Cryptology: The Science of Secret Codes and Cipher

The word Cryptology comes from the Greek word kryptos, which means hidden and logos, which means word. It is the branch of science that deals with secret communications. To keep communications secret, it is necessary to use a code, a cipher, or both.

A code is a system of symbols representing letters, numbers or words. For example, you could create a code that might represent the following words as:

The=01, in=02, Spain=03, mainly=04, rain=05, falls=06, Germany=07, drops=08, on=09, plain=10

The encoded message might read:

01 05 02 03 06 04 09 01 10.

When you decoded the message by replacing the number with the matching word you get:

The rain in Spain falls mainly on the plain.

Without the table showing what words go with which numbers, it would be very hard to guess the meaning of the encoded message. For this reason codes have been used for thousands of years by people to protect private messages.

Codes are not used only to protect secret information. Certain codes, like Morse Code, were developed before the radio and the telephone to make it easy to send messages great distances. The telegraph allowed a single tone, or beep, to be sent through a wire to a remote location. Morse code translates the letters of the alphabet into a series of short or long beeps. For example, an A is sent as a short beep followed by a long beep. Messages were sent letter by letter across the telegraph wire as many long and short beeps. Morse code could also be used to allow two ships to communicate through the use of blinking signal lights. Even today Morse code is still used in radio because the beeps sometimes can get through heavy static that voice communications cannot.

The table that contains the translation of the words to the code is often in the form of a book and is referred to as a codebook.

A codebook does not need to be a special book filled only with a code. Messages can be passed using any two identical books as long as they contain the words in the message. For example, a spy in country A can send a message to a spy in country B as long as they have the same copy and revision of the book. Take the code:

38-1-1, 213-27-4, 46-22-1

It is meaningless unless you know that the first three numbers represent the page, line and number of words from the left edge in the book Control of Nature by John McPhee. The first three numbers give you the first word of the coded message, the second three numbers the second word, and so on. With this information it is possible to tell that this encoded message is the first three words of:

The rain in Spain falls mainly on the plain.

The fourth word in this message points out a flaw in this system. The book Control of Nature does not contain the word Spain. Any spy would have to find an alternate wording for his message. Even the words that can be found in the book can be difficult to locate, making encoding and decoding time consuming. One way of solving this problem is to use a cipher instead of a code.

Ciphers

A cipher is a system for encoding individual letters or pairs of letters in a message. One of the simplest ciphers was said to have been used by Julius Caesar and for that reason this type of cipher still bears his name. The Caesar cipher shifts letters around. For example, every letter on the left of the equal sign below corresponds to a letter on the right:

A=C, B=D, C=E, D=F, E=G, F=H, G=I, H=J, I=K, J=L, K=M, L=N, M=O, N=P, O=Q, P=R, Q=S, R=T, S=U, T=V, U=W, V=X, W=Y, X=Z, Y=A, Z=B

We refer to the message before it gets encrypted as the plaintext. You could encrypt the plaintext:

Meet you at the corner

By substituting an O for the M, then a G for an E, another G for the E, and so on until the whole message was changed to:

OGGV AQW CV VJG EQTPGT

This is called a substitution cipher. The encoded message is nolonger readable. To make it even harder to understand, the coder can break the letters up into arbitrary groups of five or so (called code groups) with no spaces. Extra meaningless letters are filled in at the end to make the last code group the same length as the others. This hides the length of each of the words in the message. After breaking the above message up into code groups we get:

OGGVA QWCVV JGEQT PGTXY

Source: http://www.unmuseum.org

Cryptology: The Science of Secret Codes and Cipher

The word Cryptology comes from the Greek word kryptos, which means hidden and logos, which means word. It is the branch of science that deals with secret communications. To keep communications secret, it is necessary to use a code, a cipher, or both.

A code is a system of symbols representing letters, numbers or words. For example, you could create a code that might represent the following words as:

The=01, in=02, Spain=03, mainly=04, rain=05, falls=06, Germany=07, drops=08, on=09, plain=10

The encoded message might read:

01 05 02 03 06 04 09 01 10.

When you decoded the message by replacing the number with the matching word you get:

The rain in Spain falls mainly on the plain.

Without the table showing what words go with which numbers, it would be very hard to guess the meaning of the encoded message. For this reason codes have been used for thousands of years by people to protect private messages.

Codes are not used only to protect secret information. Certain codes, like Morse Code, were developed before the radio and the telephone to make it easy to send messages great distances. The telegraph allowed a single tone, or beep, to be sent through a wire to a remote location. Morse code translates the letters of the alphabet into a series of short or long beeps. For example, an A is sent as a short beep followed by a long beep. Messages were sent letter by letter across the telegraph wire as many long and short beeps. Morse code could also be used to allow two ships to communicate through the use of blinking signal lights. Even today Morse code is still used in radio because the beeps sometimes can get through heavy static that voice communications cannot.

The table that contains the translation of the words to the code is often in the form of a book and is referred to as a codebook.

A codebook does not need to be a special book filled only with a code. Messages can be passed using any two identical books as long as they contain the words in the message. For example, a spy in country A can send a message to a spy in country B as long as they have the same copy and revision of the book. Take the code:

38-1-1, 213-27-4, 46-22-1

It is meaningless unless you know that the first three numbers represent the page, line and number of words from the left edge in the book Control of Nature by John McPhee. The first three numbers give you the first word of the coded message, the second three numbers the second word, and so on. With this information it is possible to tell that this encoded message is the first three words of:

The rain in Spain falls mainly on the plain.

The fourth word in this message points out a flaw in this system. The book Control of Nature does not contain the word Spain. Any spy would have to find an alternate wording for his message. Even the words that can be found in the book can be difficult to locate, making encoding and decoding time consuming. One way of solving this problem is to use a cipher instead of a code.

Ciphers

A cipher is a system for encoding individual letters or pairs of letters in a message. One of the simplest ciphers was said to have been used by Julius Caesar and for that reason this type of cipher still bears his name. The Caesar cipher shifts letters around. For example, every letter on the left of the equal sign below corresponds to a letter on the right:

A=C, B=D, C=E, D=F, E=G, F=H, G=I, H=J, I=K, J=L, K=M, L=N, M=O, N=P, O=Q, P=R, Q=S, R=T, S=U, T=V, U=W, V=X, W=Y, X=Z, Y=A, Z=B

We refer to the message before it gets encrypted as the plaintext. You could encrypt the plaintext:

Meet you at the corner

By substituting an O for the M, then a G for an E, another G for the E, and so on until the whole message was changed to:

OGGV AQW CV VJG EQTPGT

This is called a substitution cipher. The encoded message is nolonger readable. To make it even harder to understand, the coder can break the letters up into arbitrary groups of five or so (called code groups) with no spaces. Extra meaningless letters are filled in at the end to make the last code group the same length as the others. This hides the length of each of the words in the message. After breaking the above message up into code groups we get:

OGGVA QWCVV JGEQT PGTXY

Source: http://www.unmuseum.org

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