Twenty or so years' experience in cryptology having begun as a number theorist. I've developed understanding of most topics from Caesar ciphers to quantum information. I'm best at theory and standards, but less strong on implementations and libraries.
Cryptography
Q&A for software developers, mathematicians and others interested in cryptography
Puzzling
Q&A for those who create, solve, and study puzzles
History of Science and Mathematics
Q&A for people interested in the history and origins of science and mathematics
Mathematics
Q&A for people studying math at any level and professionals in related fields
Quantum Computing
Q&A for engineers, scientists, programmers, and computing professionals interested in quantum computing
Information Security
Q&A for information security professionals
Stack Overflow
Q&A for professional and enthusiast programmers
Meta Stack Exchange
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts