Thread

Apple Reference Image: A New Approach for Verified Photography

539 points · 352 comments · imwally

tgsovlerkhgsel · 1789535685 · focus · HN ↗
This is really clever from Apple. The journalist use case is just the PR story. This will be really useful for identity verification and insurance apps, and has the potential to shift from "you need a smartphone to be able to live normally" to "you need an iPhone to be able to live normally".
There are already plenty of insurances that require you to submit claims through a smartphone app that tries to essentially do this by capturing sensor metadata etc. - those don't need to be nation-state resilient, just Joe the Crackhead Insurance Scammer resilient, so this works. Likewise, more and more things online require identity verification (either officially or disguised as age verification).
Edit: And while "a nation state actor can spoof this" is a problem for the journalism use case, the insurance/ID verification use cases are perfectly fine with anything that raises the bar but could be bypassed with enough effort. Also, the journalism use case suffers from the same fundamental issue all of these use cases suffer from: People will "verify" the picture by looking at the repost of a screenshot of the verification UI, not by verifying the original themselves.
1. alwillis · 1789551144 · focus · HN ↗
  > This is really clever from Apple. The journalist use case is just the PR story. This will be really useful for identity verification and insurance apps, and has the potential to shift from "you need a smartphone to be able to live normally" to "you need an iPhone to be able to live normally".
  You have it all wrong.
  Apple Reference Image is not an id system; it's primarily a way to attest that the pixels recorded by the camera sensor have not been altered in any way; the pixels, metadata and timestamp are all cryptographically signed.
  There's no way to link a reference image to a person; it's also not possible to determine if a pair of images came from the same device.
  > And while "a nation state actor can spoof this" is a problem for the journalism use case
  This is incorrect:
  When the image sensor is first initialized in the factory, it creates a cryptographic signing identity, sharing only the public key with the factory. The SEP similarly creates a separately-attested signing identity. These identities are bound together into the device manifest, allowing us to later check whether a particular sensor and SEP are from the same device. The final signature on a reference image is a composite post-quantum signature combining RSA-3072 and ML-DSA-87. To our knowledge, Apple Reference Image is the only image provenance system that provides quantum-secure defenses.
  So… a nation-state can't really do anything here unless they acquire alien technology. If something crazy happens (solar flare or EMP?), a fraudulent reference image can be revoked.
  > Also, the journalism use case suffers from the same fundamental issue all of these use cases suffer from: People will "verify" the picture by looking at the repost of a screenshot of the verification UI, not by verifying the original themselves.
  I would imagine there will be a way to confirm an Apple Reference Image on the web. Pretty soon, 3rd parties will be able to verify the image themselves:
  Reference images can be viewed in the Photos app alongside the main image, like a digital negative, to visually compare the two assets and determine if any edits were made. APIs are available in iOS, iPadOS, and macOS 27 for third-party apps to enable viewing of these reference images.
  1. monocasa · 1789561959 · focus · HN ↗
    Nation states almost certainly have the ability to extract the private keys out of an image sensor and SEP. Outside of superpowers even if you're willing to do it destructively.
    They can then sign their own fraudulent images.
    autoexec · 1789576782 · focus · HN ↗
    The NSA has probably already forced Apple to hand the keys over to them.
    propaganja · 1789581170 · focus · HN ↗
    Apple would be legally restricted from disclosing any government compromises, while still claiming their systems are secure and operating as intended in general.
    We already know it's happening right now, and they know we know, but we can't do shit about it.
    alwillis · 1789598242 · focus · HN ↗
    > Apple would be legally restricted from disclosing any government compromises, while still claiming their systems are secure and operating as intended in general.
    I'm aware. The point is they can't give the NSA something they don't have. The photo sensor generates its own ECDSA P-256 signing key pair and never releases the private half.
    Every device has a unique key pair and the private key is unavailable… there's not a way to give the NSA that would help them. The system is setup so that the image data, meta data, etc can't be accessed by anyone including Apple.
    microtonal · 1789629463 · focus · HN ↗
    I believe them, but the process is hard to check. How do we verify that they don’t have the sensor burn in a private key generated by them?
    (Similar to how many PGP hardware keys allow generating a private key on-device or writing your own provided key.)
    alwillis · 1789609023 · focus · HN ↗
    Here's a flow chart; tell us at what point there's something Apple can be compelled by a 3-letter organization to produce: <a href="https://news.ycombinator.com/item?id=49735284">https://news.ycombinator.com/item?id=49735284
    microtonal · 1789631346 · focus · HN ↗
    I think the chart exactly shows the weakness that some people have pointed out. Apple's PCC servers at some point in time know the signing identity for a photo and Apple's generated replacement signature. The relevant steps from your chart:
    - verifies each link and its certificate chain, sensor signature over pixels, SEP signature, device manifest signature
    - PCC Submits the commitment (the JPEG hash) to Apple's signing service.
    So, at some point in time, Apple's servers have both the original certificate chain and the new replacement signature. If this is recorded, Apple can deanonimize photos and check whether two photos were from the same device/sensor.
    Apple's system protects against most state actors, except Apple and the US, unless you fully trust that their PCC is watertight.
    (Remember that Apple was part of PRISM and probably also its successor.)
    I don't think law enforcement needs it, because when sending/posting a picture, people leak so much metadata anyway.
    But people outside the US should certainly distrust these systems.
    alwillis · 1789581423 · focus · HN ↗
    > The NSA has probably already forced Apple to hand the keys over to them.
    Again, that's not how it works.
    There's no set of keys and certificates they could give to the NSA. Every iPhone 18 Pro and Pro Max has a unique set of cryptographic keys, most of which can't be accessed by Apple.
    The first thing that happens is when photo sensor is initialized at the factory, it creates its own ECDSA P-256 signing key pair; the private key is never disclosed. The public key is signed by the factory's certificate authority.
    This ain't X.509 where VeriSign's key pair is sitting in a HSM at their HQ and in theory could be forced to sign a fraudulent certificate or revoke someone's valid website certificate.
    microtonal · 1789629397 · focus · HN ↗
    They don’t need the signing keys though. Apple could roll out a separate version of sepOS to assist law enforcement that signs at they will.
    Also, while the unique device ID is supposed to be burned into fuses by the SE during production, it is kinda hard to prove for anyone that is not Apple that this indeed happens in the way they state.
    Personally I’m not a strong believer in such theories though. I think it’s more mundane and Apple helps law enforcement by having some weak defaults. Like how iMessage is end-to-end encrypted, but most chats are available to law enforcement because most people turn on iCloud Backups/Messages in iCloud and not ADP, resulting in chats only being encrypted at-rest in iCloud. This is only stated somewhere in a footnote in one of their security documents.
    There are more weak defaults like that in various crucial apps (e.g. WhatsApp) that makes most important stuff available to law enforcement when needed.
    alwillis · 1789579957 · focus · HN ↗
    > Nation states almost certainly have the ability to extract the private keys out of an image sensor and SEP. Outside of superpowers even if you're willing to do it destructively. They can then sign their own fraudulent images.
    That's not how this works.
    Let's pretend they're able to extract the sensor key and the SEP key. Then what?
    An attacker won't have the ECDSA P-256 over SHA-256 signed timestamp token from the Apple Push Notification Service.
    When Reference mode starts, the operating system supplies a SHA-256 digest to be embedded at a fixed location in the captured frame’s metadata. The digest is computed from the most recent secure timestamp, the device manifest, and the device's secure boot manifest.
    More encryption and checking happens until the secure digital negative is sent to Private Cloud Compute:
    PCC recomputes the digest embedded in the frame and verifies the sensor's signature over the pixels and that digest, verifying the certificate chain back to the sensor CA. PCC also verifies the SEP signature and chains it to the BAA CA, and it verifies the signature on the device manifest and chains it to the CA that signs device manifests at the factory. It then confirms that the sensor and SEP named in those chains belong to the same device. Only if all these checks pass does processing continue.
    Only PCC can create an Apple Reference Image; an attacker having the image and sensor private keys doesn't enable them to create a reference image.
    monocasa · 1789593035 · focus · HN ↗
    > An attacker won't have the ECDSA P-256 over SHA-256 signed timestamp token from the Apple Push Notification Service.
    Sure they can, they have everything needed to prove to Apple's servers that they're a real iPhone since pulling the keys means they have the cryptographic root of trust, and Apple's servers will happily be a signature oracle for them in that case.
    > When Reference mode starts, the operating system supplies a SHA-256 digest to be embedded at a fixed location in the captured frame’s metadata. The digest is computed from the most recent secure timestamp, the device manifest, and the device's secure boot manifest.
    And when you know what is measured into those manifests and the keys at the root of trust you can manufacture those too.
    The entire scheme is dependent on not being able to extract device specific keys. At the end of the day, those are almost certainly efuses burnt based on a on-chip HRNG as a manufacturing step which is intended to never leave the device, but instead only signatures and associated public keys.
    But when you have chip development hardware of the kind you'd have at a decent fabless semiconductor company, you can very clearly see burnt efuses.
    alwillis · 1789608827 · focus · HN ↗
    I made a flow chart of the Apple Reference Image process; hopefully it clears up some misconceptions [1].
    [1]: "How pixels become an Apple Reference Image" - <a href="https://news.ycombinator.com/item?id=49735284">https://news.ycombinator.com/item?id=49735284
    monocasa · 1789670359 · focus · HN ↗
    That matches what I said.

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