The NSA FOIA office has released the TICOM report DF-240‘Characteristics, Analysis and security of cryptographic systems’. Google drive link.
Contents of the file:
240 A - Table of contents
240 B - Analysis of Enigma cipher machine type K
240 Part 1 - Treatise on cryptography
240 Part 2 - Treatise on cryptography
240 Part 3 and 4 - Treatise on cryptography
Enjoy!