Burp Sequencer 101
Summary: PortSwigger's Dafydd Stuttard explains how Burp Sequencer tests session token randomness, converting each token to a bit-level representation and scoring each bit position by the lowest result across several statistical tests at a 1% significance level. He demonstrates with a broken linear congruential generator (lastToken * 13 + 27) that reports 49 bits of effective entropy at 1,000 tokens, 37 bits at 3,000, and 17 bits at 6,000, and recommends capturing at least 5,000 tokens.
Bottom line: A token generator that passes at 1,000 samples can fail outright by 6,000, so a quick 100-token run only catches blatantly non-random tokens and gives little assurance about the generator behind your session IDs.
Read the original at PortSwigger Research ↗
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