tpm2: add support for padding-only RSASSA

Perform PKCS1-padding-only signing for RSASSA if hashing algorithm is
TPM_ALG_NULL in TPM2_Sign parameters and in the key public area.

This feature is guarded by SUPPORT_PADDING_ONLY_RSASSA macro.

BUG=chrome-os-partner:60967
BRANCH=none
TEST=On a unowned machine with TPM2: corp enroll, login, install
     a network certificate (gECC or GMC), then:
     a) retrieve the public key from the installed certificate
       LIBCHAPS=`ls /usr/lib**/libchaps.so`
       CERTID=`pkcs11-tool --module=$LIBCHAPS --slot=1 --type=cert \
               -O | grep "ID:" | awk '{print $2}'`
       pkcs11-tool --module=$LIBCHAPS --slot=1 --id=$CERTID \
                   --type=cert -r > /tmp/cert
       openssl x509 -inform der -pubkey -noout -in /tmp/cert > /tmp/pub.key
     b) sign a sample text using the private key for the certificate and
        MD5-RSA-PKCS mechanism, not supported by TPM2_Sign command:
       echo "ABCDEF" > /tmp/1.txt
       pkcs11-tool --module=$LIBCHAPS --slot=1 --id=$CERTID --sign \
                 -i /tmp/1.txt -o /tmp/1.sig -m MD5-RSA-PKCS
     c) verify signature:
       openssl dgst -md5 -verify /tmp/pub.key -signature /tmp/1.sig /tmp/1.txt
     Step (b) should succeed and step (c) should return "Verified OK".

Change-Id: Iefc85d163089d6f7e09b3e7a41e1df33ba88fa3b
Signed-off-by: Andrey Pronin <apronin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/420811
Reviewed-by: Nagendra Modadugu <ngm@google.com>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-by: Darren Krahn <dkrahn@chromium.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/Sign.c b/Sign.c
index f0e29f9..10b673b 100644
--- a/Sign.c
+++ b/Sign.c
@@ -63,7 +63,11 @@ TPM2_Sign(
    // NOTE: this does not guarantee that the 'digest' is actually produced using
    // the indicated hash algorithm, but at least it might be.
    {
-       if(       in->digest.t.size
+       if(
+#if defined(SUPPORT_PADDING_ONLY_RSASSA) && SUPPORT_PADDING_ONLY_RSASSA == YES
+           in->inScheme.details.any.hashAlg != TPM_ALG_NULL &&
+#endif
+           in->digest.t.size
              != CryptGetHashDigestSize(in->inScheme.details.any.hashAlg))
              return TPM_RC_SIZE + RC_Sign_digest;
    }