Function decryptWithPrivateKey

packages/encryption/src/encryption.ts:104–178

(
  envelope: EncryptedEnvelope,
  privateKeyPem: string | Buffer,
  aad?: string
)

 * 2. Decrypt data using decrypted DEK
 */
export function decryptWithPrivateKey(
  envelope: EncryptedEnvelope,
  privateKeyPem: string | Buffer,
  aad?: string
): string {
  if (!privateKeyPem) {
    throw new EncryptionConfigurationError('Private key parameter is required');
  }

  if (!envelope || typeof envelope !== 'object') {
    throw new EncryptionFormatError('Invalid envelope: must be an object');
  }

  if (envelope.algorithm !== 'rsa-aes-256-gcm') {
    throw new EncryptionFormatError(
      `Unsupported algorithm: ${String(envelope.algorithm)}. Expected: rsa-aes-256-gcm`
    );
  }

  if (envelope.version !== 1) {
    throw new EncryptionFormatError(
      `Unsupported version: ${String(envelope.version)}. Expected: 1`
    );
  }

  if (!envelope.encryptedData || !envelope.encryptedDEK) {
    throw new EncryptionFormatError('Invalid envelope: missing encryptedData or encryptedDEK');
  }

  try {
    // Decrypt DEK using private key
    const encryptedDEKBuffer = Buffer.from(envelope.encryptedDEK, 'base64');
    const dekBuffer = privateDecrypt(
      {
        key: privateKeyPem,
        padding: constants.RSA_PKCS1_OAEP_PADDING,
        oaepHash: 'sha256',
      },
      encryptedDEKBuffer
    );

    // Decrypt data using decrypted DEK
    const encryptedDataBuffer = Buffer.from(envelope.encryptedData, 'base64');

    // Extract iv (first 16 bytes), encrypted data, and authTag (last 16 bytes)
    if (encryptedDataBuffer.length < 32) {
      throw new EncryptionFormatError('Invalid encrypted data: too short');
    }

    const iv = encryptedDataBuffer.subarray(0, 16);
    const authTag = encryptedDataBuffer.subarray(encryptedDataBuffer.length - 16);
    const encryptedData = encryptedDataBuffer.subarray(16, encryptedDataBuffer.length - 16);

    const decipher = createDecipheriv('aes-256-gcm', dekBuffer, iv);
    if (aad !== undefined) {
      decipher.setAAD(Buffer.from(aad, 'utf8'));
    }
    decipher.setAuthTag(authTag);