The Enigma machine, used in several variants by the German military between the late 1920s and the end of World War II, implemented a complex electro-mechanical cipher to protect sensitive communications. Breaking the Enigma cipher at Polish Biuro Szyfrów, and the subsequent large-scale decryption of Enigma traffic at Bletchley Park, was an important factor contributing to the Allied victory[1].
Padlock icon from the Firefox web browser, meant to indicate a page has been sent in SSL or TLS-encrypted protected form. But note that a properly subverted browser might mislead a user by displaying some similar icon when a transmission is not being protected by SSL or TLS. Security is not a straightforward issue.
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