Merge "Update ProtectedData DKCertChain to use X.509"

     *     SignerName = tstr

     *

     *     DKCertChain = [

     *         2* Certificate           // Root -> ... -> Leaf. "Root" is the vendor self-signed

     *         2* X509Certificate       // Root -> ... -> Leaf. "Root" is the vendor self-signed

     *                                  // cert, "Leaf" contains DK_pub. There may also be

     *                                  // intermediate certificates between Root and Leaf.

     *     ]

     *

     *     // Certificates may be either:

     *     // 1. COSE_Sign1, with payload containing PubKeyEd25519 or PubKeyECDSA256

     *     // 2. a bstr containing a DER-encoded X.509 certificate (RSA, NIST P-curve, or edDSA)

     *     Certificate = COSE_Sign1 / bstr

     *     // A bstr containing a DER-encoded X.509 certificate (RSA, NIST P-curve, or edDSA)

     *     X509Certificate = bstr

     *

     *     // The SignedMac, which authenticates the MAC key that is used to authenticate the

     *     // keysToSign.