wan24-Crypto-TPM
2.10.0
dotnet add package wan24-Crypto-TPM --version 2.10.0
NuGet\Install-Package wan24-Crypto-TPM -Version 2.10.0
<PackageReference Include="wan24-Crypto-TPM" Version="2.10.0" />
paket add wan24-Crypto-TPM --version 2.10.0
#r "nuget: wan24-Crypto-TPM, 2.10.0"
// Install wan24-Crypto-TPM as a Cake Addin #addin nuget:?package=wan24-Crypto-TPM&version=2.10.0 // Install wan24-Crypto-TPM as a Cake Tool #tool nuget:?package=wan24-Crypto-TPM&version=2.10.0
wan24-Crypto-TPM
WARNING: The code has not been tested with a real TPM running on Linux yet. I'd appreciate if someone would give me some feedback, if it worked for them. Anyway the tests use the Microsoft TPM simulator and did run successfully (and also with a real TPM device on Windows 11).
This library contains some helpers for easy TPM(2) usage. It does way not implement everything that a TPM offers - these are the selected features, which include the TPM into your security model:
- Determine if TPM2 can be accessed
- Determine the max. supported digest (size)
- Random number generation (
TpmRng
) - HMAC-SHA-1/256/384/512 (
Tpm2Helper
andMacTpmHmacSha*Algorithm
) TpmSymmetricKeySuite
which implementsISymmetricKeySuite
TpmSecuredValue
which works likeSecureValue
TpmSharedSecret
for usage with a remote key storageTpmValueProtection
to extendValueProtection
As you can see, the number of features is quiet clear.
This library extends the wan24-Crypto
library with these algorithms:
Algorithm | ID | Name |
---|---|---|
MAC | ||
TPM HMAC-SHA-1 | 7 | TPMHMAC-SHA-1 |
TPM HMAC-SHA-256 | 8 | TPMHMAC-SHA-256 |
TPM HMAC-SHA-384 | 9 | TPMHMAC-SHA-384 |
TPM HMAC-SHA-512 | 10 | TPMHMAC-SHA-512 |
CAUTION: TPM secured information won't be usable anymore, if the TPM (or even the TPM owner) changes!
The goal of this library is to make TPM usable for everyone in a simple way,
without having to fight with a firmware and complex/missing documentation.
It's an ideal extension to the existing wan24-Crypto
infrastructure.
NOTE: There are no provisioning functionaliies implemented in this library. A TPM which is going to be used needs to be provisioned manually or from the host OS (Windows f.e. does provision a TPM automatically).
How to get it
This library is available as NuGet package.
Usage
In case you don't use the wan24-Core
bootstrapper logic, you need to
initialize the TPM2 extension first, before you can use it:
wan24.Crypto.TPM.Bootstrap.Boot();
This will register the algorithms to the wan24-Crypto
library.
NOTE: All algorithms will be registered, no matter if there's even a TPM available or not, or if the algorithm is supported by an available TPM. This is because the TPM options support configuring a simulator or to choose between multiple available TPMs. So the bootstrapper can't really know which algorithms are going to be available (or used).
In case you work with dependency injection (DI), you may want to add some services:
builder.Services.AddWan24CryptoTpm();
This will register transient Tpm2Options
(using Tpm2Helper.DefaultOptions
)
and Tpm2
(using Tpm2Helper.CreateEngine
) service objects.
JSON configuration
You could implement a JSON configuration file using the AppConfig
logic from
wan24-Core
, and the TpmCryptoAppConfig
. There it's possible to define
disabled algorithms, which makes it possible to react to an unwanted algorithm
very fast, at any time and without having to update your app, for example. If
you use an AppConfig
, it could look like this:
public class YourAppConfig : AppConfig
{
public YourAppConfig() : base() { }
[AppConfig(AfterBootstrap = true, Priority = 20)]
public CryptoAppConfig? Crypto { get; set; }
[AppConfig(AfterBootstrap = true, Priority = 10)]
public TpmCryptoAppConfig? Tpm { get; set; }
}
await AppConfig.LoadAsync<YourAppConfig>();
NOTE: A TpmCryptoAppConfig
should be applied before a CryptoAppConfig
.
For this reason the example defines a priority in the AppConfigAttribute
.
In the config.json
in your app root folder:
{
"Tpm":{
...
}
}
Anyway, you could also place and load a TpmCryptoAppConfig
in any
configuration which supports using that custom type.
Tpm2Engine
fixes multithreading bugs
Using a Tpm2
instance for each thread still has multithreading problems in
the MS.TSS .NET library, that's why a Tpm2Engine
should be used in
multithreading environments. It ensures that
- only one
Tpm2
instance is being used at a time - only one thread can use the
Tpm2
instance at a time
Example:
// Creating a Tpm2Engine uses static thread synchronization (a Tpm2Engine instance should be singleton)
using Tpm2Engine engine = Tmp2Engine.Create();
// Using per-engine thread synchronization (optional, to use one Tpm2Engine instance from multiple threads)
using SemaphoreSyncContext ssc = engine.Sync;
// Now you can perform a TPM operation using the engine.TPM property, which hosts the Tpm2 instance
NOTE: This is only required unless the multithreading bugs in the MS.TSS
.NET library has been fixed by its vendor. In theory it should be possible to
use a Tpm2
instance per thread without static thread locking (while
multithreaded access to a Tpm2
instance still requires thread
synchronization).
In case you're using Tpm2Helper.DefaultEngine
, the Tpm2Engine
usage is
slightly different:
// Creating a Tpm2Engine uses static thread synchronization (a Tpm2Engine instance should be singleton)
using Tpm2Engine engine = new();// The empty constructor will use the Tpm2Helper.DefaultEngine and Tpm2Helper.DefaultEngineSync
// Using per-engine thread synchronization
using SemaphoreSyncContext ssc = engine.Sync;
// Now you can perform a TPM operation using the engine.TPM property, which hosts the Tpm2 instance
Implemented types support using a Tpm2Engine
also, which will then not be
disposed, but used for synchronizing the TPM access.
TPM2 options
In the Tpm2Options
you can define how to connect to the TPM. You may also
specify
- a resource handle (currently used for finalizing a HMAC)
- an algorithm (currently used for creating a HMAC)
- a tagged object (which will be cloned, if it implements
ICloneable
, and theGetCopy
method of theTpm2Options
instance has been called)
Using the With*
methods you can configure options fluent.
Determine if TPM2 can be accessed
bool canAccessTpm2 = Tpm2Helper.IsAvailable();
Because on a Linux system some file IO operations may run, there's an
IsAvailableAsync
method, too.
Tpm2
instance creation
using Tpm2 engine = Tpm2Helper.CreateEngine();
The Tpm2
instance is a connected TPM2 TSS, which allows to do whatever the
TSS offers. By giving Tpm2Options
to the CreateEngine
method, you can
define which TPM to use, and optional set an Initializer
delegate, which may
bring the TPM into the desired state, before running any other operation.
The CreateEngine
method is being called internal, whenever you use a TPM
functionality without giving an existing Tpm2
instance to the called method.
And if you didn't specify the Tpm2Options
, the Tpm2Helper.DefaultOptions
will be used, which you may preset, if required.
The TryCreateEngine
does the same as CreateEngine
, but won't throw on
error.
Maximum supported digest (size)
int maxDigestSize = Tpm2Helper.GetMaxDigestSize();// Size in byte
TpmAlgId maxDigest = Tpm2Helper.GetDigestAlgorithm(maxDigestSize);
The max. supported digest size limits the output of the random number generator, and it also defines the possible digest algorithms.
NOTE: TpmRng
doesn't limit the random number count being generated in
any way.
Random number generator
CAUTION: The example code is actually a negative example - see "Best practices" for a better solution suggestion!
RND.Generator = new TpmRng();// If not used as singleton, an instance should be disposed!
The TpmRng
implements the IRng
interface, which allows to use the TPM as
RNG for wan24-Crypto
. Internal it uses the Tpm2Helper.CreateRandomData
helper method, which is restricted to the TPMs random number output length,
while the RNG implementation doesn't restrict the length of the generated
random data.
HMAC-SHA-1/256/384/512
byte[] hmac = Tpm2Helper.Hmac(anyAuthMessage);
NOTE: The owner resource handle will be used per default.
Using the Tpm2Helper.Hmac
method you can create a HMAC-SHA-1/256/384/512
using the TPM. These HMACs can only be re-created using the same TPM.
Specifying an additional MAC key is optional.
NOTE: Not every TPM implements all algorithms. HMAC-SHA-256 seems to be
implemented by most TPMs. If you don't specify an algorithm to the Hmac
method, it'll determine and use the maximum supported algorithm.
CAUTION: If you change your TPM hardware, you won't be able to re-create a HMAC! This also applies even only the TPM owner changes.
You can also use the wan24-Crypto
registered HMAC algorithms during
encryption, for example. Then cipher data couldn't be decrypted on any other
computer than the one that encrypted it.
TIP: If you use a TPM HMAC of your encryption password, you can ensure that the cipher data can only be decrypted from the same computer that was used to encrypt it!
There are also TpmHmac*
extension methods for a byte[]
and
(ReadOnly)Span<byte>
.
TPM symmetric key suite
using TpmSymmetricKeySuite tpmAuth = new(key);
The TpmSymmetricKeySuite
works as the SymmetricKeySuite
, but uses a TPM
HMAC for calculating the final key (and identifier, if any).
TPM secured value
The TpmSecuredValue
works as SecureValue
and protects a value using the
TPM.
If you'd like TPM only if available, you can set the constructor parameter
value of requireTpm
to false
. If TPM is not available, the constructor
won't throw, and TpmSecuredValue
will just work as SecureValue
as a
fallback solution.
En-/decrypting a private key suite
Using the TpmEncrypt
extension method you can encrypt a PrivateKeySuite
using a TPM flavored key. With Tpm2Helper.DecryptPrivateKeySuite
you can
decrypt it.
CAUTION: If you change your TPM hardware, there's no way to decrypt the private key suite anymore! The cipher data can only be decrypted using the same TPM hardware that was used for encryption. This also applies even only the TPM owner changes.
En-/decrypting a key ring
Using the TpmEncrypt
extension method you can encrypt a KeyRing
using a
TPM flavored key. With Tpm2Helper.DecryptKeyRing
you can decrypt it.
CAUTION: If you change your TPM hardware, there's no way to decrypt the key ring anymore! The cipher data can only be decrypted using the same TPM hardware that was used for encryption. This also applies even only the TPM owner changes.
TPM shared secret
The TpmSharedSecret
is a helper for deriving a TPM secured key from a remote
key storage.
NOTE: The following examples assume that your remote key storage requires sending a secret for receiving a secret. This may be different per each remote key storage.
Example how to initialize a new secret:
using Tpm2 engine = Tpm2Helper.CreateEngine();
byte[] token = RND.GetBytes(Tpm2Helper.GetMaxDigestLength(engine)),
remoteSecret = RND.GetBytes(token.Length);
// Store the token somewhere for restoring the secret later
using TpmSharedSecret tpmSecret = new(token, engine: engine);
tpmSecret.ProtectRemoteSecret(remoteSecret);
// Send tpmSecret.Secret.Array and remoteSecret to the remote key storage
byte[] secret = tpmSecret + remoteSecret;
CAUTION: NEVER store remoteSecret
persistent outside of the remote
key storage! NEVER store tpmSecret.Secret.Array
anywhere!
tpmSecret.Secret.Array
is used to authenticate for receiving the value of
remoteSecret
from the remote key storage later.
NOTE: token
may be stored plain, maybe protected using the OS
capabilities (like the file system ACL, f.e.).
Example how to restore a previously initialized secret:
// Load the token from where it was saved during secret initialization
using TpmSharedSecret tpmSecret = new(token);
// Send tpmSecret.Secret.Array to the remote key storage and receive remoteSecret
byte[] secret = tpmSecret + remoteSecret;
The TpmSharedSecret
also supports including an additional secret (for user
authentication f.e.).
TPM value protection
The TpmValueProtection
uses the TPM for protecting a value as
ValueProtection
does without the TPM. For this the scope keys will be used
as value for a TPM HMAC, which will then be the final key being used for the
value encryption (the max. TPM supported HMAC algorithm will be used).
NOTE: The TpmValueProtection
uses the scope keys from ValueProtection
and uses the default TPM state for creating the HMAC. That means in particular
you'll still have to ensure a restorable user scope key, while you don't have
to take care the system scope key anymore.
You may replace the ValueProtection
protect/unprotect handlers:
TpmValueProtection.Enable();
NOTE: The TpmValueProtection
protect/unprotect handlers will connect to
the TPM for every call, which is an overhead and may impact the performance of
your application. If you don't want that, you may simply replace the
ValueProtection
user/system scope keys with TPM HMACs, probably including an
user secret for the user scope key.
Or you can use both, the ValueProtection
and the TpmValueProtection
, as it
is suitable for your application, separately.
Extension methods
The TpmExtensions
class exports some extension methods to make life more
easy, when working with TPM types and wan24-Crypto
. There are also
extensions for the PrivateKeySuite
, byte[]
and (ReadOnly)Span<byte>
(TPM HMAC creation). Using the CryptoOptions.WithTpmHmac
extension method,
you can set the max. supported TPM HMAC algorithm for any crypto application
which requires to compute a MAC.
Using a singleton TPM2 connection
By setting a Tpm2
instance to the Tpm2Helper.DefaultEngine
property, you
can specify a singleton connection to use from Tpm2Helper
methods. Use the
Tmp2Helper.DefaultEngineSync
to synchronize multithreaded connection usage:
// Set a singleton default TPM engine
Tpm2Helper.DefaultEngine = Tpm2Helper.CreateEngine();
// Synchronize the default TPM engine access before performing any Tpm2Helper operation
using SemaphoreSyncContext ssc = Tpm2Helper.DefaultEngineSync;
// Now you can perform any Tpm2Helper operation in a multithreaded environment using the singleton Tpm2Helper.DefaultEngine
The Tpm2Helper.DefaultEngine
value will be set to the engine
parameter of
Tpm2Helper
methods, if no value was given.
Why not support TPM PKI/signing/sealing/etc.?
If you followed the TPM development process until today you know that TPM2 is
fully incompatible with TPM1. I try to concentrate on the absolute minimum
that TPM offers, to stay (hopefully) compatible with TPM3 (or any future TPM
version). With the HMAC function you should have everything that is required
at minimum, for implementing everything else using wan24-Crypto
(which
offers way more functionality than TPM does). The ExpandedKey
of a
TpmSymmetricKeySuite
can be used for any encryption, and it's bound to the
available TPM, so you could encrypt a PrivateKeySuite
, for example, which
can then only be decrypted using the same TPM. And you're not bound to the TPM
implemented algorithms, as you have the free choice to use any wan24-Crypto
implemented cryptographic algorithm, and optional combine them with the
provided TPM functionality.
To sum it up - the reasons for not using all of the TPM capabilities:
- TPM doesn't implement the cryptographic algorithms that you need to use
- The TPM processing speed is decreased because of KDF usage in places where you don't want (need) to use KDF (at all)
- Future security developments require new TPM hardware, which will mess up your PKI
- TPM is way not the answer to all crypto related questions
- TPMx may fully break TPM2 key capabilities (again), while the implemented
features of
wan24-Crypto-TPM
may still be supported ('cause they're the absolute basics, which should be valid for at last the next decade from now)
There are many good reasons to use only the absolute basics of the offered TPM features, and only a few applications which are really enriched by the TPM, which is usually being used in normal devices.
Someone might argue that TPM can encrypt/decrypt (seal/unseal) data
independent from the OS and other hardware - yes, that's true. If AES-128 does
still fit your security policy in 2023+, you'd be fine with it (use Tpm2
).
But remember that the in-TPM en-/decryption is only suitable for small blobs!
This in combination limits the application in a way which is not acceptable
for the most use cases for cryptography: If you want to process larger blobs,
you have to DIY. If you need AES-256 (or any other algorithm than the TPM
implemented ones), you have to DIY. Instead of using the TPM lockout, DIY and
use KDF in addition. That's enough DIY to skip implementing support for the
TPM offered functionality into wan24-Crypto-TPM
and sticking to the TPMs
HMAC only, which is enough already (and not to forget the RNG also). Brute
Force will always stay possible, no matter if you use TPM or not - remember
that.
However, if you need all the TPM functionality (if your boss or a customer is
obsessed with TPM and no technical argument seems to count anymore - I know
something like that...), you're free to use Tpm2Helper.CreateEngine
and work
with the Tpm2
object directly and without any limit.
From my sight there's only one reason for sticking to the TPM implemented functionality: Private keys will be used for crypto/signature witin the TPM only, which allows protecting/authenticating sensitive information within an isolated processor, which runs independent from the rest of the system. But since the rest of the system controls the TPM, it's nothing more than a piece of hardware which can be used to identify a device. Remember that there's still software (the TSS and the firmware), which is required to be implemented, and is a point of failure for the TPM offered security stack. Once that software was attacked with success, your software has been broken, too. So even the identification of a device using TPM isn't 100% trustable.
Supported platforms
All platforms which support TPM should be supported by this library. Anyway, Apple devices often don't contain a TPM, but a T2 (which is similar to TPM) instead (which may be called T8012, too).
I've successfully run the tests on a Windows 11 computer only so far, since at the moment I don't own a Linux device with a TPM. But Linux supports TPM, and the underlaying TSS.MSR .NET library supports Linux, finally.
So the supported platform list may be:
- Windows (10+)
- Linux
- (MAC OSX)
There seems to be no .NET library for Apples T2 chip, and I'm not going to implement one. You could use the MAC OSX API for the T2 chip directly by using interop, but however, since HMAC seems not to be supported, I'd use a T2 as a better HWRNG only.
For Apple iOS (and others != OSX) there is a "Security Enclave", which is a SoC like TPM - but also without HMAC support, so it can be seen as a better HWRNG, too.
On an Android device you'd use the KeyChain or TEE API usually, but there could also be a TPM being supported. However, it's not supported by the TSS.MSR, so this library can't offer support, too.
To sum it up: Forget about Apple and Android, and concentrate on Windows and Linux, if you'd like to use this TPM library.
Best practice
TpmRng
usage
Random numbers are security critical, and it may be a bad idea to rely on one
entropy source or RNG only. For this I suggest to use the TpmRng
together
with other RNGs, and combine their generated random numbers using a XorRng
.
TPM encrypted PrivateKeySuite
When your app requires a TPM protected private key suite, you can create one with these steps:
- Create a
PrivateKeySuite
- Encrypt the
PrivateKeySuite
using theTpmEncrypt
extension method - Store the cipher data in a file
- Dispose the
PrivateKeySuite
when not in use anymore!
To load it when your app starts again:
- Decrypt the
PrivateKeySuite
cipher data from the file usingTpm2Helper.DecryptPrivateKeySuite
- Dispose the
PrivateKeySuite
when not in use anymore!
Persistent secret storage
Different OS offer different secret storage solutions - but none of them seem to offer a real security benefit. There's only one thing, which could enhance security (really): Storing a part of a secret at another system.
To make this process combinable with TPM, there's the TpmSharedSecret
helper class, which makes it possible to restore an (user) secret using a TPM
bound token, which may be stored in plain on the processing system, but
requires using a remote key storage to provide a partial key for a TPM
processed token value, which acts as a shared secret.
When storing a mashine scope secret, it ensures that
- the ciphered data on that mashine can be remote-deleted by simply deleting the remote stored secret
- someone which could access any key part (or both), but isn't able to access the TPM, can't get to the final key
When storing an user scope secret, it ensures in addition that
- even when having both key parts and access to the TPM, a dictionary or Brute Force attack on the user password isn't practicable, when the user password is secure (has been KDF processed)
These benefits apply to both sides: The local system, and the remote key storage. By the way the remote key storage should store the provided secret encrypted using the shared secret, and never store the shared secret anywhere.
To get a final key
- the plain stored token must be available (1st part of the key)
- access to the TPM must be available (for computing the shared secret)
- the remote storage must reply the 2nd part of the key for the provided shared secret
- another TPM access must be possible to combine both key parts
An attacker can't use the plain stored token (1st key part) alone. He even can't request the 2nd key part from the remote key storage, if the TPM can't be accessed. Also the 2nd key part alone doesn't offer any success for an attacker, if the TPM can't be accessed, too - and even when having both key parts, the TPM access is a required component to get to the final key. To break the security, an attacker requires both key parts and having access to the TPM. This applies to a mashine scope secret.
For an user scope secret, an attacker would then still need the user password.
To secure the user password, you should pre-process it using KDF before you
use it as the key
parameter in the TpmSharedSecret
constructor. This I'd
call an almost perfect solution in 2023 then.
Anyway, there are some pitfalls with that solution: IF
- the TPM (owner) changed, or the TPM is broken, then ciphered data is lost
- there is no connection to the remote key storage possible, ciphered data can't be accessed unless the connection problem was solved
- the remote stored key part got lost, then ciphered data is lost, too
It's important to have that in mind and implement emergency solutions for such (worst case) scenarios to avoid a data loss.
Product | Versions Compatible and additional computed target framework versions. |
---|---|
.NET | net8.0 is compatible. net8.0-android was computed. net8.0-browser was computed. net8.0-ios was computed. net8.0-maccatalyst was computed. net8.0-macos was computed. net8.0-tvos was computed. net8.0-windows was computed. |
-
net8.0
- Microsoft.TSS (>= 2.1.1)
- ObjectValidation (>= 2.8.0)
- Stream-Serializer-Extensions (>= 3.11.0)
- wan24-Core (>= 2.38.0)
- wan24-Crypto (>= 2.19.0)
NuGet packages
This package is not used by any NuGet packages.
GitHub repositories
This package is not used by any popular GitHub repositories.
Version | Downloads | Last updated | |
---|---|---|---|
2.10.0 | 76 | 9/21/2024 | |
2.9.0 | 82 | 9/9/2024 | |
2.8.0 | 121 | 8/16/2024 | |
2.7.1 | 91 | 7/13/2024 | |
2.7.0 | 104 | 7/6/2024 | |
2.6.0 | 97 | 6/22/2024 | |
2.5.0 | 97 | 5/20/2024 | |
2.4.0 | 133 | 3/9/2024 | |
2.3.0 | 126 | 3/2/2024 | |
2.2.0 | 117 | 2/24/2024 | |
2.1.1 | 124 | 2/17/2024 | |
2.1.0 | 118 | 2/11/2024 | |
2.0.0 | 98 | 1/20/2024 | |
1.1.0 | 141 | 11/27/2023 | |
1.0.1 | 127 | 11/11/2023 | |
1.0.0 | 118 | 11/1/2023 |