1518
Courtesy of the NSA Poligraphique, written by German abbot Johannes Trithemius, is released two years after his death. It may be the first book about cryptology published in the Western world. He creates a square table; each row inside it has an alphabet used for disguising a message.
1778 AP Photo
George Washington's spies, known as the Culper Ring, write their discoveries about the British in invisible ink. Washington then decodes the messages via a special liquid. Arabs had used invisible ink more than a millennia earlier, in 600 A.D.
1780s Courtesy of the NSA
Thomas Jefferson is an avid cryptographer. He and James Madison create a private security code. In his writings, he conceives of a "wheel cypher." Because of this, he's called "Father of American Cryptography."
1803 AP Photo
Communicating with his deputies via a secret code, James Madison completes the Louisiana Purchase with France.
1809 to 1849 AP Photo
Cryptology enthusiast Edgar Allen Poe asks his readers to send him puzzles. In 1843, his story "The Gold Bug" tells of a secret message describing William Kidd's stash.
1856 Courtesy of the NSA
Army doctor Albert Myer, who had worked for a telegraph company, creates a means of sending messages via flags, spawning the American Signal Corps. This method is adopted during the Civil War. He also designs a special star flag, which is given to Signal Corps members who perform well in battle.
1861
During the American Civil War both Union and Confederate forces use the relatively new technology of the telegraph, invented in 1844. Both sides encrypt their telegraph messages and try to decipher those of the enemy.
1876
Republican Rutherford Hayes' slim electoral win over Democrat Samuel Tilden is sharply contested. Newspapers report that people close to Tilden used word codes via telegram to discuss buying votes.
1917
CBSWith the invention of wireless radio, people can communicate quickly over long distances. The advent of the radio intercept enables snoopers to listen in, ignoring distance and transmission lines.
1917
AP PhotoMata Hari, a spy for Germany in France and Spain, uses invisible ink and sex appeal to gather information. After her conviction in 1917, she is executed in France.
1919
The U.S. Cipher Bureau is started after World War I. It is informally known as the American Black Chamber, a reference to 17th century spying, when many European countries had back rooms, or black chambers, where mail was opened, copied and resealed. After the American bureau is closed in 1929, its founder, Herbert Yardley, writes The American Black Chamber. His aim is to bolster spy operations, but some fear the book gives away too much.
1924
In an early example of domestic surveillance, the American Signal Corps helps investigate the Teapot Dome scandal by decoding secret messages from some of the participants.
1914 to 1918
During World War I, the U.S. Army uses members of the Choctaw tribe to communicate secret information.

Find out more at: Choctaw Code Talkers of WWI.

1939 to 1945 CBS
The Army taps Hopi, Choctaw, Comanche, Kiowa, Winnebago, Seminole, Navajo and Cherokee Americans to use their languages as secret code in World War II. The Marines rely on Navajos to create and memorize a code based on the complex Navajo language. Learn more at Navajo Code Talkers.

Video Hattie Kauffman reports.
1930s
Cipher machines rely on the speed of an electrical rotor to substitute some letters of the alphabet for others. The Enigma machine, first invented in the 1920s, is bought by various nations, including Germany, Poland, Japan and the United States. Using the device, the Allies and the Axis try to encode and decipher each others' messages.
1940
Courtesy of NSA Harlem Renaissance dancer Josephine Baker flees the United States to seek a better life in the more tolerant Paris. During World War II, she also spies for the French using invisible ink on her sheet music and tucking photos into her clothes.
1942 Courtesy of NSA
The Japanese rely on a code that consists of 45,000 five-digit numbers, each representing a word or phrase. Code breaking by U.S. Commander Joseph Rochefort proves pivotal in winning the war in the Pacific. Translated Japanese codes provide the Americans with a sense of when the attack on Midway would occur.
1942
To transmit secret messages, Germans in Cairo broadcast text from the 1938 novel Rebecca. British agents were able to crack the cipher through the work of an international spy named Yvette.
Nov. 4, 1952
The National Security Agency is born with a top secret memo signed 11 days earlier by President Harry S. Truman.

Computers prove to be an important part of the operation. Since the 1930s, computers have been used to store spy information, create encryptions and quickly break codes by attempting different scenarios.

Try some NSA cryptic puzzles.

mid-1950s
The NSA proposes setting up 4,120 listening posts staffed 24 hours a day around the globe. At minimum, each would have a radio receiver; it might be housed in a van.
June, 1962
NSA listening posts monitoring airfields in Czechoslovakia hear Spanish along with the usual mix of Slavic languages. Later that summer, NSA listeners monitoring Cuba detect Russian ground controllers talking in Spanish to Cuban pilots. This information helps establish that the Soviet Union is moving missiles into Cuba.
1970s
APThe NSA is caught spying on anti-war protesters such as Jane Fonda and Dr. Benjamin Spock. In the 1960s, it recorded the conversations of civil rights leaders such as Martin Luther King. When Congress finds out, it drafts stricts laws barring the NSA from spying on Americans.
2000
The NSA and four English-speaking allies, Canada, Great Britain, Australia and New Zealand, jointly run Echelon, a secret global surveillance network. Its mission is to eavesdrop on other countries, terrorist groups and drug cartels. Echelon's computers capture almost every electronic conversation worldwide.
Nov. 2006
Former KGB agent turned Kremlin critic, Alexander Litvinenko, became sick on Nov. 1 and died Nov. 23. High doses of polonium-210 - a rare radioactive element usually manufactured in specialized nuclear facilities - were found in Litvinenko's body. In a deathbed accusation, Litvinenko blamed Russian President Vladimir Putin for his poisoning. Putin has denied it.

Sources: NSA; AP; The Puzzle Palace; Codes and Ciphers