rsa: Verify RSA padding programatically
Padding verification was done against static SHA/RSA pair arrays which
take up a lot of static memory, are mostly 0xff, and cannot be reused
for additional SHA/RSA pairings. The padding can be easily computed
according to PKCS#1v2.1 as:
EM = 0x00 || 0x01 || PS || 0x00 || T
where PS is (emLen - tLen - 3) octets of 0xff and T is DER encoding
of the hash.
Store DER prefix in checksum_algo and create rsa_verify_padding
function to handle verification of a message for any SHA/RSA pairing.
Signed-off-by: Andrew Duda <aduda@meraki.com>
Signed-off-by: aduda <aduda@meraki.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/u-boot/sha256.h b/include/u-boot/sha256.h
index beadab3..9aa1251 100644
--- a/include/u-boot/sha256.h
+++ b/include/u-boot/sha256.h
@@ -2,6 +2,9 @@
#define _SHA256_H
#define SHA256_SUM_LEN 32
+#define SHA256_DER_LEN 19
+
+extern const uint8_t sha256_der_prefix[];
/* Reset watchdog each time we process this many bytes */
#define CHUNKSZ_SHA256 (64 * 1024)