Add ChangeLog entry
diff --git a/ChangeLog b/ChangeLog
index c92e429..7074eb2 100644
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@@ -2,6 +2,13 @@
= mbed TLS 2.16.x branch released xxxx-xx-xx
+Security
+ * Fix side channel vulnerability in ECDSA. Our bignum implementation is not
+ constant time/constant trace, so side channel attacks can retrieve the
+ blinded value, factor it (as it is smaller than RSA keys and not guaranteed
+ to have only large prime factors), and then, by brute force, recover the
+ key. Reported by Alejandro Cabrera Aldaya and Billy Brumley.
+
Bugfix
* Remove redundant line for getting the bitlen of a bignum, since the variable
holding the returned value is overwritten a line after.