This post introduces DLR-Lock, a novel defense mechanism for open-weight language models that prevents unauthorized modification of pretrained weights. DLR-Lock replaces standard MLPs with Deep Low-Rank Residual Networks (DLR-Nets), which exploit the inference-training asymmetry of automatic differentiation. This defense forces increased activation memory during backpropagation and creates architectural mismatches that complicate fine-tuning, effectively withstanding adaptive attackers while preserving original model capabilities. Experiments on LLMs validate its efficacy.
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