Evaluating Large Language Models for Phishing Detection, Self-Consistency, Faithfulness, and Explainability

TL;DR

This paper evaluates large language models for phishing detection, focusing on their accuracy, explainability, and internal consistency, and compares models like BERT, Llama, and Wizard using specialized metrics.

Contribution

It introduces a comprehensive evaluation of LLMs for phishing detection, emphasizing explainability and consistency, and applies novel metrics like CC SHAP to assess faithfulness.

Findings

Llama models show higher explanation consistency despite lower accuracy.

Wizard models achieve better classification accuracy but lower explanation alignment.

The study highlights trade-offs between accuracy and explainability in LLMs for cybersecurity.

Abstract

Phishing attacks remain one of the most prevalent and persistent cybersecurity threat with attackers continuously evolving and intensifying tactics to evade the general detection system. Despite significant advances in artificial intelligence and machine learning, faithfully reproducing the interpretable reasoning with classification and explainability that underpin phishing judgments remains challenging. Due to recent advancement in Natural Language Processing, Large Language Models (LLMs) show a promising direction and potential for improving domain specific phishing classification tasks. However, enhancing the reliability and robustness of classification models requires not only accurate predictions from LLMs but also consistent and trustworthy explanations aligning with those predictions. Therefore, a key question remains: can LLMs not only classify phishing emails accurately but also generate explanations that are reliably aligned with their predictions and internally self-consistent? To answer these questions, we have fine-tuned transformer based models, including BERT, Llama models, and Wizard, to improve domain relevance and make them more tailored to phishing specific distinctions, using Binary Sequence Classification, Contrastive Learning (CL) and Direct Preference Optimization (DPO). To that end, we examined their performance in phishing classification and explainability by applying the ConsistenCy measure based on SHAPley values (CC SHAP), which measures prediction explanation token alignment to test the model's internal faithfulness and consistency and uncover the rationale behind its predictions and reasoning. Overall, our findings show that Llama models exhibit stronger prediction explanation token alignment with higher CC SHAP scores despite lacking reliable decision making accuracy, whereas Wizard achieves better prediction accuracy but lower CC SHAP scores.