Author here. After the NIST curve seed mystery was solved earlier this week, I set out to find other unexplained mystery constants in old ciphers, and had Claude Code (Opus 5.5) systematically scan for candidates and attempt to reverse-engineer their construction. One of these was RC2's 256-byte permutation table, created by Ron Rivest. It was described as having been derived from the digits of π - but exactly how seems to have remained a mystery.
Claude attempted several different approaches and eventually, drawing on a historical clue in how the MD2's substitution table was constructed, found a surprisingly simple method that reproduces all 256 entries exactly. I've shared the derivation and reproducible code. I couldn't find any evidence of an existing public answer to this, but will certainly update if one comes to light.
Author here. After the NIST curve seed mystery was solved earlier this week, I set out to find other unexplained mystery constants in old ciphers, and had Claude Code (Opus 5.5) systematically scan for candidates and attempt to reverse-engineer their construction. One of these was RC2's 256-byte permutation table, created by Ron Rivest. It was described as having been derived from the digits of π - but exactly how seems to have remained a mystery.
Claude attempted several different approaches and eventually, drawing on a historical clue in how the MD2's substitution table was constructed, found a surprisingly simple method that reproduces all 256 entries exactly. I've shared the derivation and reproducible code. I couldn't find any evidence of an existing public answer to this, but will certainly update if one comes to light.