Donat un missatge de text sense format i una clau numèrica xifrar/desxifrar el text donat mitjançant l'algoritme Rail Fence.
El xifratge de tanca de ferrocarril (també anomenat xifrat en zig-zag) és una forma de xifrat de transposició. Deriva el seu nom de la forma en què està codificat.
Exemples:
Encryption
Input : 'GeeksforGeeks '
Key = 3
Output : GsGsekfrek eoe
Decryption
Input : GsGsekfrek eoe
Key = 3
Output : 'GeeksforGeeks '
Encryption
Input : 'defend the east wall'
Key = 3
Output : dnhaweedtees alf tl
Decryption
Input : dnhaweedtees alf tl
Key = 3
Output : defend the east wall
Encryption
Input : 'attack at once'
Key = 2
Output : atc toctaka ne
Decryption
Input : 'atc toctaka ne'
Key = 2
Output : attack at once
Xifratge
En un xifrat de transposició, l'ordre dels alfabets es reordena per obtenir el text xifrat.
- En el xifrat de la tanca del carril, el text pla s'escriu cap avall i en diagonal sobre els rails successius d'una tanca imaginària.
- Quan arribem al rail inferior recorrem cap amunt movent-nos en diagonal després d'arribar al rail superior la direcció es torna a canviar. Així, els alfabets del missatge s'escriuen en zig-zag.
- Després d'escriure cada alfabet, les files individuals es combinen per obtenir el text xifrat.
Per exemple, si el missatge és "GeeksforGeeks" i el nombre de rails = 3, el xifrat es prepara com:
Desxifrat
Com hem vist anteriorment, el nombre de columnes en el xifratge de la tanca de ferrocarril segueix sent igual a la longitud del missatge de text sense format. I la clau correspon al nombre de rails.
llançar llançaments en java
- Per tant, la matriu de ferrocarril es pot construir en conseqüència. Un cop tinguem la matriu, podem esbrinar els punts on s'han de col·locar els textos (utilitzant la mateixa manera de moure's en diagonal cap amunt i cap avall alternativament).
- A continuació, omplim la fila del text xifrat. Després d'omplir-lo recorrem la matriu en zig-zag per obtenir el text original.
Implementació:
Sigui xifrat-text = 'GsGsekfrek eoe' i Clau = 3
- Nombre de columnes de la matriu = len(text-xifrat) = 13
- Nombre de files = clau = 3
Per tant, la matriu original serà de 3*13 ara marcant llocs amb text com a "*" que obtenim
* _ _ _ * _ _ _ * _ _ _ *
_ * _ * _ * _ * _ * _ *
_ _ * _ _ _ * _ _ _ * _
A continuació es mostra un programa per xifrar/desxifrar el missatge mitjançant l'algorisme anterior.
// C++ program to illustrate Rail Fence Cipher // Encryption and Decryption #include
// Java program to illustrate Rail Fence Cipher // Encryption and Decryption import java.util.Arrays; class RailFence { // function to encrypt a message public static String encryptRailFence(String text int key) { // create the matrix to cipher plain text // key = rows length(text) = columns char[][] rail = new char[key][text.length()]; // filling the rail matrix to distinguish filled // spaces from blank ones for (int i = 0; i < key; i++) Arrays.fill(rail[i] 'n'); boolean dirDown = false; int row = 0 col = 0; for (int i = 0; i < text.length(); i++) { // check the direction of flow // reverse the direction if we've just // filled the top or bottom rail if (row == 0 || row == key - 1) dirDown = !dirDown; // fill the corresponding alphabet rail[row][col++] = text.charAt(i); // find the next row using direction flag if (dirDown) row++; else row--; } // now we can construct the cipher using the rail // matrix StringBuilder result = new StringBuilder(); for (int i = 0; i < key; i++) for (int j = 0; j < text.length(); j++) if (rail[i][j] != 'n') result.append(rail[i][j]); return result.toString(); } // This function receives cipher-text and key // and returns the original text after decryption public static String decryptRailFence(String cipher int key) { // create the matrix to cipher plain text // key = rows length(text) = columns char[][] rail = new char[key][cipher.length()]; // filling the rail matrix to distinguish filled // spaces from blank ones for (int i = 0; i < key; i++) Arrays.fill(rail[i] 'n'); // to find the direction boolean dirDown = true; int row = 0 col = 0; // mark the places with '*' for (int i = 0; i < cipher.length(); i++) { // check the direction of flow if (row == 0) dirDown = true; if (row == key - 1) dirDown = false; // place the marker rail[row][col++] = '*'; // find the next row using direction flag if (dirDown) row++; else row--; } // now we can construct the fill the rail matrix int index = 0; for (int i = 0; i < key; i++) for (int j = 0; j < cipher.length(); j++) if (rail[i][j] == '*' && index < cipher.length()) rail[i][j] = cipher.charAt(index++); StringBuilder result = new StringBuilder(); row = 0; col = 0; for (int i = 0; i < cipher.length(); i++) { // check the direction of flow if (row == 0) dirDown = true; if (row == key - 1) dirDown = false; // place the marker if (rail[row][col] != '*') result.append(rail[row][col++]); // find the next row using direction flag if (dirDown) row++; else row--; } return result.toString(); } // driver program to check the above functions public static void main(String[] args) { // Encryption System.out.println('Encrypted Message: '); System.out.println( encryptRailFence('attack at once' 2)); System.out.println( encryptRailFence('GeeksforGeeks ' 3)); System.out.println( encryptRailFence('defend the east wall' 3)); // Now decryption of the same cipher-text System.out.println('nDecrypted Message: '); System.out.println( decryptRailFence('atc toctaka ne' 2)); System.out.println( decryptRailFence('GsGsekfrek eoe' 3)); System.out.println( decryptRailFence('dnhaweedtees alf tl' 3)); } } // This code is contributed by Jay
# Python3 program to illustrate # Rail Fence Cipher Encryption # and Decryption # function to encrypt a message def encryptRailFence(text key): # create the matrix to cipher # plain text key = rows # length(text) = columns # filling the rail matrix # to distinguish filled # spaces from blank ones rail = [['n' for i in range(len(text))] for j in range(key)] # to find the direction dir_down = False row col = 0 0 for i in range(len(text)): # check the direction of flow # reverse the direction if we've just # filled the top or bottom rail if (row == 0) or (row == key - 1): dir_down = not dir_down # fill the corresponding alphabet rail[row][col] = text[i] col += 1 # find the next row using # direction flag if dir_down: row += 1 else: row -= 1 # now we can construct the cipher # using the rail matrix result = [] for i in range(key): for j in range(len(text)): if rail[i][j] != 'n': result.append(rail[i][j]) return('' . join(result)) # This function receives cipher-text # and key and returns the original # text after decryption def decryptRailFence(cipher key): # create the matrix to cipher # plain text key = rows # length(text) = columns # filling the rail matrix to # distinguish filled spaces # from blank ones rail = [['n' for i in range(len(cipher))] for j in range(key)] # to find the direction dir_down = None row col = 0 0 # mark the places with '*' for i in range(len(cipher)): if row == 0: dir_down = True if row == key - 1: dir_down = False # place the marker rail[row][col] = '*' col += 1 # find the next row # using direction flag if dir_down: row += 1 else: row -= 1 # now we can construct the # fill the rail matrix index = 0 for i in range(key): for j in range(len(cipher)): if ((rail[i][j] == '*') and (index < len(cipher))): rail[i][j] = cipher[index] index += 1 # now read the matrix in # zig-zag manner to construct # the resultant text result = [] row col = 0 0 for i in range(len(cipher)): # check the direction of flow if row == 0: dir_down = True if row == key-1: dir_down = False # place the marker if (rail[row][col] != '*'): result.append(rail[row][col]) col += 1 # find the next row using # direction flag if dir_down: row += 1 else: row -= 1 return(''.join(result)) # Driver code if __name__ == '__main__': print(encryptRailFence('attack at once' 2)) print(encryptRailFence('GeeksforGeeks ' 3)) print(encryptRailFence('defend the east wall' 3)) # Now decryption of the # same cipher-text print(decryptRailFence('GsGsekfrek eoe' 3)) print(decryptRailFence('atc toctaka ne' 2)) print(decryptRailFence('dnhaweedtees alf tl' 3)) # This code is contributed # by Pratik Somwanshi
using System; class GFG_RailFence { // function to encrypt a message public static string EncryptRailFence(string text int key) { // create the matrix to cipher plain text // key = rows length(text) = columns char[] rail = new char[key text.Length]; // filling the rail matrix to distinguish filled // spaces from blank ones for (int i = 0; i < key; i++) for (int j = 0; j < text.Length; j++) rail[i j] = 'n'; bool dirDown = false; int row = 0 col = 0; for (int i = 0; i < text.Length; i++) { // check the direction of flow // reverse the direction if we've just // filled the top or bottom rail if (row == 0 || row == key - 1) dirDown = !dirDown; // fill the corresponding alphabet rail[row col++] = text[i]; // find the next row using direction flag if (dirDown) row++; else row--; } // now we can construct the cipher using the rail // matrix string result = ''; for (int i = 0; i < key; i++) for (int j = 0; j < text.Length; j++) if (rail[i j] != 'n') result += rail[i j]; return result; } // This function receives cipher-text and key // and returns the original text after decryption public static string DecryptRailFence(string cipher int key) { // create the matrix to cipher plain text // key = rows length(text) = columns // create the matrix to cipher plain text // key = rows length(text) = columns char[] rail = new char[key cipher.Length]; // filling the rail matrix to distinguish filled // spaces from blank ones for (int i = 0; i < key; i++) for (int j = 0; j < cipher.Length; j++) rail[i j] = 'n'; // to find the direction bool dirDown = true; int row = 0 col = 0; // mark the places with '*' for (int i = 0; i < cipher.Length; i++) { // check the direction of flow if (row == 0) dirDown = true; if (row == key - 1) dirDown = false; // place the marker rail[row col++] = '*'; // find the next row using direction flag if (dirDown) row++; else row--; } // now we can construct the fill the rail matrix int index = 0; for (int i = 0; i < key; i++) for (int j = 0; j < cipher.Length; j++) if (rail[i j] == '*' && index < cipher.Length) rail[i j] = cipher[index++]; // create the result string string result = ''; row = 0; col = 0; // iterate through the rail matrix for (int i = 0; i < cipher.Length; i++) { // check the direction of flow if (row == 0) dirDown = true; if (row == key - 1) dirDown = false; // place the marker if (rail[row col] != '*') result += rail[row col++]; // find the next row using direction flag if (dirDown) row++; else row--; } return result; } // driver program to check the above functions public static void Main() { // Encryption Console.WriteLine('Encrypted Message: '); Console.WriteLine(EncryptRailFence('attack at once' 2)); Console.WriteLine( EncryptRailFence('GeeksforGeeks ' 3)); Console.WriteLine( EncryptRailFence('defend the east wall' 3)); // Now decryption of the same cipher-text Console.WriteLine('nDecrypted Message: '); Console.WriteLine( DecryptRailFence('atc toctaka ne' 2)); Console.WriteLine( DecryptRailFence('GsGsekfrek eoe' 3)); Console.WriteLine( DecryptRailFence('dnhaweedtees alf tl' 3)); } }
// function to encrypt a message function encryptRailFence(text key) { // create the matrix to cipher plain text // key = rows text.length = columns let rail = new Array(key).fill().map(() => new Array(text.length).fill('n')); // filling the rail matrix to distinguish filled // spaces from blank ones let dir_down = false; let row = 0 col = 0; for (let i = 0; i < text.length; i++) { // check the direction of flow // reverse the direction if we've just // filled the top or bottom rail if (row == 0 || row == key - 1) dir_down = !dir_down; // fill the corresponding alphabet rail[row][col++] = text[i]; // find the next row using direction flag dir_down ? row++ : row--; } // now we can construct the cipher using the rail matrix let result = ''; for (let i = 0; i < key; i++) for (let j = 0; j < text.length; j++) if (rail[i][j] != 'n') result += rail[i][j]; return result; } // function to decrypt a message function decryptRailFence(cipher key) { // create the matrix to cipher plain text // key = rows text.length = columns let rail = new Array(key).fill().map(() => new Array(cipher.length).fill('n')); // filling the rail matrix to mark the places with '*' let dir_down = false; let row = 0 col = 0; for (let i = 0; i < cipher.length; i++) { // check the direction of flow if (row == 0) dir_down = true; if (row == key - 1) dir_down = false; // place the marker rail[row][col++] = '*'; // find the next row using direction flag dir_down ? row++ : row--; } // now we can construct the rail matrix by filling the marked places with cipher text let index = 0; for (let i = 0; i < key; i++) for (let j = 0; j < cipher.length; j++) if (rail[i][j] == '*' && index < cipher.length) rail[i][j] = cipher[index++]; // now read the matrix in zig-zag manner to construct the resultant text let result = ''; row = 0 col = 0; for (let i = 0; i < cipher.length; i++) { // check the direction of flow if (row == 0) dir_down = true; if (row == key - 1) dir_down = false; // place the marker if (rail[row][col] != '*') result += rail[row][col++]; // find the next row using direction flag dir_down ? row++ : row--; } return result; } // driver program to check the above functions // Encryption console.log(encryptRailFence('attack at once' 2)); console.log(encryptRailFence('GeeksforGeeks' 3)); console.log(encryptRailFence('defend the east wall' 3)); // Now decryption of the same cipher-text console.log(decryptRailFence('GsGsekfrek eoe' 3)); console.log(decryptRailFence('atc toctaka ne' 2)); console.log(decryptRailFence('dnhaweedtees alf tl' 3));
Sortida
atc toctaka ne GsGsekfrek eoe dnhaweedtees alf tl GeeksforGeeks attack at once defend the east wall
Complexitat temporal: O (fila * col.)
Espai auxiliar: O (fila * col.)
Referències:
https://en.wikipedia.org/wiki/Rail_fence_cipher
Aquest article és contribuït per Ashutosh Kumar