Implement generalised RSA public exponents for verified boot

Remove the verified boot limitation that only allows a single
RSA public exponent of 65537 (F4).  This change allows use with
existing PKI infrastructure and has been tested with HSM-based
PKI.

Change the configuration OF tree format to store the RSA public
exponent as a 64 bit integer and implement backward compatibility
for verified boot configuration trees without this extra field.

Parameterise vboot_test.sh to test different public exponents.

Mathematics and other hard work by Andrew Bott.

Tested with the following public exponents: 3, 5, 17, 257, 39981,
50457, 65537 and 4294967297.

Signed-off-by: Andrew Bott <Andrew.Bott@ipaccess.com>
Signed-off-by: Andrew Wishart <Andrew.Wishart@ipaccess.com>
Signed-off-by: Neil Piercy <Neil.Piercy@ipaccess.com>
Signed-off-by: Michael van der Westhuizen <michael@smart-africa.com>
Cc: Simon Glass <sjg@chromium.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/doc/uImage.FIT/signature.txt b/doc/uImage.FIT/signature.txt
index a6ab543de4..b2f89fcc65 100644
--- a/doc/uImage.FIT/signature.txt
+++ b/doc/uImage.FIT/signature.txt
@@ -66,7 +66,8 @@ Creating an RSA key and certificate
 -----------------------------------
 To create a new public key, size 2048 bits:
 
-$ openssl genrsa -F4 -out keys/dev.key 2048
+$ openssl genpkey -algorithm RSA -out keys/dev.key \
+    -pkeyopt rsa_keygen_bits:2048 -pkeyopt rsa_keygen_pubexp:65537
 
 To create a certificate for this:
 
@@ -159,6 +160,7 @@ For RSA the following are mandatory:
 
 - rsa,num-bits: Number of key bits (e.g. 2048)
 - rsa,modulus: Modulus (N) as a big-endian multi-word integer
+- rsa,exponent: Public exponent (E) as a 64 bit unsigned integer
 - rsa,r-squared: (2^num-bits)^2 as a big-endian multi-word integer
 - rsa,n0-inverse: -1 / modulus[0] mod 2^32