Improbable Bigrams Expose Vulnerabilities of Incomplete Tokens in Byte-Level Tokenizers

• URL: http://arxiv.org/abs/2410.23684v1
• Date: Thu, 31 Oct 2024 07:19:44 GMT
• Title: Improbable Bigrams Expose Vulnerabilities of Incomplete Tokens in Byte-Level Tokenizers
• Authors: Eugene Jang, Kimin Lee, Jin-Woo Chung, Keuntae Park, Seungwon Shin,
• Abstract summary: Tokenization is a crucial step that bridges human-readable text with model-readable discrete tokens. Recent studies have revealed that tokenizers can be exploited to elicit unwanted model behaviors. We investigate incomplete tokens, i.e., undecodable tokens with stray bytes resulting from byte-level byte-pair encoding (BPE) tokenization.
• Score: 32.274579719726546
• License:
• Abstract: Tokenization is a crucial step that bridges human-readable text with model-readable discrete tokens. However, recent studies have revealed that tokenizers can be exploited to elicit unwanted model behaviors. In this work, we investigate incomplete tokens, i.e., undecodable tokens with stray bytes resulting from byte-level byte-pair encoding (BPE) tokenization. We hypothesize that such tokens are heavily reliant on their adjacent tokens and are fragile when paired with unfamiliar tokens. To demonstrate this vulnerability, we introduce improbable bigrams: out-of-distribution combinations of incomplete tokens designed to exploit their dependency. Our experiments show that improbable bigrams are significantly prone to hallucinatory behaviors. Surprisingly, alternative tokenizations of the same phrases result in drastically lower rates of hallucination (93% reduction in Llama3.1). We caution against the potential vulnerabilities introduced by byte-level BPE tokenizers, which may impede the development of trustworthy language models.

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