caesar.h

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/**
 * @file caesar.h
 * @brief Caesar cipher encryption and decryption
 *
 * The Caesar cipher is one of the simplest encryption techniques.
 * It works by shifting each letter by a fixed number of positions
 * in the alphabet.
 */
 
#ifndef CAESAR_H
#define CAESAR_H
 
#include <stddef.h>
 
/**
 * @brief Encrypt a string using the Caesar cipher
 *
 * @param text The text to encrypt (modified in-place)
 * @param shift The number of positions to shift (0-25)
 *
 * @note Only alphabetic characters are encrypted; others remain unchanged
 * @note The shift is applied modulo 26
 */
void caesar_encrypt(char *text, int shift);
 
/**
 * @brief Decrypt a string encrypted with Caesar cipher
 *
 * @param text The text to decrypt (modified in-place)
 * @param shift The shift value used for encryption
 */
void caesar_decrypt(char *text, int shift);
 
/**
 * @brief Encrypt a single character
 *
 * @param c The character to encrypt
 * @param shift The shift value
 * @return The encrypted character
 */
char caesar_encrypt_char(char c, int shift);
 
/**
 * @brief Decrypt a single character
 *
 * @param c The character to decrypt
 * @param shift The shift value
 * @return The decrypted character
 */
char caesar_decrypt_char(char c, int shift);
 
/**
 * @brief Crack a Caesar cipher by chi-squared comparison against English
 *        letter frequencies.
 *
 * For each candidate shift 0..25, the function "decrypts" with that shift
 * and computes the chi-squared statistic between the resulting letter
 * distribution and standard English. Lowest chi-squared = best shift.
 *
 * @param text The encrypted text to analyze
 * @return The most likely shift value used (0–25)
 */
int caesar_crack(const char *text);
 
#endif /* CAESAR_H */