public static TpmPrivate GetPlaintextPrivate(Tpm2 tpm, TpmHandle key, PolicyTree policy)
{
AuthSession sess = tpm.StartAuthSessionEx(TpmSe.Policy, policy.HashAlg);
sess.RunPolicy(tpm, policy);
TpmPrivate privPlain = null;
byte[] symSeed;
tpm[sess]._ExpectResponses(TpmRc.Success, TpmRc.Attributes)
.Duplicate(key, TpmRh.Null, null, new SymDefObject(),
out privPlain, out symSeed);
Debug.Assert(!tpm._LastCommandSucceeded() || symSeed.Length == 0);
tpm.FlushContext(sess);
return(Globs.IsEmpty(privPlain.buffer) ? null : privPlain);
}
/// <summary>
/// The callback to sign the TpmPolicySignature challenge from the TPM.
/// </summary>
/// <param name="policyTree">The policy tree to check.</param>
/// <param name="ace">The policy element (TpmPolicySignature) to evaluate.</param>
/// <param name="nonceTpm">The nonce from the TPM.</param>
/// <returns>Signature of the nonce.</returns>
public static ISignatureUnion SignerCallback(PolicyTree policyTree, TpmPolicySigned ace,
byte[] nonceTpm, out TpmPublic verificationKey)
{
//
// This function checks the parameters of the associated TpmPolicySigned
// ACE, and if they are those expected the TPM challenge is signed.
// Note that policy expressions are often obtained from untrustworthy
// sources, so it is important for key-holders to check what they
// are bing asked to do before signing anything.
//
//
// The policy just contains the name of the signature verification key, however the
// TPM needs the actual public key to verify the signature. Check that the name
// matches, and if it does return the public key.
//
byte[] expectedName = _publicSigningKey.GetPublicParms().GetName();
if (!expectedName.SequenceEqual(ace.AuthObjectName))
{
throw new Exception("Unexpected name in policy.");
}
verificationKey = _publicSigningKey.GetPublicParms();
//
// Check that the key is the one that we expect
//
if (ace.NodeId != "Signing Key 1")
{
throw new Exception("Unrecognized key");
}
//
// Check that nonceTom is not null (otherwise anything we sign can
// be used for any session).
//
if (Globs.IsEmpty(nonceTpm))
{
throw new Exception("Sign challenges with expiration time need nonce.");
}
//
// Check PolicyRef and cpHash are what we want to sign
//
if (!Globs.IsEmpty(ace.CpHash))
{
throw new Exception("I only sign null-cpHash");
}
if (!ace.PolicyRef.SequenceEqual(new byte[] { 1, 2, 3, 4 }))
{
throw new Exception("Incorrect PolicyRef");
}
//
// And finally check that the expiration is set correctly. Check for
// positive values (simple signing policy) and negative values (sining
// policy with ticket).
//
if (ace.ExpirationTime != _expectedExpirationTime)
{
throw new Exception("Unexpected expiration time");
}
//
// Everything is OK, so get a formatted bloc containing the challenge
// data and then sign it.
//
byte[] dataToSign = PolicyTree.PackDataToSign(ace.ExpirationTime, nonceTpm,
ace.CpHash, ace.PolicyRef);
return(_publicSigningKey.Sign(dataToSign));
}