class Aws::S3::Encryption::KmsCipherProvider

def encryption_cipher
  encryption_context = { "kms_cmk_id" => @kms_key_id }
  key_data = @kms_client.generate_data_key(
    key_id: @kms_key_id,
    encryption_context: encryption_context,
    key_spec: 'AES_256',
  )
  cipher = Utils.aes_encryption_cipher(:CBC)
  cipher.key = key_data.plaintext
  envelope = {
    'x-amz-key-v2' => encode64(key_data.ciphertext_blob),
    'x-amz-iv' => encode64(cipher.iv = cipher.random_iv),
    'x-amz-cek-alg' => 'AES/CBC/PKCS5Padding',
    'x-amz-wrap-alg' => 'kms',
    'x-amz-matdesc' => Json.dump(encryption_context)
  }
  [envelope, cipher]
end