A Partial Decryption of Kryptos K4: Identifying Multi-Key Vigenère Structure with Rotor-Based Key Rotation

Kryptos K4 has remained unsolved for over 35 years despite sustained efforts by professional cryptographers and intelligence analysts. This paper documents an independent cryptanalytic effort that identifies a previously unrecognized structural feature: double-letter positions marking transitions between distinct Vigenère keys. Using known plaintext-ciphertext pairs confirmed by sculptor Jim Sanborn (EAST, BERLIN, CLOCK, NORTHEAST), the analysis derives multiple encryption keys and demonstrates that K4 employs a multi-key system rather than a single Vigenère cipher. The structure resembles rotor-based encryption machines such as the German Enigma, with keys rotating at delimiter positions. Key findings: Positions 21–83 (excluding 49–63) decrypt to semantically coherent English Six distinct keys are derived and mathematically verified The standard alphabet (A=0...Z=25) produces valid decryptions; the Kryptos alphabet may be a misdirection The unresolved span (49–63) may represent a middle-rotor turnover or K5 bleed The paper includes full mathematical verification, testable predictions, and discussion of the Enigma hypothesis. Original research conducted April 19–22, 2025; formalized February 2026.