Interactive Hands-on Exercises
Security Engineering Labs
Apply theoretical cryptographic and architectural principles from Modules 1–6 in interactive simulations.
Module 3: Caesar Shift & Frequency Analysis Cryptanalysis
Demonstrates why monoalphabetic substitution ciphers fail against frequency analysis, as discovered by 9th-century mathematician Al-Kindi.
Caesar Shift Key (k = 3)A ➔ D
Shift 1Shift 13 (ROT13)Shift 25
FBEHUVHFXULWB LV WKH SURWHFWLRQ RI FRPSXWLQJ VBVWHPV DQG GDWD DJDLQVW DGYHUVDULDO DWWDFNV
Cryptographic Vulnerability
Notice how shifting letters does not change the frequency distribution; it merely shifts the distribution histogram along the alphabet by k=3 positions.
Top Ciphertext Frequencies vs Standard English
Sorted by occurrenceLetter 'D'10 hits (12.8%) • Expected Eng: 4.3%
Letter 'W'10 hits (12.8%) • Expected Eng: 2.4%
Letter 'V'8 hits (10.3%) • Expected Eng: 1%
Letter 'H'6 hits (7.7%) • Expected Eng: 6.1%
Letter 'L'6 hits (7.7%) • Expected Eng: 4%
Letter 'F'5 hits (6.4%) • Expected Eng: 2.2%
Letter 'U'5 hits (6.4%) • Expected Eng: 2.8%
Letter 'Q'4 hits (5.1%) • Expected Eng: 0.1%
Letter 'R'4 hits (5.1%) • Expected Eng: 6%
Letter 'B'3 hits (3.8%) • Expected Eng: 1.5%
How Cryptanalysts Crack This:
The tallest bar in English is almost always E (12.7%), followed by T, A, O, I, N. By matching the tallest bar in your ciphertext to 'E', the key k is revealed immediately!