sim: add EC256 encryption key

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/enc-ec256-pub.pem b/enc-ec256-pub.pem
new file mode 100644
index 0000000..dfd21e1
--- /dev/null
+++ b/enc-ec256-pub.pem
@@ -0,0 +1,4 @@
+-----BEGIN PUBLIC KEY-----
+MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEikRzAJTJgCcxDSM2a+lpn8vFfMhE
+GpPm7n2Gpq5ek3J02eFaHJtlGithQSgCc4QSlzotoqBndwLaZxpL3ddxzA==
+-----END PUBLIC KEY-----