You can begin exploring your interest in this field by joining groups involved with cryptography, such as the American Cryptogram Association (ACA), and reading their journals, such as the ACA's The Cryptogram. Learn how to do some computer programming. This will give you experience working with codes and computers. Visit Codeacademy (https://www.codecademy.com), edX (https://www.edx.org), Coursera (https://www.coursera.org), and Khan Academy (https://www.khanacademy.org), where you can learn how to code for free. Additionally, the Khan Academy offers a free online class, Journey Into Cryptography, at https://www.khanacademy.org/computing/computer-science/cryptography.

If your high school has math and computer science clubs, join them.

Participate in summer programs offered by colleges and universities and intelligence agencies. For example, the National Security Agency offers a Gifted and Talented Program for high school seniors who are interested in engineering, math, and science. Students who are accepted into the program work 40 hours per week for 10 to 12 weeks during the summer following their senior year of high school. Visit https://www.intelligencecareers.gov/icstudents.html?Agency=NSA to learn more about this and other NSA programs. 

You may also want to check out Reserve Officers Training Corps (ROTC) programs offered by the different branches of military service. These may provide some introduction to cryptographic techniques.

Visit the National Cryptologic Museum (https://www.nsa.gov/about/cryptologic-heritage/museum) in Ft. Meade, Maryland. It features thousands of cryptology-related artifacts, including commercial code books, declassified NSA documents, and transcribed oral histories. 

The American Cryptogram Association offers a variety of free cryptographic-related downloads at https://www.cryptogram.org/resource-area.

Cryptography has always been an important tool for the U.S. government to use in providing security and protection to its citizens, particularly during wars. The significance of sending and receiving coded messages has been enhanced since the terrorist attacks on the United States on September 11, 2001. The leading government agency dedicated to cryptanalysis is the NSA, which is administered by the Department of Defense. The Central Security Service (CSS), a partner with NSA, is responsible for the cryptanalysis activities in all branches of the U.S. military (army, air force, navy, and marines). 

Cryptanalysts use a variety of skills and tools to do their work. They draw on their knowledge of mathematics, languages, engineering, and computer programming, to determine the basic rules or principles governing an unknown code. Once the basic principles at work in a code are understood, the code can be "broken" or deciphered. Cryptanalysts are familiar with cryptographic software, radio equipment, computer equipment, surveillance devices, and other technologies used by the defense and intelligence communities.

Cryptographic technicians working in the military have a key role in protecting our armed forces and helping them complete successful missions. When military personnel are far from home on a training mission or at war, they rely on messages sent from headquarters to update them on world events and give them orders. In the air force, for example, to send information to a flight crew on a 20-hour training mission, secret signals must be transmitted via radio waves, using HF (high frequency), UHF (ultrahigh frequency), or SATCOM (satellite communications). Because other nations have access to these same frequencies, the messages must be in code to protect national military secrets. In the plane, the cryptographic technician decodes the message, which might alter a set of targets to hit, or instruct the pilot to land at a different air force base.

Cryptographic technicians working for agencies in the intelligence community, such as the NSA, may be involved with decoding information that intelligence workers have intercepted from groups or governments unfriendly to the United States. And, like those technicians working in the military, they may also create codes to use for sending sensitive information to U.S. intelligence workers and our allies around the world.

In the private sector, cryptoanalysts working for the banking industry or any other industry requiring computer security must prevent unauthorized access to protect the accounts or data in the files. For instance, when funds are being transferred from one bank to another, the transfer message is usually sent by computer. To prevent unauthorized transfers, the banks send the message in code, along with some means of authenticating the transaction.

In order to code and send secret messages, cryptographic technicians first select the particular code that they should use for the message. Then they set up their machine to translate the message into that code, and they type the message into the machine. The machine converts the message into code form in a process known as encryption. After the message is encrypted, the technicians send the message to a receiver via telephone lines, satellites, or other kinds of communication links.

When receiving a message in a known code, cryptographic technicians feed the incoming transmission into a decoding machine (or decoding software) and take the resulting message to its intended receiver. If a message appears to have been improperly coded, technicians may try to straighten out the message using special decoding procedures and equipment, or they may request that the message be sent again.

To send and receive coded messages, cryptographic technicians may develop their own cryptographic software programs, use teletypewriters, or operate radio transmitters and receivers.