If one strips down the English alphabet to only lower case letters, (eliminate c

Question

If one strips down the English alphabet to only lower case letters, (eliminate capitalization, white space, and punctuation), then there are 26 letters. We know from combinatorics that there are 26 factorial possible distinct permutations of these 26 symbols, which, is approximately 3x1025 which is about 50 moles, which is approximately the number of water molecules in a glass of water. In other words, there are as many substitution ciphers that operate on the English language as there are molecules in a glass of water. The key space for substitution ciphers is HUGE, and this would lead a naive person to believe they are unbrekable. Please try to explain why substitution ciphers are not secure. (And, PLEASE be concise.) (Don't narrate your experience in using an on-line cracking tool. I'm not grading your creative writing skills.) If one strips down the English alphabet to only lower case letters, (eliminate capitalization, white space, and punctuation), then there are 26 letters. We know from combinatorics that there are 26 factorial possible distinct permutations of these 26 symbols, which, is approximately 3x1025 which is about 50 moles, which is approximately the number of water molecules in a glass of water. In other words, there are as many substitution ciphers that operate on the English language as there are molecules in a glass of water. The key space for substitution ciphers is HUGE, and this would lead a naive person to believe they are unbrekable. Please try to explain why substitution ciphers are not secure. (And, PLEASE be concise.) (Don't narrate your experience in using an on-line cracking tool. I'm not grading your creative writing skills.)

Explanation / Answer

Problem with simple substitution ciphers is that the frequencies of letters are not masked. If the enciphered message “wklv lv whvw” was intercepted, the interceptor could look at the frequencies of each letter and compare them to the frequencies of English alphabets:
'w' is used three times in the enciphered message, and l, v appear twice.
As a guess, the interceptor could line up the letters as follows:

Cipher             Plain

w                     t

l                       i

v                      s

A quick deciphering test gives the answer t?is is t?st

If the interceptor agrees that w = t and sees that the first word could decipher as t?is then it is easy for deciphering the rest of the message.

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.