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A comment on Ask HN: Generate LLM hallucination to detect students cheating. Parent comment

Re:Ask HN: Generate LLM hallucination to detect students che... by virgilp on Wednesday May 21, 2025 @06:36AM (#44050041)
I managed to get Perplexity to hallucinate, which was rather hard :) - but this is not a question that acts as a very good "template".

The question is "Is this JWT token valid or is it expired/ not valid yet? eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNzQ3ODIzNDc1LCJleHAiOjE3NDc4MjM0Nzh9.4PsZBVIRPEEQr1kmQUGejASUw0OgV1lcRot4PUFgAF0"

The answer was in some ways way better than I expected, but it got it wrong when comparing the current date/time with the "exp" datetime. Got the expiration date confidently wrong:

```

    iat (issued at): 1747823475 (Unix time)

    exp (expiration): 1747823478 (Unix time)
Token Validity Check

    The current date and time is May 21, 2025, 1:32 PM EEST, which is Unix time 1747817520.

    The token's exp value is 1747823478, which is May 21, 2025, 3:11:18 PM EEST.
Conclusion:

    The token is not expired; it will expire on May 21, 2025, at 3:11:18 PM EEST.

    The token is already valid (the iat is in the past, and the current time is before exp).
Therefore, the JWT token is currently valid and not expired or not-yet-valid.

```

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Re:Ask HN: Generate LLM hallucination to detect students che... by Filligree on Wednesday May 21, 2025 @06:39AM (#44050055)
At that point I think we can talk about “mistakes” rather than “hallucinations”.
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Re:Ask HN: Generate LLM hallucination to detect students che... by virgilp on Wednesday May 21, 2025 @06:55AM (#44050148)
On one hand, yes; on the other - a human that can produce that level of details in the output would notice that iat & exp are extremely close & the token is very unlikely to be valid. Also, you don't produce an exact number for "now" without being able to compare it correctly with iat & exp (the timestamp it stated as "now" is actually less than iat!)
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