There are also thieves in large models? To protect your parameters, submit the large model to make a "human-readable fingerprint"

Different base models are symbolized as different breeds of dogs, and the same "dog-shaped fingerprint" indicates that they are derived from the same base model.

Pre-training of large models requires a large amount of computing resources and data. Therefore, the parameters of pre-trained models have become the core competitiveness and assets that major institutions focus on protecting. However, unlike traditional software intellectual property protection, there are two new problems in judging the misappropriation of pre-trained model parameters:

1) The parameters of pre-trained models, especially those of hundreds of billions of models, are usually not Will be open source.

The output and parameters of the pre-trained model will be affected by subsequent processing steps (such as SFT, RLHF, continue pretraining, etc.), which makes it difficult to judge whether a model is fine-tuned based on another existing model. Whether judging based on model output or model parameters, there are certain challenges.

Therefore, the protection of large model parameters is a new problem that lacks effective solutions.

The Lumia research team of Professor Lin Zhouhan of Shanghai Jiao Tong University has developed an innovative technology that can identify ancestry relationships between large models. This approach employs a human-readable fingerprint of a large model without exposing model parameters. The research and development of this technology is of great significance to the development and application of large models.

This method provides two discrimination methods: one is a quantitative discrimination method, which determines whether the pre-trained base model has been stolen by comparing the similarity between the tested large model and a series of base models; the other is Qualitative judgment method, quickly discover the inheritance relationship between models by generating human-readable "dog pictures".

^{Fingerprints for 6 different base models (first row) and their corresponding descendant models (bottom two rows).}

^{Human-readable large model fingerprints produced for 24 different large models.}

Motivation and overall approach

The rapid development of large-scale models has brought a wide range of application prospects, but it has also triggered a series of new challenge. Two of the outstanding problems include:

• Model theft problem: A clever "thief" who only made minor adjustments to the original large model, and then He claimed to have created a brand new model and exaggerated his contribution. How do we identify if it's a pirated model?

• Model Abuse Issue: When a criminal maliciously modifies the LLaMA model and uses it to generate harmful information, even though Meta’s policy clearly prohibits this behavior, how do we Prove that it uses the LLaMA model?

Previously, conventional methods to solve this type of problem included adding watermarks during model training and inference, or adding watermarks to the images generated by large models. Text is classified. However, these methods either impair the performance of large models or are easily circumvented by simple fine-tuning or further pretraining.

This raises a key question: Is there a method that does not interfere with the output distribution of a large model, is robust to fine-tuning and further pretrain, and can also accurately track the base model of the large model, so that The purpose of effectively protecting model copyright.

A team from Shanghai Jiao Tong University drew inspiration from the unique characteristics of human fingerprints and developed a method to create "human-readable fingerprints" for large models. They symbolized different base models as different breeds of dogs, with the same "dog-shaped fingerprint" indicating that they were derived from the same base model.

This intuitive method allows the public to easily identify the connections between different large models, and trace the base model of the model through these fingerprints, effectively preventing model piracy and abuse. It is worth noting that manufacturers of large models do not need to publish their parameters, only the invariants used to generate fingerprints.

The "fingerprints" of Alpaca and LLaMA are very similar. This is because the Alpaca model is obtained by fine-tuning LLaMA; while the fingerprints of several other models show obvious The difference reflects that they originate from different base models.

The paper "HUREF: HUMAN-READABLE FINGERPRINT FOR LARGE LANGUAGE MODELS":

Paper download address: https://arxiv.org/pdf/2312.04828.pdf

Invariant terms observed from experiments

The Jiaotong University team found that when fine-tuning or further pretraining large models, the direction of the parameter vectors of these models changes very slightly. In contrast, for a large model trained from scratch, its parameter direction will be completely different from other base models.

They were verified on a series of derivative models of LLaMA, including Alpaca and Vicuna obtained by fine-tuning LLaMA, as well as Chinese LLaMA and Chinese LLaMA obtained by further pretraining LLaMA Chinese Alpaca. In addition, they also tested independently trained base models such as Baichuan and Shusheng.

The LLaMA derivative model marked in blue in the table and the LLaMA-7B base model show extremely high cosine similarity in the parameter vector, which means that these derivative models It is very close to the base model in the parameter vector direction. In contrast, the independently trained base models marked in red present a completely different situation, with their parameter vector directions completely unrelated.

Based on these observations, they considered whether they could create a fingerprint of the model based on this empirical regularity. However, a key question remains: is this approach robust enough against malicious attacks?

In order to verify this, the research team added the similarity of parameters between models as a penalty loss when fine-tuning LLaMA, so that the parameter direction of the model deviates as much as possible from the base model while fine-tuning, and the test model can Whether to deviate from the original parameter direction while maintaining performance:

They tested the original model and the model obtained by adding penalty loss fine-tuning on 8 benchmarks such as BoolQ and MMLU. As you can see from the chart below, the model's performance deteriorates rapidly as the cosine similarity decreases. This shows that it is quite difficult to deviate from the original parameter direction without damaging the ability of the base model!

Currently, the parameter vector direction of a large model has become an extremely effective and robust indicator for identifying its base model. However, there seem to be some problems in directly using the parameter vector direction as an identification tool. First, this approach requires revealing the parameters of the model, which may not be acceptable for many large models. Secondly, the attacker can simply replace the hidden units to attack the direction of the parameter vector without sacrificing model performance.

Taking the feedforward neural network (FFN) in Transformer as an example, by simply replacing the hidden units and adjusting their weights accordingly, the weight direction can be achieved without changing the network output. Modifications.

#In addition, the team also conducted in-depth analysis of linear mapping attacks and displacement attacks on large model word embedding. These findings raise a question: How should we effectively respond and solve these problems when faced with such diverse attack methods?

They derived three sets of invariants that are robust to these attacks by eliminating the attack matrices through multiplication between parameter matrices.

From invariants to human-readable fingerprints

Although the invariants derived above are sufficient as large-scale identity markers, but they usually appear in the form of huge matrices, which are not only unintuitive, but also require additional similarity calculations to determine the relationship between different large models. Is there a more intuitive and understandable way to present this information?

In order to solve this problem, the Shanghai Jiao Tong University team developed a method for generating human-readable fingerprints from model parameters—HUREF.

They first extracted invariants from some parameters of the large model, and then used CNN Encoder to encode the invariant matrix into a obeying method while maintaining locality. Gaussian distributed feature vectors, and finally use a smooth GAN or VAE as an image generator to decode these feature vectors into visual images (i.e., dog pictures). These images are not only human-readable, but also visually demonstrate the similarities between different models, effectively serving as a "visual fingerprint" for large models. The following is the detailed training and inference process.

In this framework, the CNN Encoder is the only part that needs to be trained. They use contrastive learning to ensure the local preservation of the Encoder, while using generative adversarial learning to ensure that the feature vector obeys a Gaussian distribution, consistent with the input space of the GAN or VAE generator.

Importantly, during the training process, they do not need to use any real model parameters, all data are obtained through normal distribution sampling. In practical applications, the trained CNN Encoder and the off-the-shelf StyleGAN2 generator trained on the AFHQ dog data set are directly used for inference.

Generating fingerprints for different large models

In order to verify the effectiveness of this method, the team conducted experiments on a variety of widely used large models. They selected several well-known open source large models, such as Falcon, MPT, LLaMA2, Qwen, Baichuan and InternLM, as well as their derivative models, calculated the invariants of these models, and generated the fingerprint image as shown in the figure below. .

The fingerprints of the derived models are very similar to their original models, and we can intuitively identify from the images which prototype model they are based on. In addition, these derived models also maintain a high cosine similarity with the original model in terms of invariants.

Subsequently, they conducted extensive testing on the LLaMA family of models, including Alpaca and Vicuna obtained by SFT, models with extended Chinese vocabulary, Chinese LLaMA and BiLLa obtained by further pretrain, and RLHF Beaver and the multi-modal model Minigpt4, etc.

The table shows the cosine similarity of invariants between LLaMA family models. At the same time, the picture shows the fingerprint images generated for these 14 models. Their similarities The degree is still very high. We can judge from the fingerprint images that they come from the same model. It is worth noting that these models cover a variety of different training methods such as SFT, further pretrain, RLHF and multi-modality, which further validates the method proposed by the team. Robustness of large models in subsequent different training paradigms.

In addition, the figure below is the experimental results they conducted on 24 independently trained open source base models. Through their method, each independent base model is given a unique fingerprint image, which vividly demonstrates the diversity and difference of fingerprints between different large models. In the table, the similarity calculation results between these models are consistent with the differences presented in their fingerprint images.

Finally, the team further verified the uniqueness and stability of the parameter direction of the language model trained independently on a small scale. They pre-trained four GPT-NeoX-350M models from scratch using one-tenth of the Pile dataset.

These models are identical in setup, the only difference is the use of different random number seeds. It is obvious from the chart below that only the difference in random number seeds leads to significantly different model parameter directions and fingerprints, which fully illustrates the uniqueness of the independently trained language model parameter directions.

Finally, by comparing the similarity of adjacent checkpoints, they found that during the pre-training process, the parameters of the model gradually tended to be stable. They believe that this trend will be more obvious in longer training steps and larger models, which also partly explains the effectiveness of their method.

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