Add blinding to an ECDSA signature

Keegan Ryan (NCC Group) has demonstrated a side channel attack on an
ECDSA signature operation. During signing the signer calculates:

s:= k^-1 * (m + r * priv_key) mod order

The addition operation above provides a sufficient signal for a
flush+reload attack to derive the private key given sufficient signature
operations.

As a mitigation (based on a suggestion from Keegan) we add blinding to
the operation so that:

s := k^-1 * blind^-1 (blind * m + blind * r * priv_key) mod order

Since this attack is a localhost side channel only no CVE is assigned.

Reviewed-by: Rich Salz <rsalz@openssl.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/CHANGES b/CHANGES
index 7a478521c1..fe3e13aa0d 100644
--- a/CHANGES
+++ b/CHANGES
@@ -8,6 +8,10 @@
  release branch.
 
  Changes between 1.1.0h and 1.1.1 [xx XXX xxxx]
+  *) Add blinding to an ECDSA signature to protect against side channel attacks
+     discovered by Keegan Ryan (NCC Group).
+     [Matt Caswell]
+
   *) Enforce checking in the pkeyutl command line app to ensure that the input
      length does not exceed the maximum supported digest length when performing
      a sign, verify or verifyrecover operation.