Update NIST urls in docs (#3418)
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index 1fd5a54..a3b9fea 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -650,7 +650,7 @@
.. _`described by Colin Percival`: http://www.daemonology.net/blog/2009-06-11-cryptographic-right-answers.html
.. _`recommends a 96-bit IV length`: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf
-.. _`NIST SP-800-38D`: http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf
+.. _`NIST SP-800-38D`: http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38D.pdf
.. _`Communications Security Establishment`: https://www.cse-cst.gc.ca
.. _`encrypt`: https://ssd.eff.org/en/module/what-encryption
.. _`CRYPTREC`: https://www.cryptrec.go.jp/english/