update comment for subgroup attack

1 files changed, 12 insertions, 0 deletions

diff --git a/readme.md b/readme.md
index 64134d3..a2d6d52 100644
--- a/readme.md
+++ b/readme.md
@@ -130,6 +130,18 @@ bool Sign::verify(const PublicKey& pub) const;
 
 Verify a public key by pop.
 
+# Check the order of a point
+
+deserializer functions check whether a point has correct order and
+the cost is heavy for especially G2.
+If you do not want to check it, then call
+```
+void blsSignatureVerifyOrder(false);
+void blsPublicKeyVerifyOrder(false);
+```
+
+cf. subgroup attack
+
 # Go
 ```
 make test_go