Aligning Logits Generatively for Principled Black-Box Knowledge Distillation in the Wild

Black-Box Knowledge Distillation (B2KD) is a conservative task in cloud-to-edge model compression, emphasizing the protection of data privacy and model copyrights on both the cloud and edge. With invisible data and models hosted on the server, B2KD aims to utilize only the API queries of the teacher model's inference results in the cloud to effectively distill a lightweight student model deployed on edge devices. B2KD faces challenges such as limited Internet exchange and edge-cloud disparity in data distribution. To address these issues, we theoretically provide a new optimization direction from logits to cell boundary, different from direct logits alignment, and formalize a workflow comprising deprivatization, distillation, and adaptation at test time. Guided by this, we propose a method, Mapping-Emulation KD (MEKD), to enhance the robust prediction and anti-interference capabilities of the student model on edge devices for any unknown data distribution in real-world scenarios. Our method does not differentiate between treating soft or hard responses and consists of: 1) deprivatization: emulating the inverse mapping of the teacher function with a generator, 2) distillation: aligning low-dimensional logits of the teacher and student models by reducing the distance of high-dimensional image points, and 3) adaptation: correcting the student's online prediction bias through a graph propagation-based only-forward test-time adaptation algorithm. Our method demonstrates inspiring performance for edge model distillation and adaptation across different teacher-student pairs. We validate the effectiveness of our method on multiple image recognition benchmarks and various Deep Neural Network models, achieving state-of-the-art performance and showcasing its practical value in remote sensing image recognition applications.