RobRichards\XMLSecLibs\XMLSecurityKey::getSymmetricKeySize PHP Method

    public function getSymmetricKeySize()
    {
        if (!isset($this->cryptParams['keysize'])) {
            return null;
        }
        return $this->cryptParams['keysize'];
    }

 /**
  * @param XMLSecurityKey $inputKey
  *
  * @throws \Exception
  */
 protected function decryptSymmetricKey(XMLSecurityKey $inputKey)
 {
     /** @var XMLSecEnc $encKey */
     $encKey = $this->symmetricKeyInfo->encryptedCtx;
     $this->symmetricKeyInfo->key = $inputKey->key;
     $keySize = $this->symmetricKey->getSymmetricKeySize();
     if ($keySize === null) {
         // To protect against "key oracle" attacks, we need to be able to create a
         // symmetric key, and for that we need to know the key size.
         throw new LightSamlSecurityException(sprintf("Unknown key size for encryption algorithm: '%s'", $this->symmetricKey->type));
     }
     /** @var string $key */
     $key = $encKey->decryptKey($this->symmetricKeyInfo);
     if (false == is_string($key)) {
         throw new \LogicException('Expected string');
     }
     if (strlen($key) != $keySize) {
         throw new LightSamlSecurityException(sprintf("Unexpected key size of '%s' bits for encryption algorithm '%s', expected '%s' bits size", strlen($key) * 8, $this->symmetricKey->type, $keySize));
     }
     $this->symmetricKey->loadkey($key);
 }