Category Archives: Technology

Invisible Image Watermarks Are Provably Removable Using Generative AI

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Generative AI is the current hot topic. Of course, one of the newest challenges is to discriminate a genuine image from a generative-AI-produced one. Many papers propose systematically watermarking the generative AI outputs.

This approach makes several assumptions. The first one is that the generator is actually adding an invisible watermark. The second assumption is that the watermark survives most transformations.

In the content protection field, we know about the validity of the second assumption. Zhao et al., from the University of California Santa Barbara and Carnegie Mellon University, published a paper. The system adds Gaussian noise to the watermarked image and reconstructs the same image using the noise image. After several iterations, the watermark disappears. They conclude that any watermark can be defeated.

This is a well known fact in the watermark community. The Break Our Watermark System (BOWS) in 2006 and the BOWS2 in 2010 demonstrated this reality. These contests aimed to demonstrate that attackers can defeat the watermark if they have access to an oracle watermark detector.

Thus, this paper illustrates this fact. Their contribution adds generative AI to the attacker’s toolset. As a countermeasure, they propose to use a semantic watermark. The semantic watermark changes the image but keeps its semantic information (or at least some). This approach is clearly not usable for content protection.

Reference

Zhao, Xuandong, Kexun Zhang, Zihao Su, Saastha Vasan, Ilya Grishchenko, Christopher Kruegel, Giovanni Vigna, Yu-Xiang Wang, and Lei Li. “Invisible Image Watermarks Are Provably Removable Using Generative AI.” arXiv, August 6, 2023. https://arxiv.org/pdf/2306.01953.pdf.

Craver, Scott, Idris Atakli, and Jun Yu. “How We Broke the BOWS Watermark.” In Proceedings of the SPIE, 6505:46. San Jose, CA, USA: SPIE, 2007. https://doi.org/10.1117/12.704376.

“BOWS2 Break Our Watermarking System 2nd Ed.” http://bows2.ec-lille.fr/.

Black Hat 2023 Day 1

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  1. Introduction (J. MOSS)

Jeff MOSS (Founder of DefCon and Black Hat) highlighted some points:

  • AI is about using predictions. 
  • AI brings new issues with Intellectual Properties.   He cited the example of Zoom™ that just decided that all our interactions could be used for their ML training.
  • Need for authentic data.

The current ML models are insecure, but people trust them.  Labs had LLMs available for many years but kept them.  With OpenAI going public, it started the race.

She presents trends for enterprise:

  • Enterprise’s answer to ChatGPT is Machine Learning as a Service (MLaaS).  But these services are not secure.
  • The next generation should be multi-modal models (using audio, image, video, text…).  More potent than monomodal ones such as LLMs.
  • Autonomous agent mixes the data collection of LLM and takes decisions and actions.  These models will need secure authorized access to enterprise data.  Unfortunately, their actions are non-deterministic.
  • Data security for training is critical.  It is even more challenging when using real-time data.

She pointed to an interesting paper about poisoning multi-modal data via image or sound.

Often, the power LED is more or less at the entry of the power supply circuit.  Thus, intensity is correlated to the consumption.

They recorded only the image of the LED to see the effect of the rolling shutter.  Thus, they increase the sampling rate on the LED with the same video frequency.  This is a clever, “cheap” trick.

To attack ECDSA, they used the Minerva attack (2020)

Conclusion: They turned timing attacks into a power attack.  The attacks need two conditions:

  1. The implementation must be prone to some side-channel timing attack.
  2. The target must have a power LED in a simple setting, such as a smart card reader, or USB speakers. 

Despite these limitations, it is clever.

Once more, users trust AI blindly.

The global environment is complex and extends further than ML code.

All traditional security issues are still present, such as dependency injection.

The current systems are not secure against adversarial examples.  They may not even present the same robustness of all data points.

Explainability is insufficient if it is not trustworthy.  Furthermore, the fairness and trustworthiness of the entity using the explanation are essential.

The Multi-Party Computation (MPC) Lindel17 specifies that all further interactions should be blocked when a finalized signature fails.  In other words, the wallet should be blocked.  They found a way to exfiltrate the part key if the wallet is not blocked (it was the case for several wallets)

In the case of GG18 and GG20, they gained the full key by zeroing the ZKP using the CRT (Chinese Remainder Theorem) and choosing a small factor prime.

Conclusion: Adding ZKP in protocols to ensure that some design hypotheses are enforced.

They created H26forge to create vulnerable H264 content.  They attack the semantics out of its specified range.  Decoders may not test all of them.  The tool helps with handling the creation of forged H264. 

Conclusion

This may be devastating if combined with fuzzing.

Enforce the limits in the code.

If the EKU (extended key use) is not properly verified for its purpose, bingo.

Some tested implementations failed the verification.  The speaker forged the signing tools to accept domain-validated certificates for signing code.

Politically correct but not really informative.

IS RSA2048 broken?

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Recently, an academic paper from a large team of Chinese researchers made the headlines of the specialized press [1].  Reporters claimed that “small” quantum computers may break RSA2048.  Breaking RSA2048 may need only 372 qubits.  Qubits are similar to bits in the quantum domain.  IBM already proposes Osprey: a 433-qubit chip.  So, is RSA2048 dead?

The security of RSA relies on the assumption that factorizing the product of two large prime numbers is extremely difficult.  It is assumed currently that conventional computers cannot solve this problem.  Recent studies showed that, in theory, quantum computers may succeed.

The paper is not for the faint heart.  Its summary is as follows:

Shor’s algorithm has seriously challenged information security based on public key cryptosystems.  However, to break the widely used RSA-2048 scheme, one needs millions of physical qubits, which is far beyond current technical capabilities.  Here, we report a universal quantum algorithm for integer factorization by combining the classical lattice reduction with a quantum approximate optimization algorithm (QAOA).  The number of qubits required is O(logN/loglog N), which is sublinear in the bit length of the integer $N$, making it the most qubit-saving factorization algorithm to date.  We demonstrate the algorithm experimentally by factoring integers up to 48 bits with 10 superconducting qubits, the largest integer factored on a quantum device.  We estimate that a quantum circuit with 372 physical qubits and a depth of thousands is necessary to challenge RSA-2048 using our algorithm.  Our study shows great promise in expediting the application of current noisy quantum computers, and paves the way to factor large integers of realistic cryptographic significance.

As mentioned, RSA’s security assumes it is tough to factorize the product of two very large prime numbers.  The researchers use Schnorr’s algorithm [2] to factor these large numbers rather than the Schor one.  On the one hand, the Schor algorithm requires millions of qubits, but it is a theoretically proven solution.  Unfortunately, it is out of the current feasibility realm.  On the other hand, Schnorr’s algorithm seems not yet to be a proven solution at a large scale.  The expected speed-up using quantum computing is highly controversial and not demonstrated.  The paper stays in the realm of unproven expectations.

The consensus seems to be that the threat is not yet here.  Following is a list of posts of people who know far better than me:

  • [3] highlights one crucial point (present in all papers): It should be pointed out that the quantum speed-up of the algorithm is unclear due to the ambiguous convergence of QAOA.  In other words, the paper does not demonstrate that it is faster than Schor’s.  Scott is a quantum computing expert.
  • [4] highlights that the paper never claims to be faster.  It omits “running time”; what is merely claimed is that the quantum circuit is very small.
  • [5] Bruce Schneier reminds that Schnorr’s paper works well for small moduli, but does not scale well for larger prime numbers.
  • [6] highlights that the quantum computer should have a 99.999% fidelity.  This would require a NISQ computer with gate level fidelities of 99.999%.  That level is more than two orders of magnitude better than the best machines we have today. 

Conclusion

Keep calm.  RSA 2048 is still safe for many years.  Nevertheless, it is key to be aware of the latest progress of post-quantum cryptography.  Do we have to switch to post-quantum cryptography?  Not right now, especially if you do not handle secrets that have to last for many decades.

Reference

[1]          B. Yan et al., “Factoring integers with sublinear resources on a superconducting quantum processor.” arXiv, Dec. 23, 2022.   Available: http://arxiv.org/abs/2212.12372

[2]          C. P. Schnorr, “Fast Factoring Integers by SVP Algorithms, corrected.” 2021.  Available: https://eprint.iacr.org/2021/933

[3]          S. Aaronson, “Cargo Cult Quantum Factoring,” Shtetl-Optimized, Jan. 04, 2023.  https://scottaaronson.blog/?p=6957

[4]          “Paper claims to break RSA-2048 with only 372 physical quibits.” https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/AkfdRQS4yoY/m/3plDftUEAgAJ .

[5]          “Breaking RSA with a Quantum Computer – Schneier on Security.” https://www.schneier.com/blog/archives/2023/01/breaking-rsa-with-a-quantum-computer.html

[6]          dougfinke, “Quantum Experts Debunk China Quantum Factoring Claims,” Quantum Computing Report, Jan. 06, 2023.  https://quantumcomputingreport.com/quantum-experts-debunk-china-quantum-factoring-claims

NIST selected the post-quantum cryptosystems

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Post-quantum cryptography encompasses the algorithms that are allegedly immune to quantum computing.  In 2017, NIST initiated the process of selecting and standardizing a set of post-quantum cryptosystems. In 2020, NIST started the third round with 15 remaining candidates.

NIST announced the four winners.  CRYSTALS-KYBER is the new key establishment protocol for post-quantum. 

“Among its advantages are comparatively small encryption keys that two parties can exchange easily, as well as its speed of operation. ”

CRYSTALS-DILITHIUM, Falcon, and SPHINCS+ are the new digital signature systems.

“ Reviewers noted the high efficiency of the first two, and NIST recommends CRYSTALS-Dilithium as the primary algorithm, with FALCON for applications that need smaller signatures than Dilithium can provide. The third, SPHINCS+, is somewhat larger and slower than the other two, but it is valuable as a backup for one chief reason: It is based on a different math approach than all three of NIST’s other selections.”

Interestingly, version 9.0 of OpenSSH proposes a post-quantum algorithm.  It is NTRU prime and not CRYSTALS-KYBER.

OpenSSH prepares post-quantum

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For several years, cryptography has studied the implication of the rise of quantum computation.  Once fully operational, with enough qubits, error-free, and keeping quantum states long enough, quantum computing will break prime number factor-based cryptosystems (such as RSA) and Elliptic Curve Cryptography by quickly finding the private keys.

Thus, in 2017, NIST initiated selecting and standardizing a set of post-quantum cryptosystems.

OpenSSH just released version 9.0.  And it adds the support of a post-quantum cryptosystem.  To be precise:

Quoting

use the hybrid Streamlined NTRU Prime + x25519 key exchange method by default (“sntrup761x25519-sha512@openssh.com”). The NTRU algorithm is believed to resist attacks enabled by future quantum computers and is paired with the X25519 ECDH key exchange (the previous default) as a backstop against any weaknesses in NTRU Prime that may be discovered in the future.  The combination ensures that the hybrid exchange offers at least as good security as the status quo.

NTRU Prime is one of the nine remaining candidates in the NIST selection process.   OpenSSH chose one without waiting for the NIST final selection. 

Breaching the Samsung S9 Keystore

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Most Android devices implement an Android Hardware-backed Keystore.  The Rich Execution Environment (REE) applications, i.e., the unsecure ones, use a hardware root of trust and an application in the Trusted Execution Environment (TEE).  Usually, as all the cryptographic operations occur only in the trusted part, these keys should be safe.

Three researchers from the Tel-Aviv university demonstrated that it is not necessarily the case.  ARM’s TrustZone is one of the most used TEEs.  Each vendor must write its own Trusted Application (TA) that executes in the TrustZone for its key store.  The researchers reverse-engineered the Samsung implementation for S8, S9, S20, and S21.  They succeeded in breaching the keys protected by the key store.

The breach is not due to a vulnerability in TrustZone.  It is due to design errors in the TA.

When REE requests to generate a new key, the TA returns a wrapped key, i.e., a key encrypted with a key stored in the root of trust.  In a simplified explanation, the wrapped key is the newly generated key AES-CGM-encrypted with an IV provided by the REE application and a Hardware-Derived Key (HDK) derived from some information supplied by the REE application and the hardware root of trust key.

 In other words, the REE application provides the IV and some data that generate the HDK.  AES-CGM is a stream cipher (uses AES CTR), and thus it is sensitive to IV reuse.  With a streamcipher, you must never reuse an IV with the same key.  Else, it is easy to retrieve the encrypted message with a known ciphertext.  In this case, the attacker has access to the IV used to encrypt the wrapped key and can provide the same `seed` for generating the HDK.   Game over!

In S20 and S21, the key derivation function adds some randomness for each new HDK.  The attacker cannot anymore generate the same HDK.  Unfortunately, the S20 andS21 TA contains the old derivation function.  The researchers found a way to downgrade to the S9 HDK.  Once more, game over!

Lessons:

  1. Never reuse an IV with a streamcipher.  Do not trust the user to generate a new IV, do it yourself.
  2. A Trusted Execution Environment does not protect from a weak/wicked “trusted” application. 
  3. If not necessary, remove all unused software from the implementation.  You reduce the attack surface.

Reference

A. Shakevsky, E. Ronen, and A. Wool, “Trust Dies in Darkness: Shedding Light on Samsung’s TrustZone Keymaster Design,” 208, 2022.  Available: http://eprint.iacr.org/2022/208

The fall of Titans?

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Two French security researchers, Victor Lomne and Thomas Roche, published in January an impressive 55-page report.  The report describes a successful Electro-Magnetic side-channel attack on Google’s Titan security key.  They succeeded in extracting the ECDSA private key.

Titan security key is a FIDO U2F compliant key also known as Google authenticator.  It is functionally similar to Yubikeys.  Its purpose is to serve as a physical token for Two-Factor Authentication (2FA).

Mounting side-channel attacks on secure components like smart cards is “common.”  It usually assumes the attacker has samples to analyze and that the attacker can store arbitrary known secrets in the samples.  This knowledge provides some reference points during the attack.  Once the attack is fine-tuned with the samples using a known secret, it is possible to extract the target’s secret. Unfortunately, this is not true in this specific use case.  When registering, the token generates its ECDSA key pair.  The private key never leaves the token.  It is why it is not possible to back up such tokens.  Thus, it is possible to purchase Titan tokens, but not to feed an arbitrary key pair.  The researchers used an interesting methodology to overcome this issue.

They first identified the secure component used by Titan. They removed the plastic cover and identified NXP A7005.  They found out that some JavaCards have similar characteristics to the NXP A7005.  Thus, they used JavaCards using NXP P5x chips.

Using a 500µm coil with 10µm precision micromanipulators, they measured the EM signature of the ECDSA signing for both Titan and the JavaCard.  The comparison of the two EM signatures confirmed that they used the same implementation.  Thus, they concentrated their effort on the Javacard to design the exploit.  They reverse-engineered the implementation using the EM traces to guess the calculations. They discovered a sensitive leakage and could mount a complex side-channel attack.  The document details the complexity of the attack.  With 4,000 sampled signatures for 2TB of data, they succeeded in extracting the key that they fed to the smart card.

Then, they implemented the same attack on the Titan chip.  They increased the number of samples to 6,000 for 3TB of data.   They succeeded in extracting the private key.

How devastating is this attack?

  • The specialized equipment is about 10K€ (about $12K). The needed skill set is high.  On the  Common Criteria (CC) scale, it has a rating of 27 corresponding to attackers with moderate attack potential.  The corresponding chips are old and are not any more covered by CC certificates.
  • The attack requires the attacker to get the Titan key for several hours to collect the 6,000 samples.  It is not possible to clone it.
  • The attack requires opening the plastic casing.  The operation seems destructive.  For stealthiness, the attacker must be able to repackage the chip in a legitimate case.
  • The attacker needs to return the “borrowed” recased key to the legitimate owner. Else this owner may detect the loss and block the access.
  • This attack impacts not only the Titan token but a long list of components.

Thus, we may forecast that such attack would be efficient only against very high-profile targets.

Conclusions

The attack is an impressive piece of work.  Reading the document gives an overview of the issues a side-channel attack requires to solve. It is extremely interesting.

Diversity of implementation across different products is a costly but secure option.

Continue to use your 2FA tokens.  It is more secure than not using them.  If you lost your 2FA token, change your accounts to use a new one as soon as possible (which should be the case, independently of this attack).

Use 2FA tokens as much as possible.

Reference

Lomne, Victor, and Thomas Roche. “A Side Journey to Titan.” NinjaLab, January 7, 2021. https://ninjalab.io/wp-content/uploads/2021/01/a_side_journey_to_titan.pdf.