DO NOT TRY THIS AT HOME : Rotteneggs.com text files and message bases are for INFORMATIONAL PURPOSES ONLY. DO NOT undertake any project based upon any information obtained from this or any other web site.We are not responsible for, nor do we assume any liability for, damages resulting from the use of any information on this site.
(140 votes) Published: Jun 18, 2006 2:04 p.m. In 2 Favorites Lists Viewed 872 times
Deciphering ciphers can be tricky work. Frequency Analysis is a method of decrypting ciphers based on the fact that some letters are used more often than others in the English language.
Before getting into this document too far, it is important to confirm the difference between a cipher and a code. Ciphers and codes both use replacements, but on different levels. In a cipher, replacement is made on the individual letters, meaning that cipher letter ‘R’ translated could be ‘E’ in plain text. In a code, words or phrases are replaced by different words or phrases. A code is somewhat like a different language; the word ‘livre’ in French means ‘book’ in English.
When you are going to decrypt a cipher, it is helpful to know the principles behind a few basic ciphers. One of the simplest ciphers is the Space Cipher. In the Space cipher, the only step is to change the places of the spaces in your message. Example:
USE PASSWORD H7S01Y TO ACCESS DATABASE
To
USE P AS SWORD H7S 01Y O ACC ESSDA TA BASE
Another simple cipher is Backward Cipher. In this cipher, the first and last letters are switched, then the 2nd and 2nd to last are switched, and so on. In other words, the text is written backwards. Example:
MEET ME AT THE PARK IN 15 MINUTES
To
SETUNIM 51 NI KRAP EHT TA EM TEEM
The Caesar cipher is a common cipher. A list of the letters A…Z is printed. A shift number x is decided, and a key is created from it by writing another list of the alphabet above the first and shifting the letters x to the right. Cipher letters that go past the end of the top row are moved to the beginning of the cipher row.
ABCDEFGHIJKLMNOPQRSTUVWXYZ
Shift by 3 to make the key
X Y Z A B C D E F G H I J K L M N O P Q R S T U V W
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
The top row is cipher text, and the bottom row is the plaintext. The text is converted to cipher letter by letter. The enciphered version of each letter is the letter directly above the plaintext letter. Example using above key:
WHY IS THE SKY BLUE
To
TEV FP QEB PHV YIRB
With this basic knowledge of encryption, it is possible to apply the ideas inversely to decrypt ciphers. A logical place to start decrypting a text is to look for one-letter words. These generally will translate into ‘A’ or ‘I’, which are the only one-letter words in the English language. Next count the occurrence of each letter in a cipher and compare the results with a letter frequency table. Cryptographers who have empirically assessed documents and words have developed charts, such as the one below. Based on this data, it is possible to make educated guesses on which cipher letters stand for which plaintext letters. There are also tables, which tell the frequency of commonly occurring first and last letters in words.
“It is known that in a text of 1000 letters of various English words occur with about the following relative frequencies:”(trincoll)
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
73 9 30 44 130 28 16 35 74 2 3 35 25 78 74 27 3 77 63 93 27 13 16 5 19 1
Other tables show frequency of various blends, diagraphs, and vowels. Common pairs are consonants TH and vowels EA. Others are OF, TO, IN, IT, IS, BE, AS, AT, SO, WE, HE, BY, OR, ON, DO, IF, ME, MY, UP. Common pairs of repeated letters are SS, EE, TT, FF, LL, MM and OO. Common triplets of text are THE, EST, FOR, AND, HIS, ENT or THA. (richkni) Using this information, it is possible to decrypt the following text:
AOL IYHPU PZ H DVUKLYMBS VYNHU. PA ZAHYAZ DVYRPUN AOL TVTLUA FVB NLA BW PU AOL TVYUPUN HUK KVLZ UVA ZAVW BUAPS FVB NLA AV ZJOVVS.
It is a Caesar encryption with a shift of 7. The resulting text after decrypting reads:
THE BRAIN IS A WONDERFUL ORGAN. IT STARTS WORKING THE MOMENT YOU GET UP IN THE MORNING AND DOES NOT STOP UNTIL YOU GET TO SCHOOL.
Using this basic understanding, it is possible to encrypt/decrypt basic messages. Also, searching the web or a local library for ‘Encryption’, ‘Codes’, or ‘Ciphers’ may turn up some interesting results on this subject. Good luck, try to learn as mutch as you can..Computers are the the new age
Jun 18, 2006 5:20 pm - My website has to have some security holes because the system on my website was written by me, from registriation to the loging system.
Edit Page
Message scripz
Add Comment
Add to Favorites
Email to Friend
