void ExternalKeyImportSample(Tpm2 tpm, TestContext testCtx)
{
// Create a software key (external to any TPM).
int keySize = 2048;
var externalRsaKey = new RawRsa(keySize);
// When an external key comes from a cert, one would need to extract the key size and
// byte buffers representing public and private parts of the key from the cert, an use
// them directly in the call to ImportExternalRsaKey() below (i.e. no RawRsa object is
// necessary).
// Signing scheme to use (it may come from the key's cert)
TpmAlgId sigHashAlg = Substrate.Random(TpmCfg.HashAlgs);
var sigScheme = new SchemeRsassa(sigHashAlg);
// An arbitrary external key would not have TPM key attributes associated with it.
// Yet some of them may be inferred from the cert based on the declared key purpose
// (ObjectAttr.Sign below). The others are defined by the intended TPM key usage
// scenarios, e.g. ObjectAttr.UserWithAuth tells TPM to allow key usage authorization
// using an auth value (random byte buffer) in a password or an HMAC session.
ObjectAttr keyAttrs = ObjectAttr.Sign | ObjectAttr.UserWithAuth;
// Generate an auth value for the imported matching in strength the signing scheme
byte[] authVal = Substrate.RandomAuth(sigHashAlg);
// We need a storage key to use as a parent of the imported key.
// The following helper creates an RSA primary storage key.
TpmHandle hParent = Substrate.CreateRsaPrimary(tpm);
TssObject importedKey = ImportExternalRsaKey(tpm, hParent,
keySize, sigScheme,
externalRsaKey.Public, externalRsaKey.Private,
keyAttrs, authVal);
// Now we can load the newly imported key into the TPM, ...
TpmHandle hImportedKey = tpm.Load(hParent, importedKey.Private, importedKey.Public);
// ... let the TSS know the auth value associated with this handle, ...
hImportedKey.SetAuth(authVal);
// ... and use it to sign something to check if import was OK
TpmHash toSign = TpmHash.FromRandom(sigHashAlg);
ISignatureUnion sig = tpm.Sign(hImportedKey, toSign, null, new TkHashcheck());
// Verify that the signature is correct using the public part of the imported key
bool sigOk = importedKey.Public.VerifySignatureOverHash(toSign, sig);
testCtx.Assert("Signature.OK", sigOk);
// Cleanup
tpm.FlushContext(hImportedKey);
// The parent key handle can be flushed immediately after it was used in the Load() command
tpm.FlushContext(hParent);
// Imported private/public key pair (in the TssObject) can be stored on disk, in the cloud,
// etc. (no additional protection is necessary), and loaded into the TPM as above whenever
// the key is needed.
// Alternatively the key can be persisted in the TPM using the EvictControl() command
} // ExternalKeyImportSample
void LoadExternalFullRsaKeySample(Tpm2 tpm, TestContext testCtx)
{
var hashAlg = TpmAlgId.Sha256;
var inPub = new TpmPublic(hashAlg,
ObjectAttr.Decrypt | ObjectAttr.UserWithAuth | ObjectAttr.SensitiveDataOrigin,
null,
new RsaParms(new SymDefObject(), new SchemeOaep(hashAlg), 2048, 0),
new Tpm2bPublicKeyRsa());
// Create a software RSA key
var swKey = new AsymCryptoSystem(inPub);
// The crucial point in loading a software key is preparing the TPM-formatted private part of the key
Sensitive sens = swKey.GetSensitive();
TpmHandle extKey = tpm.LoadExternal(sens, swKey.GetPublicParms(), TpmRh.Null);
//
// Make sure that the key was loaded correctly
//
// This particular label is used by the TPM while doing OAEP for its internal protocols
// (though in n general any label can be used).
byte[] label = RawRsa.GetLabel("OaepLabel");
byte[] origMsg = Substrate.RandomBytes(64);
// Encrypt using software key (the paublic part is used)
byte[] encMsg = swKey.EncryptOaep(origMsg, label);
testCtx.AssertNotEqual("SwEnc", origMsg, encMsg);
// Decrypt using the TPM (the private part is used)
byte[] decMsg = tpm.RsaDecrypt(extKey, encMsg, null, label);
testCtx.AssertEqual("CrossEncDec", origMsg, decMsg);
tpm.FlushContext(extKey);
}
/// <summary>
/// Create a new asymmetric key based on the parameters in keyParms. The resulting key data is returned in structures
/// suitable for incorporation in a TPMT_PUBLIC and TPMS_SENSITIVE
/// </summary>
/// <param name="keyParms"></param>
/// <param name="publicParms"></param>
/// <returns></returns>
internal static ISensitiveCompositeUnion CreateSensitiveComposite(TpmPublic keyParms, out IPublicIdUnion publicParms)
{
TpmAlgId keyAlgId = keyParms.type;
ISensitiveCompositeUnion newSens;
// Create the asymmetric key
if (keyAlgId != TpmAlgId.Rsa)
{
throw new Exception("Algorithm not supported");
}
var newKeyPair = new RawRsa((keyParms.parameters as RsaParms).keyBits);
// Put the key bits into the required structure envelopes
newSens = new Tpm2bPrivateKeyRsa(newKeyPair.Private);
publicParms = new Tpm2bPublicKeyRsa(newKeyPair.Public);
return newSens;
}
