFF;
    $w1 = (($h1 >> 6) | ($h2 << 20)) & 0xFFFFFFFF;
    $w2 = (($h2 >> 12) | ($h3 << 14)) & 0xFFFFFFFF;
    $w3 = (($h3 >> 18) | ($h4 << 8)) & 0xFFFFFFFF;
    [, $p0, $p1, $p2, $p3] = unpack('V4', $key, 16);
    $f = $w0 + $p0; $w0 = $f & 0xFFFFFFFF;
    $f = $w1 + $p1 + ($f >> 32); $w1 = $f & 0xFFFFFFFF;
    $f = $w2 + $p2 + ($f >> 32); $w2 = $f & 0xFFFFFFFF;
    $f = $w3 + $p3 + ($f >> 32); $w3 = $f & 0xFFFFFFFF;
    return pack('V4', $w0, $w1, $w2, $w3);
  }

  /** ChaCha20のブロック関数（RFC 8439 2.3） */
  private function block(int $counter, int $n0, int $n1, int $n2): string {
    [$k0, $k1, $k2, $k3, $k4, $k5, $k6, $k7] = $this->k;
    $x0 = 0x61707865; $x1 = 0x3320646e; $x2 = 0x79622d32; $x3 = 0x6b206574;
    $x4 = $k0; $x5 = $k1; $x6 = $k2; $x7 = $k3; $x8 = $k4; $x9 = $k5; $x10 = $k6; $x11 = $k7;
    $x12 = $counter; $x13 = $n0; $x14 = $n1; $x15 = $n2;
    $m = 0xFFFFFFFF;

    for ($i = 0; $i < 10; $i++) {
      // 列
      $x0 = ($x0 + $x4) & $m; $x12 ^= $x0; $x12 = (($x12 << 16) | ($x12 >> 16)) & $m;
      $x8 = ($x8 + $x12) & $m; $x4 ^= $x8; $x4 = (($x4 << 12) | ($x4 >> 20)) & $m;
      $x0 = ($x0 + $x4) & $m; $x12 ^= $x0; $x12 = (($x12 << 8) | ($x12 >> 24)) & $m;
      $x8 = ($x8 + $x12) & $m; $x4 ^= $x8; $x4 = (($x4 << 7) | ($x4 >> 25)) & $m;
      $x1 = ($x1 + $x5) & $m; $x13 ^= $x1; $x13 = (($x13 << 16) | ($x13 >> 16)) & $m;
      $x9 = ($x9 + $x13) & $m; $x5 ^= $x9; $x5 = (($x5 << 12) | ($x5 >> 20)) & $m;
      $x1 = ($x1 + $x5) & $m; $x13 ^= $x1; $x13 = (($x13 << 8) | ($x13 >> 24)) & $m;
      $x9 = ($x9 + $x13) & $m; $x5 ^= $x9; $x5 = (($x5 << 7) | ($x5 >> 25)) & $m;
      $x2 = ($x2 + $x6) & $m; $x14 ^= $x2; $x14 = (($x14 << 16) | ($x14 >> 16)) & $m;
      $x10 = ($x10 + $x14) & $m; $x6 ^= $x10; $x6 = (($x6 << 12) | ($x6 >> 20)) & $m;
      $x2 = ($x2 + $x6) & $m; $x14 ^= $x2; $x14 = (($x14 << 8) | ($x14 >> 24)) & $m;
      $x10 = ($x10 + $x14) & $m; $x6 ^= $x10; $x6 = (($x6 << 7) | ($x6 >> 25)) & $m;
      $x3 = ($x3 + $x7) & $m; $x15 ^= $x3; $x15 = (($x15 << 16) | ($x15 >> 16)) & $m;
      $x11 = ($x11 + $x15) & $m; $x7 ^= $x11; $x7 = (($x7 << 12) | ($x7 >> 20)) & $m;
      $x3 = ($x3 + $x7) & $m; $x15 ^= $x3; $x15 = (($x15 << 8) | ($x15 >> 24)) & $m;
      $x11 = ($x11 + $x15) & $m; $x7 ^= $x11; $x7 = (($x7 << 7) | ($x7 >> 25)) & $m;
      // 対角線
      $x0 = ($x0 + $x5) & $m; $x15 ^= $x0; $x15 = (($x15 << 16) | ($x15 >> 16)) & $m;
      $x10 = ($x10 + $x15) & $m; $x5 ^= $x10; $x5 = (($x5 << 12) | ($x5 >> 20)) & $m;
      $x0 = ($x0 + $x5) & $m; $x15 ^= $x0; $x15 = (($x15 << 8) | ($x15 >> 24)) & $m;
      $x10 = ($x10 + $x15) & $m; $x5 ^= $x10; $x5 = (($x5 << 7) | ($x5 >> 25)) & $m;
      $x1 = ($x1 + $x6) & $m; $x12 ^= $x1; $x12 = (($x12 << 16) | ($x12 >> 16)) & $m;
      $x11 = ($x11 + $x12) & $m; $x6 ^= $x11; $x6 = (($x6 << 12) | ($x6 >> 20)) & $m;
      $x1 = ($x1 + $x6) & $m; $x12 ^= $x1; $x12 = (($x12 << 8) | ($x12 >> 24)) & $m;
      $x11 = ($x11 + $x12) & $m; $x6 ^= $x11; $x6 = (($x6 << 7) | ($x6 >> 25)) & $m;
      $x2 = ($x2 + $x7) & $m; $x13 ^= $x2; $x13 = (($x13 << 16) | ($x13 >> 16)) & $m;
      $x8 = ($x8 + $x13) & $m; $x7 ^= $x8; $x7 = (($x7 << 12) | ($x7 >> 20)) & $m;
      $x2 = ($x2 + $x7) & $m; $x13 ^= $x2; $x13 = (($x13 << 8) | ($x13 >> 24)) & $m;
      $x8 = ($x8 + $x13) & $m; $x7 ^= $x8; $x7 = (($x7 << 7) | ($x7 >> 25)) & $m;
      $x3 = ($x3 + $x4) & $m; $x14 ^= $x3; $x14 = (($x14 << 16) | ($x14 >> 16)) & $m;
      $x9 = ($x9 + $x14) & $m; $x4 ^= $x9; $x4 = (($x4 << 12) | ($x4 >> 20)) & $m;
      $x3 = ($x3 + $x4) & $m; $x14 ^= $x3; $x14 = (($x14 << 8) | ($x14 >> 24)) & $m;
      $x9 = ($x9 + $x14) & $m; $x4 ^= $x9; $x4 = (($x4 << 7) | ($x4 >> 25)) & $m;
    }

    return pack('V16',
      ($x0 + 0x61707865) & $m, ($x1 + 0x3320646e) & $m, ($x2 + 0x79622d32) & $m, ($x3 + 0x6b206574) & $m,
      ($x4 + $k0) & $m, ($x5 + $k1) & $m, ($x6 + $k2) & $m, ($x7 + $k3) & $m,
      ($x8 + $k4) & $m, ($x9 + $k5) & $m, ($x10 + $k6) & $m, ($x11 + $k7) & $m,
      ($x12 + $counter) & $m, ($x13 + $n0) & $m, ($x14 + $n1) & $m, ($x15 + $n2) & $m);
  }
}