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- Hacker News
- Let's hope this doesn't get picked up by the (corporate) masses... the last thing I want is my browser offering personal TLS certificates to every server I visit as some kind of identity verification or fingerprint/tracking.
It's bad enough that ssh does this by default with all your keys.
- Client TLS is rather unusable on the Internet by a typical random end user visiting a random public site, so that should at least keep the specific scenario you describe at bay.by altairprime
- This is most probably where it's going in less than a year. The recent campaign "Safer with Google" in Chrome hints to this.by zx8080
- I wonder, at what point will it be cheaper to kidnap and ransom those remote attestation engineers' families for key material than to work around those schemes with technical measures. Keeping in mind that people set up bot farms with physical phones just for attestation keys, it seems like tightening it all too much will just shift the balance towards the $5 wrench approach...
- Joke's on them, I don't have the key either.
- Oh great, a new fresh hell against users, keeping them from being able to see the world or understand computing. Fantastic.
The War Against General Purpose Computing ticks on.
- I wish the author provided some latency numbers for this. One issue with tpms is that they are slow relative to performing the same operation on a modern CPU.by psanford
- Thats the “what it costs” section? Im a bit impressed if they are down to ~3ms per handshake. When I last looked at TPM signing (many years ago) it was more like single digit transactions per second.
That said, even 3ms TPM signatures are going to be for special cases or novelty. Plain old CPU tls will do about 1ms cpu time per request which will scale by cpu core count. One or two orders of magnitude more throughput per host.
by donavanm - Author here. There's a benchmark table further down the post, the numbers come from this repo if you want to run them yourself: https://github.com/bschaatsbergen/go-tpm-tls-bench
- I might be missing something: is this any conceptually different from using PKCS11 provider for TPM in OpenSSL?
Also, with real TPM, the key could be locked to a specific configuration register value, which makes less sense for VMs. “Quote” is mentioned and I guess author means that, but did not elaborate further.
by ivlad - > is this any conceptually different from using PKCS11 provider for TPM in OpenSSL?
PKCS11 doesn't allow you to attest that the key is resident in the PKCS11 provider, which as you say, the author alludes to, but doesn't cover.
> with real TPM, the key could be locked to a specific configuration register value, which makes less sense for VMs.
A vTPM is as real as a physical TPM chip.
The question is which TPM endorsement certificate CAs you are willing to trust.
For some that might the manufacturer of TPM chips, for others it might be their VM provider. (For some, none: for some both!)
Trusting their VM provider isn't so crazy if the VM provider is able to influence the guest code anyway.
by flippingheck - Nothing new here, attested TLS was being discussed in IETF for quiet sometime right?
https://datatracker.ietf.org/doc/draft-fossati-tls-attestati... https://www.youtube.com/watch?v=MF9AwkMJOlw
by ram_rattle - Exactly, you could do this also with the Microsoft Cryptographic Provider long time ago, which is the basic Provider called by the go-tpm library, when running under Windowsby madduci
- Attested TLS has had some rough patches lately which can be attributed to making big changes to a complex protocol.
It really better to separate the attestation, the check against policy and then the TLS stuff. Solve one problem at a time, sign that progress and move on.
by ted_dunning - That's right, I'm learning in public here. That draft is a different direction though, they change the handshake: new TLS extensions carry the evidence, and the far end appraises the platform during the connection.
What I'm doing changes nothing on the wire, the verifying side has no idea a TPM is involved. In RATS (https://www.rfc-editor.org/rfc/rfc9334.html) we prove a machine is sound by measuring it and appraising the evidence. But after attestation the usual thing is to hand the machine a short-lived identity saying it is attested, and when that machine then authenticates over mTLS to something like an HSM, the thing that gives that machine its identity is a private key in a file. That bothered me. What I want is to tie the key in the TPM to the evidence of the confidential VM at issuance time, and let that be the identity the machine carries afterwards. Working notes while implementing RFC 9334.
- Isn't this a well-discussed issue already, and not specific to TPM?
We faced a similar issue (we use OpenSSL). OpenSSL does have OPENSSL_secure_malloc() which prevents sensitive memory from being dumped. However, the problem is that not all paths use the secure allocator. For example, this issue: https://github.com/openssl/openssl/issues/27603
Not sure if this has changed in OpenSSL 4.x, but it is certainly something desirable.
- The link between attestation and the key is nicely made with TAS. TAS gives you a cert and Spiffe then requires a cert like that to give a SVID that you use as a certificate for mTLS.
This means that the root of trust threads through software (TAS) that verified that your attestation evidence matches the live policy. This works with no changes to Spiffe.
This doesn't really meet your requirements to keep the key out of memory since the resulting SVID lasts for several minutes in memory, but it does meet most people's needs.
by ted_dunning - Thanks for sharing Ted!
- This feels like a somewhat odd design choice - you have a TEE, most TEEs (outside TPMs) are fast so there's little overhead in pushing your signing through there, why bother with short-lived credentials instead of just attesting to private key material ownership and having that be what the SPIFFE cert is issued to? Bearer token SVIDs are an awful thing that we should be getting as far away from as possible.by mjg59
- For a company I work for I needed to ship a machine through unknown channels and have some confidence that it wasn't fiddled with.
my threat model was reasonably technical engineer swapping drives for some reason, or someone claiming that the machine is "different". (no nation state shit)
after the machine was imaged, it would connect to our central config server, get its hostname and exchange keys which would be embedded in the TPM.
once the machine is shipped and booted, it'll check in and sign a challenge. any kind of action on the central API could have a challenge. Each machine is attested at least once an hour.
I'm not sure how "secure" it all is, but it seems to work.
by KaiserPro - I helped design the attestation framework for https://docs.cloud.google.com/transfer-appliance/docs/4.0/re... - the goal was to ensure that the device you're about to copy a bunch of sensitive information onto is actually the device you were shipped and is running the expected software. This is definitely used in the real world.by mjg59
- Looks like speeds have picked up since I last looked at this, when a signature in TPM took 0.7s and no concurrent capacity.
https://blog.habets.se/2012/02/Benchmarking-TPM-backed-SSL.h...
https://blog.habets.se/2012/02/TPM-backed-SSL.html
Well, it's been over 14 years so I should hope so.
- Yeah, a typical TPM chip has much lower throughput than OP.
Not suitable for servers, since it's such an easy DoS vector.
by flippingheck - The benchmarks are from GCP, where the vTPM is implemented in the hypervisor rather than on something that's plausibly an 8051[1]. Doing this on actual client hardware is going to be a bunch slower.
[1] Typically ARM these days, but most system vendors aren't picking TPM vendors based on performance
by mjg59 - I suppose the value of this depends on your threat model.
The TPM will give you stronger assurance that a machine owns a key, but it's likely that a dedicated HSM would be much harder to extract the key material from.
TPM being inside the machine is a double edged sword. On one hand it makes attestation feasible, but on the other you now have the security black box inside the same physical domain as the machine that uses it. Risk of side channel extraction goes up dramatically when these systems coexist. It's a lot harder to instrument an HSM across the network.
by bob1029 - A dedicated HSM will give you stronger trust that the private key material can't be extracted, but there's no real way to bind an HSM to a specific client and that's a very easy thing to do in the vTPM case.by mjg59
- TPM is just a spec, it isn't necessarily a black box.
ARM TrustZone, for example, can run this OSS TPM: https://github.com/OP-TEE/optee_ftpm
I expect there are equivalents for Intel/AMD.
by flippingheck - Sounds interesting; too bad all we get is text made up by an LLM rather than any of the author's insights.by duk3luk3
- Author here. All of it is mine, the library (https://github.com/bschaatsbergen/go-tpm-tls) and the benchmarks (https://github.com/bschaatsbergen/go-tpm-tls-bench) and the working notes. English isn't my first language, so I edit a lot, and I can see how that comes out flat. I've been over it once more; hopefully it reads better now. Thanks for saying so rather than just closing the tab.
- Yeah I was interested for the first few paragraphs, then all of a sudden I get hit with two "genuinely"s and a
> That’s the third property, and it’s the one that decides this.
and I gave up at that point.
by abound