add some explicit instructions on determining key type in a cert (#3596)
* add some explicit instructions on determining key type in a cert
* can't call it a CSR
diff --git a/docs/x509/tutorial.rst b/docs/x509/tutorial.rst
index 372d78a..d34b350 100644
--- a/docs/x509/tutorial.rst
+++ b/docs/x509/tutorial.rst
@@ -152,3 +152,20 @@
And now we have a private key and certificate that can be used for local
testing.
+
+Determining Certificate or Certificate Signing Request Key Type
+---------------------------------------------------------------
+
+Certificates and certificate signing requests can be issued with multiple
+key types. You can determine what the key type is by using ``isinstance``
+checks:
+
+.. code-block:: pycon
+
+ >>> public_key = cert.public_key()
+ >>> if isinstance(public_key, rsa.RSAPublicKey):
+ ... # Do something RSA specific
+ ... elif isinstance(public_key, ec.EllipticCurvePublicKey):
+ ... # Do something EC specific
+ ... else:
+ ... # Remember to handle this case