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arxiv.orgpaper🛡️ Security

Heads of Security: Learned Attention Gates Improve Prompt Injection Robustness

Heads of Security (HoS) is a prompt injection defense that enforces instruction-data separation with learned per-head attention gates, redistributing attention between trusted and untrusted tokens. Evaluated on Llama-3.3-70B-Instruct and GPT-OSS-20B against SecAlign++ and ASIDE. The black-box RL-Hammer attack reaches 97% ASR on GPT-OSS-20B and 85% on SecAlign but 10% on HoS. The white-box Claudini attack needs 3 times more FLOPs on HoS. HoS keeps base-model utility in few-shot settings, where SecAlign and ASIDE degrade.

LlamaGPT-OSS-20BLLM
Heads of Securityprompt injectionSecAlign+++4

AI Security· Added 28 Oct 2026, published 27 Oct 2026

arxiv.orgpaper🧠 AI

Heads of Security: Learned Attention Gates Improve Prompt Injection Robustness

Heads of Security (HoS) is a prompt injection defense that trains a small set of per-head attention gates to shift attention between trusted and untrusted tokens, separating instructions from data. Tested on Llama-3.3-70B-Instruct and GPT-OSS-20B, the black-box RL-Hammer attack reaches 10% ASR on HoS versus 97% on base GPT-OSS-20B and 85% on SecAlign. HoS keeps base utility in few-shot settings, where SecAlign and ASIDE degrade.

TransformerLlamaLLM
Heads of SecuritySecAlign++SecAlign+5

research, training· Added 28 Oct 2026, published 27 Oct 2026

eprint.iacr.orgpaper🛡️ Security

Efficient Laconic Oblivious Transfer with Malicious Security

Efficient Laconic Oblivious Transfer with Malicious Security is an ePrint paper (2026/2593, ASIACRYPT 2026 revision) giving the first maliciously secure laconic OT that uses its primitives only as black boxes. It adds equivocal vector commitments and maliciously secure witness encryption to the commitment-plus-witness-encryption paradigm. Security is proven in the UC model against malicious senders and in the context model against malicious receivers. Instantiations use LWE and bilinear Diffie-Hellman assumptions in the standard model.

laconic oblivious transferequivocal vector commitmentswitness encryption+3

other· Added 24 Oct 2026, published 22 Oct 2026

arxiv.orgpaper🛡️ Security

Stealthy Poisoning Attacks via Reused KV Cache of Reasoning

R^2ECAP (Reused Reasoning-Cache Poisoning) is a black-box attack that plants poisoned reasoning traces through a chat interface, exploiting LLM systems that reuse KV caches of reasoning. A preceding trace steers the model, and the retained trace keeps residual adversarial influence in its cache after the preceding trace is discarded. On three open-weight LLMs and three datasets it reaches up to 79% ASR, beats the white-box HijackKV in 8 of 9 settings, and reaches 46% ASR in a reasoning-trace retrieval system. Only 1% of retained responses are flagged by a popular prompt injection detector.

LLM
R^2ECAPHijackKVprompt injection

AI Security· Added 20 Oct 2026, published 16 Oct 2026

eprint.iacr.orgpaper🛡️ Security

Connecting Cryptanalytic Distinguishers through Divisibility

Paper that links linear, integral, differential-linear and restricted differential distinguishers through two-way conversions with explicit divisibility guarantees and data complexity. It gives automated MILP/SAT models (Walsh and ultrametric representations, exact mix-basis models) and a black-box FWHT histogram search for zeros and finite divisibility. It improves Beyne–Verbauwhede divisibility bounds in 674 SIMON cases (e.g. 2^5 to 2^11 on 9-round SIMON32) and PRESENT. It also gives first higher-divisibility proofs for 8-round SPECK and BEANIE, new bounds for GIFT-64 and Ascon, and new properties on RC5, ChiLow-32, KeeLoq and KATAN32.

SIMONSPECKPRESENT+3
Hosein HadipourBeyne and VerbauwhedeBEANIE+4

other· Published and added 14 Oct 2026

eprint.iacr.orgpaper🛡️ Security

Accelerating Pollard Rho with GPU Field Arithmetic on NVIDIA Blackwell

Preprint that speeds up Pollard rho on GPUs by rebuilding field arithmetic: packed normal-basis representation, the CUDA 13.3 PTX carry-less multiply (clmad), and three-input logic instructions. On one RTX PRO 6000 Blackwell it goes from 0.85 to 14.64 billion iterations/s (17.2x) on the Certicom ECC2K-130 challenge, which puts the whole challenge under five GPU-years. The same levers give 1.52x on P-256 and 2.61x on P-384, which leaves P-256 about 6e21 card-years away. It also reports twelve GPUs from Turing to Blackwell, an FPGA engine on AWS F2 and a campaign that covered 5.4% of the expected work, with code and a Dockerfile on GitHub (rho-blackwell). It claims no improvement on the generic-group bound.

CUDANVIDIA BlackwellAWS+1
Pollard rhoECC2K-130Certicom challenge+5

other· Published and added 14 Oct 2026

eprint.iacr.orgpaper🛡️ Security

Leakage-Resilient Incompressible Cryptography: Constructions and Barriers

Introduces leakage-resilient incompressible cryptography, a security model combining leakage resilience (partial key leakage plus full ciphertext) with incompressibility (full key but only part of the ciphertext or signature). It gives a transformation from incompressible symmetric-key encryption (SKE) to leakage-resilient incompressible SKE, a leakage-resilient incompressible PKE built from a new leakage-resilient non-committing KEM, and an incompressible SKE with ciphertext and compression rate 1/2 using invertible extractors. It also gives a leakage-resilient incompressible signature scheme in the random oracle model under DCR or LWE plus Decisional Linear. Black-box impossibility results show barriers to improving these parameters.

DziembowskiDecisional Linear assumptionLWE+3

other· Added 14 Oct 2026, published 13 Oct 2026

arxiv.orgpaper🧠 AI

Hide and Seek: HIDE Concepts to SEEK explanations for black box models

Hide and Seek (HnS) is a concept-level attribution method for black-box vision models. It needs no model weights and no concept-labeled datasets. Given a concept and an image set, it uses a vision-language model to retrieve concept-aligned images and localize the concept, masks the localized region, and takes attribution from the change in the black-box model's output. It agreed better with ground-truth attributions than existing methods on CelebA and COCO-Stuff, and it works on tasks existing concept attribution methods cannot handle, such as image captioning and satellite image segmentation.

vision-language model
Hide and SeekHnSCelebA+1

research, multimodal· Added 12 Oct 2026, published 9 Oct 2026

arxiv.orgpaper🧠 AI

A Closer Look at Agentic BBO: Benchmarking LLM Agents for Black-Box Optimization

Introduces AgenticBBO-Bench, a benchmark for LLM-agent black-box optimization across synthetic functions, hyperparameter optimization, database tuning, chip design and molecular design under a unified finite-budget protocol. Agentic BBO beats direct LLM methods in all five domains and the best numerical optimizers in four. Ablations show extra numerical tools don't consistently help, task semantics help more than specific priors, and numerical optimizers can absorb gains from agent-found trajectories. A five-task frontier challenge evaluates seven LLMs under the Codex agent harness, with GPT-6 Astra and DeepSeek-V4.1-Flash on the performance-cost Pareto frontier.

Codex
AgenticBBO-BenchGPT-6 AstraDeepSeek-V4.1-Flash

evals, agents, research· Added 9 Oct 2026, published 8 Oct 2026

arxiv.orgpaper🛡️ Security

BRANCH: Bypassing Multi-Scanner AI Guardrails

BRANCH is a bypass methodology for guardrail systems built from multiple scanners (prompt injection/jailbreak detectors). It uses a branching tree search that applies adversarial perturbations to individual scanners and selects techniques based on overall improvement across all scanners, decoupling bypass evaluation from attack signal optimization. It reports 100% attack success across 6 guardrail systems in 120 scenarios with 72% fewer queries and 4.5x lower wallclock time than established techniques, and transfers to 29 unseen guardrails, including 8 commercial black-box ones.

LLM
BRANCH

AI Security· Added 9 Oct 2026, published 7 Oct 2026

eprint.iacr.orgpaper🛡️ Security

Note on Extractability of PST Polynomial Commitment Scheme

This IACR ePrint note revisits a 2025 Crypto paper by Belohorec et al. that proved the PST multivariate polynomial commitment scheme is black-box extractable under two new assumptions, ARSDH(n) and GARSDH(n). The authors show both are in fact equivalent to the original ARSDH assumption from Lipmaa et al. (Eurocrypt 2024), and separately identify a gap in the proof that canonical PST is extractable under GARSDH(n). This matters for implementers and auditors relying on PST/KZG-style polynomial commitments, as it clarifies the actual cryptographic strength underpinning extractability claims used in zk-SNARK and other succinct-proof constructions.

PSTKZG
ARSDHGARSDHBelohorec et al.+3

Blockchain· Added 8 Oct 2026, published 7 Oct 2026

arxiv.orgpaper🛡️ Security

CorrectGuard: Eyes-Off Correctness Estimation for Black-Box Security Guardrails

CorrectGuard is a framework for estimating whether black-box AI security guardrails made correct decisions on inputs that are inaccessible to humans (production privacy) or to the guardrail-auditing model itself, using only labeled "eyes-on" data and no internal access to the guardrail. The authors test in-context-learning, embedding, and finetuning-based correctness classifiers across 13 safety/security datasets (harmful content, jailbreaks, prompt injection, extraction) and multiple open-weight guardrails, showing up to 25-point macro-accuracy gains in error identification and improved risk-based abstention/ranking of guardrail decisions.

LLM

AI Security· Added 5 Oct 2026, published 2 Oct 2026

arxiv.orgpaper🧠 AI

CorrectGuard: Eyes-Off Correctness Estimation for Black-Box Security Guardrails

CorrectGuard is a framework for estimating how accurately black-box security guardrails (jailbreak, harmful-content, prompt-injection and extraction detectors) perform on inputs that cannot be inspected by humans or by the evaluating model itself, using an independent correctness model trained only on labeled "eyes-on" data. The authors test in-context-learning, embedding-based, and fine-tuned correctness classifiers under leave-one-dataset-out evaluation across 13 safety/security datasets and multiple open-weight guardrails, showing up to 25-point macro-accuracy gains and improved risk-coverage tradeoffs (AURC reduced from 0.33–0.44 to 0.17–0.22) for guardrail decision ranking and abstention. The work matters for anyone building auditing or eval pipelines for opaque safety classifiers without privileged access to their internals.

CorrectGuard

evals, research· Added 5 Oct 2026, published 2 Oct 2026

arxiv.orgpaper🛡️ Security

Evaluating and Improving the Robustness of Large Language Models to Input Sequence Variations

Thesis on evaluating and improving LLM robustness to adversarial input perturbations. It proposes the R_stab robustness metric (Jensen-Shannon divergence), ASA, an evolutionary black-box attack on LLM-as-a-Judge systems (up to 73.8% ASR), trojan trigger recovery on Trojan Detection Challenge 2023 (Pythia-1.4B), and a systematization of bypasses of multi-layer defenses from SaTML CTF 2024. For MCP agents it proposes AttestMCP (HMAC-attested tool calls) and the Commit Boundary pattern, cutting ASR from 53.7% to 12.4% on the 847-scenario MCPBench; the methods are implemented in JudgeGuard, TrojanArmor and MCPSec.

LLMModel Context ProtocolPythia+1
ASAR_stabAttestMCP+8

AI Security· Added 9 Oct 2026, published 1 Oct 2026

arxiv.orgpaper🛡️ Security

Evaluating and Improving the Robustness of Large Language Models to Input Sequence Variations

An arXiv thesis-style paper proposing R_stab(f), a Jensen-Shannon-divergence-based robustness metric for LLM outputs under small input perturbations, along with a proven bound V(h) <= 1 - R_class(h) for localized attacks. It introduces ASA, an adaptive evolutionary black-box attack against LLM-as-a-Judge systems reaching up to 73.8% attack success rate (62.6% cross-model transfer), evaluates trojan/backdoor detection on the Trojan Detection Challenge 2023 (Pythia-1.4B) and SaTML CTF 2024, shows that committees of 5-7 heterogeneous models cut Gemma-3-4B's ASR to 19.3%, and presents AttestMCP, an HMAC-based tool-call attestation scheme plus a "Commit Boundary" isolation pattern for MCP agents that cuts average ASR on the 847-scenario MCPBench from 53.7% to 12.4%. Methods ship as the JudgeGuard, TrojanArmor, and MCPSec software suites.

Model Context ProtocolLLMGemma+1
Trojan Detection Challenge 2023SaTML CTF 2024MCPBench+7

AI Security· Added 5 Oct 2026, published 1 Oct 2026

arxiv.orgpaper🛡️ Security

Walking the Embedding Space: Datastore Extraction from Multimodal RAG

Researchers introduce ImmRAG, a black-box data extraction attack against image-returning Multimodal Retrieval-Augmented Generation (MRAG) systems, where the retrieved image itself is the model's response. Instead of malicious text prompts, ImmRAG embeds attack instructions inside an attacker-supplied image and uses relevance-weighted resampling to steer queries toward unexplored regions of the embedding space, progressively reconstructing more of the private datastore. Tested against CLIP-family retrievers across medical, document, and general-purpose scenarios, a single 2500-query run reconstructed up to 611 radiology images, 566 document scans, and 416 general images — up to 5.6x more distinct items than a non-adaptive baseline — highlighting the lack of safeguards against multimodal data leakage.

CLIP
ImmRAG

AI Security· Added 2 Oct 2026, published 1 Oct 2026

arxiv.orgpaper🛡️ Security

Do Defenses Against LLM Extraction Work Across Attacks? A Lifecycle Benchmark of Black-Box Model Extraction

This arXiv paper presents a reproducible benchmark that unifies evaluation of six black-box LLM extraction attacks, ten defenses, and two adaptive attacks (paraphrasing and back-translation of protected responses) under controlled query budgets and model configurations. It measures surrogate capability, fidelity to the victim model, output quality (Rep-4), and provenance-detector scores, giving a consistent basis for comparing how extraction methods and defenses interact under text-only API access. Code and artifacts are linked from the paper.

LLM
Rep-4

AI Security· Added 3 Oct 2026, published 30 Sep 2026

arxiv.orgpaper🧠 AI

Probability is Not Enough: Exploring and Counting Divergent Tokens for Reasoning Uncertainty Quantification in LLMs

This paper introduces Divergent Token Confidence (DTC), a method for uncertainty quantification in LLM chain-of-thought reasoning that counts tokens where two models strongly disagree during decoding, measured via Jensen-Shannon divergence between next-token distributions on the same reasoning trajectory. Unlike standard probability-based confidence scores, DTC requires no training, works in both white-box and black-box settings, and its divergent-token count is shown to be strongly negatively correlated with answer accuracy. Across six mathematical benchmarks and multiple model families (including DeepSeek-V3.2), DTC cuts expected calibration error roughly in half compared to full-sequence probability and verbalized-confidence baselines (e.g., 13.0% vs 32.7%-42.4% white-box).

DeepSeek-V3.2

evals, research· Added 30 Sep 2026, published 29 Sep 2026

arxiv.orgpaper🧠 AI

Clean Engineering, Unstable Measurement: A Preregistered Reliability Failure of Black-Box LLM Observers on Shared Endpoints

This preregistered study audits whether black-box LLM judges give stable, reproducible readings on shared serving endpoints, running two campaigns across 52,988 request attempts. Same-window repeat rankings only reached Spearman 0.400 against a required 0.90, and byte-identical next-day replays agreed at 0.78 against a required 0.99, showing that a model name on a shared endpoint is not a frozen measurement instrument. The authors trace the failure to label-to-meaning mapping bias, tiny candidate gaps relative to instrument noise, and non-deterministic outputs on identical inputs, and propose a three-level snapshot-identity ladder plus design rules and a reporting checklist for anyone freezing eval gates on LLM judges.

evals· Added 26 Sep 2026

arxiv.orgpaper🛡️ Security

RedEvoAgent: Automatic Red-Teaming Agent with Experience-Driven Skill Evolution

RedEvoAgent is a black-box automatic red-teaming agent that distills successful jailbreak trajectories into concise, human-readable 'attack skills' rather than retrieving full past trajectories. It evolves these skills via tool-effectiveness profiling and a validation ratchet that only keeps updates improving attack success, and is shown to outperform fixed and agentic jailbreak baselines while transferring across attacker models and target execution harnesses (product-level agent environments where jailbreaks trigger real tool use, not just unsafe text).

LLM

AI Security· Added 26 Sep 2026

arxiv.orgpaper🛡️ Security

Decoy Images Amplify Caption-Mediated Defenses Against Encoded Jailbreaks

Researchers report that attaching an unrelated "decoy" image to an encoded jailbreak prompt can sharply cut attack success rate against caption-mediated black-box VLM defenses like ECSO — up to 73 percentage points — even though the image itself is content-free, across five frontier VLMs, two encoded-attack families, and three defenses. Controls show the effect stems from image presence (not content or vendor filtering) and holds even under adaptive attacks targeting the caption re-check, but unconditional decoy attachment inflates benign refusal rates by 10–67pp, so the authors propose gating it on a lightweight encoded-input detector. The paper was withdrawn by the author after v2, so treat conclusions as unverified/retracted.

ECSO

AI Security· Added 26 Sep 2026

arxiv.orgpaper🛡️ Security

GAS-Leak-LLM: Genetic Algorithm-Based Suffix Optimization for Black-Box LLM Jailbreaking

GAS-Leak-LLM is a black-box jailbreaking attack that uses a genetic algorithm (selection, mutation, crossover) to evolve adversarial suffixes appended to prompts, bypassing LLM safety alignment without needing model weights or gradients. The paper reports empirical results showing existing content-moderation and alignment safeguards on commercial LLMs can be defeated through this iterative, query-only search over the discrete prompt space.

LLM
GAS-Leak-LLM

AI Security· Added 26 Sep 2026

arxiv.orgpaper🧠 AI

Statistical attribute alignment for black-box generative AI via output post-processing

This arXiv paper addresses aligning the distribution of an attribute in a black-box generative AI model's outputs, such as fairness attributes or synthetic data representativeness, with a user-specified target distribution, using only repeated query access without model internals. The authors develop query-minimizing post-processing algorithms for exact and approximate alignment across multiple generated outputs, proving asymptotic optimality, and validate the approach on text-to-image generation and geocoded persona generation tasks.

text-to-image generation
geocoded persona generation

research, multimodal· Added 28 Sep 2026, published 25 Sep 2026

arxiv.orgpaper🛡️ Security

Region-Level Black-Box Defense Against Stealthy Embedding-Space Backdoors in CLIP

CLIPGuard is a fully black-box defense against embedding-space backdoor attacks in CLIP, which poison a tiny fraction of image-text pairs to implant stealthy triggers that shift the joint embedding space without needing model parameters, gradients, or clean validation data. It detects malicious image regions by measuring segment-wise embedding perturbations and purifies only suspicious segments via semantic inpainting, reducing attack success rate to 1.05% while keeping clean accuracy at 86.34% on STL-10 and ImageNet against BadCLIP, BadNets, blended, patch-based, and typographic triggers, outperforming CleanCLIP and CleanerCLIP.

CLIPCLIPGuard
BadCLIPBadNetsCleanCLIP+3

AI Security· Added 28 Sep 2026, published 25 Sep 2026

arxiv.orgpaper🛡️ Security

A2M: Trace-Optimized Agent Hijacking in the MCP Ecosystem

A2M (Attraction-to-Manipulation) is a two-stage black-box framework for hijacking agents that use the Model Context Protocol to select tools from third-party MCP servers. The Attraction phase optimizes attacker-controlled tool metadata to raise invocation probability, while the Manipulation phase uses execution traces to craft adversarial tool outputs that steer agent behavior; on LiveMCPBench it achieves a 93.6% malicious tool invocation rate against GLM-4.6, inflates token cost 32.4x under a cognitive denial-of-service variant, and reaches a 74.4% mean attack success rate across information exfiltration, environment integrity compromise, and reasoning derailment, with partial transfer (63.6%/2.7x/24.5%) to four other models without re-optimization. The authors argue this exposes a semantic supply-chain risk in MCP tool ecosystems and call for stronger tool vetting and runtime isolation.

Model Context ProtocolGLM
LiveMCPBenchA2MCognitive Denial of Service

AI Security· Added 2 Oct 2026, published 22 Sep 2026

arxiv.orgpaper🛡️ Security

Feedback Coding Enables Inference-Time Covert Agentic Communication

This arXiv paper (cs.IT, submitted Sep 2026) reframes black-box LLM steganography as a sequential communication problem with causal feedback, introducing Burnashev Adaptive Posterior Matching (BAM) — a feedback-coding scheme combining posterior matching with a decode-and-confirm phase, backed by a cryptographic reduction proof for its security. Tested across three open-weight LLMs, BAM achieves 0-0.1% message error on 8-bit payloads in ~50 tokens (vs 10-17% for the strongest black-box baseline), and the authors demonstrate a full end-to-end covert communication protocol usable within ordinary-looking conversational text. This matters for AI security as it shows how agents/models could exchange hidden payloads inside seemingly benign LLM output, evading white-box watermark detection.

LLM
Burnashev Adaptive Posterior Matching (BAM)

AI Security· Added 22 Sep 2026, published 21 Sep 2026

arxiv.orgpaper🧠 AI

LIMBO: Learning and Internalizing Model-Free Barrier Objectives for Agile and Safe Whole-Body Control

LIMBO is a framework for synthesizing a state-action control barrier function (Q-CBF) from black-box transitions and distilling its safety structure into a task policy, avoiding the need for an online safety filter at deployment. Applied to a 29-degree-of-freedom humanoid performing dodgeball avoidance and low-obstacle locomotion, it uses risk-guided sampling near the boundary of recoverability during synthesis and acts as a safety-feedback teacher during task learning, transferring to hardware without online filtering.

LIMBO

research, multimodal· Added 22 Sep 2026, published 18 Sep 2026

arxiv.orgpaper🧠 AI

The More It Says, the More You Pay: A Black-Box Audit of Provider-Side Token Inflation in LLM Services

This arXiv preprint defines and studies "Provider-Side Token Inflation Attacks" (PTIA), where LLM API providers covertly manipulate generation to produce longer outputs (and thus higher bills) while preserving task utility, testing five attack variants at the query, prompt, representation, and model levels that each inflate output length over 10x baseline. The authors identify a "PTIA saturation" effect tied to end-of-sequence token probability suppression, and build a lightweight single-probe black-box audit (no trusted reference model needed) that detects PTIA with 85.1% average detection rate and under 2% false-positive rate across four open-weight models, flagging 7 of 15 real-world LLM API services as PTIA-consistent.

ai-infra, research· Added 22 Sep 2026, published 17 Sep 2026

arxiv.orgpaper🛡️ Security

The More It Says, the More You Pay: A Black-Box Audit of Provider-Side Token Inflation in LLM Services

This arXiv paper defines Provider-Side Token Inflation Attacks (PTIA), where a dishonest LLM API provider covertly manipulates generation at the query, prompt, representation, or model level to inflate billed output tokens while preserving apparent task quality. The authors instantiate five such attacks (each pushing mean output length past 10.2x baseline), identify a "PTIA saturation" effect tied to suppressed end-of-sequence token probability, and build a lightweight single-probe black-box audit that needs no trusted reference model, achieving 85.1% detection with under 2% false positives across four open-weight models — and flags 7 of 15 real-world LLM API services as PTIA-consistent.

LLM
Provider-Side Token Inflation AttackPTIA saturation

AI Security· Added 18 Sep 2026, published 17 Sep 2026

arxiv.orgpaper🛡️ Security

PISmith: Reinforcement Learning-based Red Teaming for Prompt Injection Defenses

PISmith trains an attack LLM with GRPO in a black-box setting to generate injected prompts that defeat prompt-injection defenses. It addresses extreme reward sparsity, which causes entropy collapse in standard GRPO, with adaptive entropy regularization and dynamic advantage weighting. Evaluated on 13 benchmarks against 8 defenses and 7 baselines (static, search-based such as TAP and PAIR, and RL-Hammer), it achieves the highest attack success rates and also works on InjecAgent and AgentDojo against GPT-4o-mini and GPT-5-nano. It shows state-of-the-art defenses such as Meta-SecAlign remain vulnerable to adaptive attacks.

LLMAgentDojo
PISmithRL-HammerTAP+8

AI Security· Added 17 Sep 2026

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