The election of 1928 brought Herbert Hoover to the presidency, with Henry Stimson as his Secretary of State. Stimson was one of the towering figures in foreign and defense policy in the first half of the Twentieth Century (he also later served in Franklin Roosevelt's administration as Secretary of War).
Stimson made a decision to eliminate the Cipher Bureau. The decision likely was based on budget considerations, but it has come down to us as based on the need for acting in good faith in international relations. Whatever the reason for terminating the Cipher Bureau, when he did so Stimson spoke the single most famous sentence ever uttered about codes and ciphers:
"Gentlemen do not read other gentlemen's mail."