Fix leakage of projective coordinates in ECC

See the comments in the code for how an attack would go, and the ChangeLog
entry for an impact assessment. (For ECDSA, leaking a few bits of the scalar
over several signatures translates to full private key recovery using a
lattice attack.)

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/ChangeLog b/ChangeLog
index bcceebb..491b86a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,13 @@
    * Deprecate MBEDTLS_SSL_HW_RECORD_ACCEL that enables function hooks in the
      SSL module for hardware acceleration of individual records.
 
+Security
+   * Fix side channel in ECC code that allowed an adversary with access to
+     precise enough timing and memory access information (typically an
+     untrusted operating system attacking a secure enclave) to fully recover
+     an ECDSA private key. Found and reported by Alejandro Cabrera Aldaya,
+     Billy Brumley and Cesar Pereida Garcia. CVE-2020-10932
+
 Bugfix
    * Fix compilation failure when both MBEDTLS_SSL_PROTO_DTLS and
      MBEDTLS_SSL_HW_RECORD_ACCEL are enabled.