Java/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java at master · TheAlgorithms/Java · GitHub

Name: Java/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java at master · TheAlgorithms/Java · GitHub
Rating: 4.4 (1001 reviews)
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packagecom.thealgorithms.ciphers;

publicclassPlayfairCipher {

privatechar[][] matrix;
privateStringkey;

publicPlayfairCipher(Stringkey) {
this.key = key;
generateMatrix();
 }

publicStringencrypt(Stringplaintext) {
plaintext = prepareText(plaintext.replace("J", "I"));
StringBuilderciphertext = newStringBuilder();
for (inti = 0; i < plaintext.length(); i += 2) {
charchar1 = plaintext.charAt(i);
charchar2 = plaintext.charAt(i + 1);
int[] pos1 = findPosition(char1);
int[] pos2 = findPosition(char2);
introw1 = pos1[0];
intcol1 = pos1[1];
introw2 = pos2[0];
intcol2 = pos2[1];
if (row1 == row2) {
ciphertext.append(matrix[row1][(col1 + 1) % 5]);
ciphertext.append(matrix[row2][(col2 + 1) % 5]);
 } elseif (col1 == col2) {
ciphertext.append(matrix[(row1 + 1) % 5][col1]);
ciphertext.append(matrix[(row2 + 1) % 5][col2]);
 } else {
ciphertext.append(matrix[row1][col2]);
ciphertext.append(matrix[row2][col1]);
 }
 }
returnciphertext.toString();
 }

publicStringdecrypt(Stringciphertext) {
StringBuilderplaintext = newStringBuilder();
for (inti = 0; i < ciphertext.length(); i += 2) {
charchar1 = ciphertext.charAt(i);
charchar2 = ciphertext.charAt(i + 1);
int[] pos1 = findPosition(char1);
int[] pos2 = findPosition(char2);
introw1 = pos1[0];
intcol1 = pos1[1];
introw2 = pos2[0];
intcol2 = pos2[1];
if (row1 == row2) {
plaintext.append(matrix[row1][(col1 + 4) % 5]);
plaintext.append(matrix[row2][(col2 + 4) % 5]);
 } elseif (col1 == col2) {
plaintext.append(matrix[(row1 + 4) % 5][col1]);
plaintext.append(matrix[(row2 + 4) % 5][col2]);
 } else {
plaintext.append(matrix[row1][col2]);
plaintext.append(matrix[row2][col1]);
 }
 }
returnplaintext.toString();
 }

privatevoidgenerateMatrix() {
StringkeyWithoutDuplicates = removeDuplicateChars(key + "ABCDEFGHIKLMNOPQRSTUVWXYZ");
matrix = newchar[5][5];
intindex = 0;
for (inti = 0; i < 5; i++) {
for (intj = 0; j < 5; j++) {
matrix[i][j] = keyWithoutDuplicates.charAt(index);
index++;
 }
 }
 }

privateStringremoveDuplicateChars(Stringstr) {
StringBuilderresult = newStringBuilder();
for (inti = 0; i < str.length(); i++) {
if (result.indexOf(String.valueOf(str.charAt(i))) == -1) {
result.append(str.charAt(i));
 }
 }
returnresult.toString();
 }

privateStringprepareText(Stringtext) {
text = text.toUpperCase().replaceAll("[^A-Z]", "");
StringBuilderpreparedText = newStringBuilder();
charprevChar = '\0';
for (charc : text.toCharArray()) {
if (c != prevChar) {
preparedText.append(c);
prevChar = c;
 } else {
preparedText.append('X').append(c);
prevChar = '\0';
 }
 }
if (preparedText.length() % 2 != 0) {
preparedText.append('X');
 }
returnpreparedText.toString();
 }

privateint[] findPosition(charc) {
int[] pos = newint[2];
for (inti = 0; i < 5; i++) {
for (intj = 0; j < 5; j++) {
if (matrix[i][j] == c) {
pos[0] = i;
pos[1] = j;
returnpos;
 }
 }
 }
returnpos;
 }

publicvoidprintMatrix() {
System.out.println("\nPlayfair Cipher Matrix:");
for (inti = 0; i < 5; i++) {
for (intj = 0; j < 5; j++) {
System.out.print(matrix[i][j] + " ");
 }
System.out.println();
 }
 }
}