/// <summary>
/// Illustrates various cases of automatic authorization handling.
/// </summary>
static void AutomaticAuth(Tpm2 tpm)
{
TpmHandle primHandle = CreateRsaPrimaryKey(tpm);
TpmPublic keyPublic;
TpmHandle keyHandle = CreateSigningDecryptionKey(tpm, primHandle, out keyPublic);
byte[] message = Globs.GetRandomBytes(32);
IAsymSchemeUnion decScheme = new SchemeOaep(TpmAlgId.Sha1);
ISigSchemeUnion sigScheme = new SchemeRsassa(TpmAlgId.Sha1);
//
// TSS.Net implicitly creates an auth session to authorize keyHandle.
// It uses the auth value cached in the TpmHandle object.
//
byte[] encrypted = tpm.RsaEncrypt(keyHandle, message, decScheme, null);
Console.WriteLine("Automatic authorization of a decryption key.");
//
// An auth session is added automatically when TPM object is not in strict mode.
//
byte[] decrypted1 = tpm.RsaDecrypt(keyHandle, encrypted, decScheme, null);
byte[] nonceTpm;
Console.WriteLine("Session object construction.");
//
// If a session with specific properties is required, an AuthSession object
// can be built from the session handle returned by the TPM2_StartAuthSession
// command concatenated, if necessary, with session flags and unencrypted salt
// value (not used in this example).
//
AuthSession auditSess = tpm.StartAuthSession(
TpmRh.Null, // no salt
TpmRh.Null, // no bind object
Globs.GetRandomBytes(16), // nonceCaller
null, // no salt
TpmSe.Hmac, // session type
new SymDef(), // no encryption/decryption
TpmAlgId.Sha256, // authHash
out nonceTpm)
+ (SessionAttr.ContinueSession | SessionAttr.Audit);
/*
* Alternatively one of the StartAuthSessionEx helpers can be used). E.g.
*
* AuthSession auditSess = tpm.StartAuthSessionEx(TpmSe.Hmac, TpmAlgId.Sha256,
* SessionAttr.ContinueSession | SessionAttr.Audit);
*/
//
// TSS.Net specific call to verify TPM auditing correctness.
//
tpm._SetCommandAuditAlgorithm(TpmAlgId.Sha256);
Console.WriteLine("Automatic authorization using explicitly created session object.");
//
// Appropriate auth value is added automatically into the provided session.
//
// Note that the call to _Audit() is optional and is only used when one
// needs the TSS.Net framework to compute the audit digest on its own (e.g.
// when simulating the TPM functionality without access to an actual TPM).
//
byte[] decrypted2 = tpm[auditSess]._Audit()
.RsaDecrypt(keyHandle, encrypted, decScheme, null);
ISignatureUnion signature;
Attest attest;
//
// A session is added automatically to authorize usage of the permanent
// handle TpmRh.Endorsement.
//
// Note that if auth value of TpmRh.Endorsement is not empty, you need to
// explicitly assign it to the tpm.EndorsementAuth property of the given
// Tpm2 object.
//
attest = tpm.GetSessionAuditDigest(TpmRh.Endorsement, TpmRh.Null, auditSess,
null, new NullSigScheme(), out signature);
//
// But if the corresponding auth value stored in the Tpm2 object is invalid, ...
//
AuthValue endorsementAuth = tpm.EndorsementAuth;
tpm.EndorsementAuth = Globs.ByteArray(16, 0xde);
//
// ... the command will fail.
//
tpm._ExpectError(TpmRc.BadAuth)
.GetSessionAuditDigest(TpmRh.Endorsement, TpmRh.Null, auditSess,
null, new NullSigScheme(), out signature);
//
// Restore correct auth value.
//
tpm.EndorsementAuth = endorsementAuth;
//
// Verify that decryption worked correctly.
//
Debug.Assert(Globs.ArraysAreEqual(decrypted1, decrypted2));
//
// Verify that auditing worked correctly.
//
SessionAuditInfo info = (SessionAuditInfo)attest.attested;
Debug.Assert(Globs.ArraysAreEqual(info.sessionDigest, tpm._GetAuditHash().HashData));
Console.WriteLine("Auth value tracking by TSS.Net.");
//
// Change auth value of the decryption key.
//
TpmPrivate newKeyPrivate = tpm.ObjectChangeAuth(keyHandle, primHandle, AuthValue.FromRandom(16));
TpmHandle newKeyHandle = tpm.Load(primHandle, newKeyPrivate, keyPublic);
//
// Allow non-exclusive usage of the audit session.
//
auditSess.Attrs &= ~SessionAttr.AuditExclusive;
//
// Correct auth value (corresponding to newKeyHandle, and different from
// the one used for keyHandle) will be added to auditSess.
//
decrypted1 = tpm[auditSess]._Audit()
.RsaDecrypt(newKeyHandle, encrypted, decScheme, null);
Console.WriteLine("Automatic authorization with multiple sessions.");
//
// Now two sessions are auto-generated (for TpmRh.Endorsement and keyHandle).
//
attest = tpm.GetSessionAuditDigest(TpmRh.Endorsement, keyHandle, auditSess,
null, sigScheme, out signature);
//
// Verify that the previous command worked correctly.
//
bool sigOk = keyPublic.VerifySignatureOverData(Marshaller.GetTpmRepresentation(attest),
signature);
Debug.Assert(sigOk);
//
// In the following example the first session is generated based on session
// type indicator (Auth.Pw), and the second one is added automatically.
//
attest = tpm[Auth.Pw].GetSessionAuditDigest(TpmRh.Endorsement, keyHandle, auditSess,
null, sigScheme, out signature);
//
// Verify that the previous command worked correctly.
//
sigOk = keyPublic.VerifySignatureOverData(Marshaller.GetTpmRepresentation(attest),
signature);
Debug.Assert(sigOk);
//
// Release TPM resources that we do not need anymore.
//
tpm.FlushContext(newKeyHandle);
tpm.FlushContext(auditSess);
//
// The following example works correctly only when TPM resource management
// is not enabled (e.g. with TPM simulator, or when actual TPM is in raw mode).
//
if (!tpm._GetUnderlyingDevice().HasRM())
{
Console.WriteLine("Using session type indicators.");
//
// Deplete TPM's active session storage
//
List <AuthSession> landfill = new List <AuthSession>();
for (;;)
{
tpm._AllowErrors();
AuthSession s = tpm.StartAuthSessionEx(TpmSe.Hmac, TpmAlgId.Sha256,
SessionAttr.ContinueSession);
if (!tpm._LastCommandSucceeded())
{
break;
}
landfill.Add(s);
}
//
// Check if session type indicators are processed correctly
//
tpm[Auth.Hmac]._ExpectError(TpmRc.SessionMemory)
.RsaDecrypt(keyHandle, encrypted, new NullAsymScheme(), null);
//
// Password authorization protocol session uses a predefined handle value,
// so it must work even when there are no free session slots in the TPM.
//
tpm[Auth.Pw].RsaDecrypt(keyHandle, encrypted, new NullAsymScheme(), null);
//
// Check if default session type defined by the TPM device is processed correctly.
//
bool needHmac = tpm._GetUnderlyingDevice().NeedsHMAC;
tpm._GetUnderlyingDevice().NeedsHMAC = true;
tpm._ExpectError(TpmRc.SessionMemory)
.RsaDecrypt(keyHandle, encrypted, new NullAsymScheme(), null);
tpm[Auth.Default]._ExpectError(TpmRc.SessionMemory)
.RsaDecrypt(keyHandle, encrypted, new NullAsymScheme(), null);
tpm._GetUnderlyingDevice().NeedsHMAC = false;
tpm.RsaDecrypt(keyHandle, encrypted, new NullAsymScheme(), null);
tpm[Auth.Default].RsaDecrypt(keyHandle, encrypted, new NullAsymScheme(), null);
tpm._GetUnderlyingDevice().NeedsHMAC = needHmac;
landfill.ForEach(s => tpm.FlushContext(s));
}
//
// Release TPM resources.
//
tpm.FlushContext(keyHandle);
tpm.FlushContext(primHandle);
Console.WriteLine("Done.");
}
void TestAutomaticAuth(Tpm2 tpm, TestContext testCtx)
{
TpmHandle hPrim = Substrate.LoadRsaPrimary(tpm);
// Make an RSA encryption key.
var decScheme = new SchemeOaep(Substrate.Random(TpmCfg.HashAlgs));
var sigScheme = new SchemeRsassa(Substrate.Random(TpmCfg.HashAlgs));
ushort keyLength = Substrate.RandomRsaKeySize(decScheme.hashAlg);
var inPub = new TpmPublic(Substrate.Random(TpmCfg.HashAlgs),
ObjectAttr.Decrypt | ObjectAttr.Sign
| ObjectAttr.FixedParent | ObjectAttr.FixedTPM
| ObjectAttr.UserWithAuth | ObjectAttr.SensitiveDataOrigin,
null,
new RsaParms(new SymDefObject(), null, keyLength, 0),
new Tpm2bPublicKeyRsa());
TpmPublic keyPublic;
TpmPrivate keyPrivate = Substrate.Create(tpm, hPrim, inPub, out keyPublic);
TpmHandle keyHandle = null;
tpm._Behavior.Strict = true;
try
{
// No auth session is added automatically when TPM object is in strict mode.
tpm._ExpectError(TpmRc.AuthMissing)
.Load(hPrim, keyPrivate, keyPublic);
// Now explicitly request an auth session of appropriate type
keyHandle = tpm[Auth.Default].Load(hPrim, keyPrivate, keyPublic);
}
finally
{
tpm._Behavior.Strict = false;
}
byte[] message = Substrate.RandBytes(1, TpmHelper.MaxOaepMsgSize(keyLength, decScheme.hashAlg));
byte[] encrypted = tpm.RsaEncrypt(keyHandle, message, decScheme, null);
// An auth session is added automatically when TPM object is not in strict mode.
byte[] decrypted1 = tpm.RsaDecrypt(keyHandle, encrypted, decScheme, null);
TpmAlgId auditHashAlg = Substrate.Random(TpmCfg.HashAlgs);
byte[] nonceTpm;
// AuthSession object can be built from session handle concatenated, if necessary,
// with session flags and unencrypted salt value (not used in this example).
AuthSession auditSess = tpm.StartAuthSession(
TpmRh.Null, // no salt
TpmRh.Null, // no bind object
Substrate.RandomNonce(auditHashAlg), // nonceCaller
null, // no salt
TpmSe.Hmac, // session type
new SymDef(), // no encryption/decryption
auditHashAlg, // authHash
out nonceTpm)
+ (SessionAttr.ContinueSession | SessionAttr.Audit);
/*
* Alternatively one of the StartAuthSessionEx helpers can be used)
* AuthSession auditSess = tpm.StartAuthSessionEx(TpmSe.Hmac, auditHashAlg, null,
* SessionAttr.ContinueSession | SessionAttr.Audit);
*/
// TSS-specific call to verify TPM auditing correctness.
tpm._SetCommandAuditAlgorithm(auditHashAlg);
// Appropriate auth value is added automatically into the provided session
byte[] decrypted2 = tpm[auditSess]._Audit()
.RsaDecrypt(keyHandle, encrypted, decScheme, null);
ISignatureUnion sig;
Attest attest;
// A session is added automatically to authorize TpmRh.Endorsement usage.
attest = tpm.GetSessionAuditDigest(TpmRh.Endorsement, TpmRh.Null, auditSess,
null, new NullSigScheme(), out sig);
// But if the corresponding auth value stored in the Tpm2 object is invalid, ...
AuthValue endorsementAuth = tpm.EndorsementAuth;
tpm.EndorsementAuth = Globs.ByteArray(16, 0xde);
// ... the command will fail
tpm._ExpectError(TpmRc.BadAuth)
.GetSessionAuditDigest(TpmRh.Endorsement, TpmRh.Null, auditSess,
null, new NullSigScheme(), out sig);
// Restore correct auth value.
tpm.EndorsementAuth = endorsementAuth;
// Verify that both decryption and auditing worked correctly.
SessionAuditInfo info = (SessionAuditInfo)attest.attested;
byte[] auditDigest = tpm._GetAuditHash();
testCtx.AssertEqual("AuditSessionDigest", info.sessionDigest, auditDigest);
testCtx.AssertEqual("Decryption", decrypted1, decrypted2);
// Change auth value of the decryption key.
TpmPrivate newKeyPrivate = tpm.ObjectChangeAuth(keyHandle, hPrim,
Substrate.RandomAuth(keyPublic.nameAlg));
TpmHandle newKeyHandle = tpm.Load(hPrim, newKeyPrivate, keyPublic);
auditSess.Attrs &= ~SessionAttr.AuditExclusive;
// Correct auth value (corresponding to newKeyHandle, and different from
// the one used for keyHandle) will be added to auditSess.
decrypted1 = tpm[auditSess]._Audit().RsaDecrypt(newKeyHandle, encrypted, decScheme, null);
// And now two sessions are auto-generated (for TpmRh.Endorsement and keyHandle).
attest = tpm.GetSessionAuditDigest(TpmRh.Endorsement, keyHandle, auditSess,
null, sigScheme, out sig);
bool sigOk = keyPublic.VerifySignatureOverData(
Marshaller.GetTpmRepresentation(attest), sig);
testCtx.Assert("AuditSessionSignatute.1", sigOk);
// Here the first session is generated based on session type indicator
// (Auth.Pw), and the second one is added automatically.
attest = tpm[Auth.Pw].GetSessionAuditDigest(TpmRh.Endorsement, keyHandle, auditSess,
null, sigScheme, out sig);
// Verify that auditing worked correctly.
sigOk = keyPublic.VerifySignatureOverData(
Marshaller.GetTpmRepresentation(attest), sig);
testCtx.Assert("AuditSessionSignatute.2", sigOk);
tpm.FlushContext(newKeyHandle);
tpm.FlushContext(auditSess);
if (!TestCfg.HasTRM)
{
// Deplete TPM's active session storage
List <AuthSession> landfill = new List <AuthSession>();
for (;;)
{
tpm._AllowErrors();
AuthSession s = tpm.StartAuthSessionEx(TpmSe.Hmac, Substrate.Random(TpmCfg.HashAlgs),
SessionAttr.ContinueSession);
if (!tpm._LastCommandSucceeded())
{
break;
}
landfill.Add(s);
}
// Check if session type indicators are processed correctly
tpm[Auth.Hmac]._ExpectError(TpmRc.SessionMemory)
.RsaDecrypt(keyHandle, encrypted, null, null);
tpm[Auth.Pw].RsaDecrypt(keyHandle, encrypted, null, null);
// Check if default session type defined by the TPM device is processed correctly
bool needHmac = tpm._GetUnderlyingDevice().NeedsHMAC;
tpm._GetUnderlyingDevice().NeedsHMAC = true;
tpm._ExpectError(TpmRc.SessionMemory)
.RsaDecrypt(keyHandle, encrypted, null, null);
tpm[Auth.Default]._ExpectError(TpmRc.SessionMemory)
.RsaDecrypt(keyHandle, encrypted, null, null);
tpm._GetUnderlyingDevice().NeedsHMAC = false;
tpm.RsaDecrypt(keyHandle, encrypted, null, null);
tpm[Auth.Default].RsaDecrypt(keyHandle, encrypted, null, null);
tpm._GetUnderlyingDevice().NeedsHMAC = needHmac;
landfill.ForEach(s => tpm.FlushContext(s));
}
tpm.FlushContext(keyHandle);
} // TestAutomaticAuth