Add ChangeLog entry
diff --git a/ChangeLog b/ChangeLog
index 4c09593..bed180d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
mbed TLS ChangeLog (Sorted per branch, date)
+= mbed TLS 2.x.x branch released xxxx-xx-xx
+
+Security
+ * When writing a private EC key, use a constant size for the private
+ value, as specified in RFC 5915. Previously, the value was written
+ as an ASN.1 INTEGER, which caused the size of the key to leak
+ about 1 bit of information on average and could cause the value to be
+ 1 byte too large for the output buffer.
+
= mbed TLS 2.12.0 branch released 2018-07-25
Security
