Classical cryptanalysis and cipher-breaking toolkit for Julia.

• Frequency Analysis — single character, bigram, and trigram frequency distributions
• Index of Coincidence — detect mono- vs polyalphabetic ciphers
• Kasiski Examination — find repeated sequences to estimate key lengths
• Caesar Cipher — encrypt, decrypt, and automatic breaking via frequency analysis
• Vigenère Cipher — encrypt, decrypt, and automatic breaking via IoC + column analysis
• XOR Analysis — single-byte and repeating-key XOR breaking with Hamming distance key length detection
• Shannon Entropy — measure randomness of text and byte data
• Chi-Squared Test — statistical comparison against English letter frequencies
• Hamming Distance — bitwise distance between byte sequences and strings
• English Scoring — score text for English-likeness using frequency correlation

using Pkg
Pkg.add("CryptoAnalysis")

using CryptoAnalysis

# Break a Caesar cipher
plaintext, shift = break_caesar("KHOOR ZRUOG")
# ("HELLO WORLD", 3)

# Encrypt / decrypt with Vigenère
ct = vigenere_encrypt("ATTACK AT DAWN", "LEMON")
vigenere_decrypt(ct, "LEMON")

# Analyze letter frequencies
freq = frequency("The quick brown fox")

# Calculate entropy
e = entropy("some ciphertext")

# Index of coincidence
ic = index_of_coincidence("THEQUICKBROWNFOX")

# Break single-byte XOR
data = xor_encrypt(Vector{UInt8}("secret message"), UInt8[0x42])
recovered, key_byte, score = break_single_byte_xor(data)

# Chi-squared test against English
chi_squared_test("This is English text")

# Hamming distance
hamming_distance("this is a test", "wokka wokka!!!")  # 37

MIT