Add changelog for mbedtls_ecdsa_sign fix
diff --git a/ChangeLog b/ChangeLog
index ded60d3..f350f59 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -17,6 +17,8 @@
    * Fix leap year calculation in x509_date_is_valid() to ensure that invalid
      dates on leap years with 100 and 400 intervals are handled correctly. Found
      by Nicholas Wilson. #694
+   * Add a check for invalid private parameters in mbedtls_ecdsa_sign.
+     Reported by Yolan Romailler.
 
 = mbed TLS 2.6.0 branch released 2017-08-10