Secret everywhere

Cryptology is widely applied in multifarious aspects in our life: From business, government to even game, private events.

For example, it is familiar to us that most online games will require you to create a password to access to the game. But more interesting, some interactive games could let yourself set a password so that the person who are told about the password by you can access the game, other people can not access. It help people to reserve place in games.

As for private events, I remembered that when I was a child, I wrote a cipher letter to my friend just for fun. It looks a little bit childish now, but we enjoyed it very well. We felt a little bit glory that nobody else know what we talked about. It is beyond keeping secrets.

Have you created such cipher letter since you were born?

codemakers vs codebreakers

For thousands of years, the battle between code makers and code breakers never stop. After reading a lot of information about cryptology, a question flashing to my mind: who is the winner during the evolution of codes?

From some people's point of views, code makers stand at the dominant position than code breakers. Considering the first secret message created by someone, no body apart from the sender and intended recipient knew about the contents of the message. This message would at very high level of security because few people touched cryptology in that time. This situation leaded to the superiority for code makers to protect communication.

However, with accelerated development of cryptology, an increasing number of people have knowlege about cryptology. Code makers lose their advantage in cryptology because some people break their cryptoloty and disclose the cipher text, most important, key and principles. As a result, everyone who know the approach to compile the message and it utterly damage the security.

"The ongoing battle between code makers and code breakers has inspired a whole series of remarkable scientific breakthroughs." When the code breakers decipher the codes, the code makers will try their best to create a new one. So, it is not difficult to understand during the codes history, people sometimes conceal the fact that they have already broken the cipher text to prevent enemies from creating new cipher method.

So, historically, code breakers seem like winners, because no matter how unbreakable the cryptology is, eventually, it will be broken by code breakers.

I just wonder whether or not there is a code that has not been cracked so far.

Mexican army cipher disk

Mexican army cipher disk belongs to monoalphabetic cipher, it uses two digits to represent one letter. Above picture shows that there are four different cipher rows to compile letter.

For example, if we like to cipher " College", it can be represented to:

17032626192119 or,

64762697196890 etc,

A plaintext letter can be represented by several symbols, but each symbol can only represent one letter. As a result, it is not at high level of security. But I think it is interesting.

MD5

MD5 means Message-Digest Algorithm 5, invented by Ronald L. Rivest. It develops from MD4、MD3、MD2. MD5 is not used for compiling the cipher and making cipher enigmatical.It is a hash arithmetic and is used for prevent to alter the original text by comparing information summary. MD5 ciphered the byte string of any length to a fixed length interger (usually length in 16 to 32 digits). During the cipher process, some data information will be filtrated. Therefore, it is impossible to draw original text by inversely calculate the ciphered text.

For example, if you sign up to a bbs, set the password "qiuyu21". Through the MD5 process, this password will change to"287F1E255D930496EE01037339CS978D". When you click "submit", the server's database will record the calculation result "287F1E255D930496EE01037339CS978D" rather than your original password "qiuyu21". As a result, when you log in the bbs next time, server will still translate your password typed " qiuyu21" to the MD5 calculation result. After checkout, if the result matches the data in database, you can successfully log in.

What is the advantage of MD5? Well, If a hacker breaks the database, he can not use the MD5 result to log in. However, if database record the original password, once a hacker break the database, he or she could get all passwords and log in sucessfully in any other's user name.

MD5 is still in high level of security in nowadays society.

number cipher

I found a new method to compile cipher just using simple numbers.

If we need to cipher 26 letters, the simple way is to transfer the letters to numbers. For example, 1 represent A, 2 represent B and so on. If we want to cipher "number" use binary conversion, it will change to "1110 10101 1101 10 101 10010 1111 1110 101". If we use decimal conversion, the cipher message is "14 21 13 2 5 18 15 14 5"

Besides, we can use reverse to increase difficulty to decipher. For example, the plaintext is "This is a test." If we reverse the whole sentence, the cipher message will be :"tset a si siht." If we reverse every word, the cipher message turns to:"siht si a tset." To improve the cipher, we could also add the number cipher method no matter it is binary conversion or decimal conversion. You can have a try!~

about cipher disk

Because of my carelessness, I lost my cipher disk. As a result, I made a new one. The picture on the left shows my finished product.

During the process I made the cipher disk. I have some suggestions for you if you are interested in making a new one by you own.

Frist, you should use compasses to draw two circles with different diameter.

Second, after you cut the circle, you need to overlay the smaller one on the bigger one snapping to the same center of circle.

Then, you should use rulers with pass through the center of circle and make several lineations with the same angle intervals.

Last, you could find something like clip to connect two disks. Done!

Besides, I found some questions that why Alberti cipher disk does not include the whole 26 letters? Whether we could add another disk to make the cipher reach higher level of security?

The wide use of cryptology

It is widely believed that people focus on keeping privacy secure a lot. As a result, cryptology is popularly used by people no matter in which country or at what time.

Take China as an example, in ancient times, people use flames smoke signals to pass the war news. And then, a people named Gongliang Zeng collected the most common combat situations and compiled them to numbers. Before the General expedited, the general and Military chain of command would reach an agreement about a piece of poem with many words. If something happened in the battle, general would search the combat situations number and choose the word which has the same number in the poem. Then he wrote down the word and sent a soldier to pass the information.

For instance, if the combat situation is numbered 4, so the 4th word in the poem is the key to pass the information.

Cryptology is not far away from us. In recent days, for example, we need to use password plate to open our mailbox in Dickinson College. It maybe a little bit inconvenient, however, it is necessary for us to protect our secret.

Alberti Cipher Disk~

With the accelerated development of the cryptology, a growing number of people knockled down to study to improve the encryption technology.

Due to the disadvantages of monoalphabetic cipher that could be easily deciphered by analyzing the frequency of letters, priority is to create a new cipher with a higher level of security.

Then, came with polyalphabetic cipher.

One of the representative polyalphabetic ciphers machine is Alberti Cipher Disk.

Alberti Cipher Disk was the first simple substitution cipher machine ever made invented by an Indian man, Alberti.

This machine consists of two concentric disks with different letters and numbers on them, and attached by a common pin.

People spin the disk to make various substitution cipher alphabets, which means the same letter can be represented by distinct symbols.

The most crucial decipher key of this technology is the index agreed by cipher sender and intend recipient.

This technology speeded up the time needed to cipher and decipher codes as well as disturbed the analyze of letter frequency.

I try using this method to create a encoded sentences which selected from a song. Hope you can decipher it!

Note: Index=R Some missing letters in the disk is skipped in the encode message.

Encoded message: Y A V Z O K Y G A A S N Z V K F Y P O D B Y S S P S S P S Q M Z G A S A H O L H K Y M Z R F Z C P R X C Z C K X N C.

Look forward for your decipher message!