java caesar密码

我用它运行的java做了caesar密码，但是在用户输入密钥后没有加密任何东西！

这是我的代码

public class CaesarCipher { public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz"; public static String encrypt(String plainText, int shiftKey) { plainText = plainText.toLowerCase(); String cipherText = ""; for (int i = 0; i < plainText.length(); i++) { int charPosition = ALPHABET.indexOf(plainText.charAt(i)); int keyVal = (shiftKey + charPosition) % 26; char replaceVal = ALPHABET.charAt(keyVal); cipherText += replaceVal; } return cipherText; } public static String decrypt(String cipherText, int shiftKey) { cipherText = cipherText.toLowerCase(); String plainText = ""; for (int i = 0; i < cipherText.length(); i++) { int charPosition = ALPHABET.indexOf(cipherText.charAt(i)); int keyVal = (charPosition - shiftKey) % 26; if (keyVal < 0) { keyVal = ALPHABET.length() + keyVal; } char replaceVal = ALPHABET.charAt(keyVal); plainText += replaceVal; } return plainText; } public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.println("Enter the String for Encryption: "); String message = new String(); message = sc.next(); System.out.println(encrypt(message, 3)); System.out.println(decrypt(encrypt(message, 3), 3)); sc.close(); } } 

跑：

 Enter The Plain Text: Reem LA Enter The Key: 2 The Cipher Text 

Answer 1

使用indexOf效率不高……您可以对char值进行整数运算以获取其索引。

我在代码中包含了注释以解释更多，但这是我想出的。

 public class CaesarCipher { // Rotate a character k-positions public static char cipher(char c, int k) { // declare some helping constants final int alphaLength = 26; final char asciiShift = Character.isUpperCase(c) ? 'A' : 'a'; final int cipherShift = k % alphaLength; // shift down to 0..25 for a..z char shifted = (char) (c - asciiShift); // rotate the letter and handle "wrap-around" for negatives and value >= 26 shifted = (char) ((shifted + cipherShift + alphaLength) % alphaLength); // shift back up to english characters return (char) (shifted + asciiShift); } // Rotate a string k-positions public static String cipher(String s, int k) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < s.length(); i++) { sb.append(cipher(s.charAt(i), k)); } return sb.toString(); } public static void main(String[] args) { Scanner keyboard = new Scanner(System.in); String password; int key; System.out.print("Please enter a password: "); password = keyboard.nextLine(); do { System.out.print("Please enter a key between 1-25: "); key = keyboard.nextInt(); if (key < 1 || key > 25) { System.out.printf(" The key must be between 1 and 25, you entered %d.\n", key); } } while (key < 1 || key > 25); System.out.println("Password:\t" + password); String encryption = cipher(password, key); System.out.println("Encrypted:\t" + encryption); System.out.println("Decrypted:\t" + cipher(encryption, -key)); } } 

输出应该是这样的

 Please enter a password: ABCDEFGHIJKLMNOPQRSTUVWXYZ Please enter a key between 1-25: 1 Password: ABCDEFGHIJKLMNOPQRSTUVWXYZ Encrypted: BCDEFGHIJKLMNOPQRSTUVWXYZA Decrypted: ABCDEFGHIJKLMNOPQRSTUVWXYZ 

Answer 2

尝试这个：

 import java.util.*; public class CaesarCipher { public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz"; public static String encrypt(String plainText, int shiftKey) { plainText = plainText.toLowerCase(); String cipherText = ""; for (int i = 0; i < plainText.length(); i++) { char replaceVal = plainText.charAt(i); int charPosition = ALPHABET.indexOf(replaceVal); if(charPosition != -1) { int keyVal = (shiftKey + charPosition) % 26; replaceVal = ALPHABET.charAt(keyVal); } cipherText += replaceVal; } return cipherText; } public static String decrypt(String cipherText, int shiftKey) { cipherText = cipherText.toLowerCase(); String plainText = ""; for (int i = 0; i < cipherText.length(); i++) { char replaceVal = cipherText.charAt(i); int charPosition = ALPHABET.indexOf(replaceVal); if(charPosition != -1) { int keyVal = (charPosition - shiftKey) % 26; if (keyVal < 0) { keyVal = ALPHABET.length() + keyVal; } replaceVal = ALPHABET.charAt(keyVal); } plainText += replaceVal; } return plainText; } public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.println("Enter the String for Encryption: "); String message = new String(); message = sc.nextLine(); System.out.println(encrypt(message, 3)); System.out.println(decrypt(encrypt(message, 3), 3)); sc.close(); } } 

这适用于所有字母字符串......但是根据您的程序，这会将原始邮件转换为小写。 因此，这不是纯加密，因为您的程序不区分大小写。

如果您希望程序区分大小写，请执行以下程序：

 import java.util.*; public class CaesarCipher { public static final String ALPHABET_LOWER = "abcdefghijklmnopqrstuvwxyz"; public static final String ALPHABET_UPPER = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; public static String encrypt(String plainText, int shiftKey) { String cipherText = ""; for (int i = 0; i < plainText.length(); i++) { int charPosition = -1; char replaceVal; int keyVal = -1; char val = plainText.charAt(i); System.out.println(val); if(Character.isUpperCase(val)) { charPosition = ALPHABET_UPPER.indexOf(val); if(charPosition != -1) { keyVal = (shiftKey + charPosition) % 26; replaceVal = ALPHABET_UPPER.charAt(keyVal); } else { replaceVal = plainText.charAt(i); } } else { charPosition = ALPHABET_LOWER.indexOf(val); if(charPosition != -1) { keyVal = (shiftKey + charPosition) % 26; replaceVal = ALPHABET_LOWER.charAt(keyVal); } else { replaceVal = plainText.charAt(i); } } System.out.println("Cipher: "+cipherText); cipherText += replaceVal; } return cipherText; } public static String decrypt(String cipherText, int shiftKey) { String plainText = ""; for (int i = 0; i < cipherText.length(); i++) { int charPosition = -1; char replaceVal; int keyVal = -1; char val = cipherText.charAt(i); if(Character.isUpperCase(val)) { charPosition = ALPHABET_UPPER.indexOf(val); if(charPosition != -1) { keyVal = (charPosition - shiftKey) % 26; if (keyVal < 0) { keyVal = ALPHABET_UPPER.length() + keyVal; } replaceVal = ALPHABET_UPPER.charAt(keyVal); } else { replaceVal = cipherText.charAt(i); } } else { charPosition = ALPHABET_LOWER.indexOf(val); if(charPosition != -1) { keyVal = (charPosition - shiftKey) % 26; if (keyVal < 0) { keyVal = ALPHABET_LOWER.length() + keyVal; } replaceVal = ALPHABET_LOWER.charAt(keyVal); } else { replaceVal = cipherText.charAt(i); } } plainText += replaceVal; } return plainText; } public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.println("Enter the String for Encryption: "); String message = new String(); message = sc.nextLine(); System.out.println(encrypt(message, 3)); System.out.println(decrypt(encrypt(message, 3), 3)); sc.close(); } } 

希望这能给出一些想法。 祝一切顺利。

Answer 3

这可能是最简单的方法，也是最容易理解的：

 import java.util.*; public class CeaserCipher { public static void main (String [] args) { Scanner input = new Scanner(System.in); System.out.print("Type your message "); String message = input.nextLine().toUpperCase(); System.out.print("Set Encoding Key "); int key = input.nextInt() % 26; for (int i = 0; i < message.length(); i++) { char c = message.charAt(i); if (c <= 64 || c >= 91) { c += 0; } else { c += key; if (c >= 91) { c -= 26; } } System.out.print(c); } } }