Substitution Cipher Decryption

The provided program helps the user with the deciphering of a substitution cipher with
the 26 letter alphabet by providing the following features
• Dynamic entering of ciphertext. Ciphertext can be modified at any point of the
process.
• Easy location of corresponding characters in the ciphertext and the substituted text
by selection.
• Fast frequency analysis for single letters, bigrams, trigrams and quadgrams (more
N -grams can be made available by adding a single line of code).
• Showing the most common letters (bi-/trigrams) in the ciphertext compared to the
most common letters (bi-/trigrams) in the British English language.
• Easy assignment and change of the substitution letters.
• Auto assignment of the 10 first letters.