Update crypto submodule

Includes PRs #6, #18, #19.
diff --git a/crypto b/crypto
index 54c139f..0b6b871 160000
--- a/crypto
+++ b/crypto
@@ -1 +1 @@
-Subproject commit 54c139f1418937588098b0435dbd8de85fe40223
+Subproject commit 0b6b87105624b52f1c7c2f9ac4e8e2ff977a58f9