A Good Tool For Breaking Monoalphabetic Substitution Cipher

In Cryptography Substitution cipher is a method of encryption by which units of plaintext are replaced with ciphertext, according to a regular system; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by performing an inverse substitution. A monoalphabetic cipher uses fixed substitution over the entire message.

Now if you got a monoalphabetic cipher , you can break the cipher by doing some cryptanalysis. The most common way is to use frequency analysis to check the most repeated letter and compare it with the frequency analysis table to see its equal to which letter in English language. Frequency analysis table is a table of letters that shows what is the percentage of usage of each letter in English language. by repeating this method you can break the cipher.

Another way is to do brute force attack that it might took long time to broke the cipher if you don't have access to parallel computing facilities or powerful clusters.

Or you can use "Secret Code Breaker-Monoalphabetic Substitution Solver". 
download it from: http://www.secretcodebreaker.com/SCBSolvr.zip This tool use a random key to decrypt the cipher and try again by changing  1 letter of the key then it compare the result with the old result to see which one is the better one!  You might ask yourself how this tool can understand if it find the right word or not, for this problem it use a internal dictionary that it contain 52,483 word entries; each time it find two possibilities or more , it will refer to the list of word to see which one is more accurate.