While Claude Shannon was working on cryptography during the war, he worked out the key principles of information theory. Wikipedia (https://en.wikipedia.org/wiki/Claude_Shannon#Wartime_research) explains how these ideas were gradually published after the war:

At the close of the war, he prepared a classified memorandum for Bell Telephone Labs entitled "A Mathematical Theory of Cryptography", dated September 1945. A declassified version of this paper was published in 1949 as "Communication Theory of Secrecy Systems" in the Bell System Technical Journal. This paper incorporated many of the concepts and mathematical formulations that also appeared in his "A Mathematical Theory of Communication" [1948]. Shannon said that his wartime insights into communication theory and cryptography developed simultaneously and that "they were so close together you couldn’t separate them".[20] In a footnote near the beginning of the classified report, Shannon announced his intention to "develop these results … in a forthcoming memorandum on the transmission of information."[21]