FranklinWH-wiki/docs/.vitepress/script/crypto/decrypt_pdf_wed.ts

function arrayBufferToBase64(buffer: ArrayBuffer): string {
  let binary = '';
  const bytes = new Uint8Array(buffer);
  const len = bytes.byteLength;

  for (let i = 0; i < len; i++) {
    binary += String.fromCharCode(bytes[i]);
  }

  return btoa(binary);
}

async function getKey(password: string): Promise<ArrayBuffer> {
  const encoder = new TextEncoder()
  const data = encoder.encode(password)
  const hash = await crypto.subtle.digest('SHA-256', data)
  return hash
}

function readUint32BE(buffer: ArrayBuffer, offset: number = 0): number {
  const view = new DataView(buffer);
  return view.getUint32(offset, false); // false 表示使用大端（Big Endian）
}

/**
 * Web端 AES-256-GCM 解密
 * @param encrypted - 加密后的数据（不包含认证标签）
 * @param keyBuffer - 原始密钥（32 字节）
 * @param ivBuffer - 初始化向量（12 字节）
 * @param authTag - 认证标签（16 字节）
 * @returns 解密后的明文字符串
 */
async function decryptAES_GCM(
  encrypted: ArrayBuffer,
  keyBuffer: ArrayBuffer,
  ivBuffer: ArrayBuffer,
  authTag: ArrayBuffer
): Promise<ArrayBuffer> {
  // 1. 导入密钥
  const key = await crypto.subtle.importKey(
    'raw',
    keyBuffer,
    'AES-GCM',
    false,
    ['decrypt']
  );

  // 2. 将认证标签附加到加密数据末尾
  const combinedData = new Uint8Array(encrypted.byteLength + authTag.byteLength);
  combinedData.set(new Uint8Array(encrypted), 0);
  combinedData.set(new Uint8Array(authTag), encrypted.byteLength);

  // 3. 解密操作
  try {
    const decrypted = await crypto.subtle.decrypt(
      {
        name: 'AES-GCM',
        iv: ivBuffer,
        tagLength: 128, // 默认的 GCM 标签长度
      },
      key,
      combinedData.buffer
    );

    // 将解密后的数据转换为字符串
    // return new TextDecoder().decode(decrypted);
    return decrypted
  } catch (error) {
    console.error('Decryption failed:', error);
    throw error;
  }
}

async function decryptGCM(url: string): Promise<Uint8Array | undefined> {
  const res = await fetch(url).catch((err) => {
    console.error('Error during fetch:', err)
    return undefined
  })
  if (!res) return undefined
  const buffer = await res.arrayBuffer().catch((err) => {
    console.error('Error during arrayBuffer:', err)
    return undefined
  })
  if (!buffer) return undefined

  const iv = buffer.slice(0, 12)
  const lenBuf = buffer.slice(buffer.byteLength - 4)
  const pLen = readUint32BE(lenBuf)
  const passwordBuffer = buffer.slice(buffer.byteLength - pLen - 4, buffer.byteLength - 4)
  const password = arrayBufferToBase64(passwordBuffer)
  const authTag = buffer.slice(buffer.byteLength - pLen - 4 - 16, buffer.byteLength - pLen - 4)
  const encrypted = buffer.slice(12, buffer.byteLength - pLen - 4 - 16)

  const key = await getKey(password).catch((err) => {
    console.error('Error during get key:', err)
    return undefined
  })
  if (!key) return undefined

  const decrypted = await decryptAES_GCM(encrypted, key, iv, authTag).catch((err) => {
    console.error('Error during decrypt:', err)
    return undefined
  })
  if (!decrypted) return undefined

  return new Uint8Array(decrypted)
}

// 解密示例
const decryptedData = await decryptGCM(withBase(props.fileUrl)).catch((err) => {
  console.error('Error during decrypt GCM:', err)
  return undefined
})
if (!decryptedData) return