RC4 es un cifrado de flujo simétrico y un algoritmo de longitud de clave variable. Este algoritmo de clave simétrica se usa de manera idéntica para el cifrado y el descifrado , de modo que el flujo de datos simplemente se somete a XOR con la secuencia de claves generada. El algoritmo es en serie, ya que requiere intercambios sucesivos de entradas de estado en función de la secuencia de teclas. El algoritmo funciona en dos fases:
Algoritmo de programación clave (KSA) :
- Se utiliza para generar una array de estado aplicando una permutación mediante una clave de longitud variable que consta de 0 a 256 bytes .
- El vector de estado se identifica como S[0] , S[1]…. S[255] se inicializa con {0, 1, 2, …, 255} . La clave K[0] , K[1], …., K[255] puede tener cualquier longitud de 0 a 256 bytes y se usa para inicializar la permutación S. Cada K[I] y S[I] es un byte .
- K es una array temporal, si la longitud de la clave es de 256 bytes, cópiela en K; de lo contrario, después de copiar, las posiciones restantes de K se llenan con valores de clave repetidos hasta completarse.
S[] is permutation of 0, 1, ..., 255
key[] contains N bytes of key
for i = 0 to 255
S[i] = i
// Selects a keystream byte from
// the table
K[i] = key[i (mod N)]
i++
j = 0
for i = 0 to 255
j = (j + S[i] + K[i]) mod 256
// Swaps elements in the current
// lookup table
swap(S[i], S[j])
i = j = 0
Algoritmo de generación pseudoaleatoria (PRGA) : solía generar un byte de flujo de clave a partir de una array de vectores de estado después de una ronda más de permutación.
Keystream Generation(i := 0, j := 0 )
while Generating Output:
i = (i + 1) mod 256
j = (j + S[i]) mod 256
swap(S[i], S[j])
t = (S[i] + S[j]) mod 256
keystreamByte = S[t]
At each iteration, swap elements in table
and select keystream byte
Luego, realice XOR entre el flujo de claves generado y el texto sin formato para el cifrado.
Siga el mismo procedimiento que el anterior para el descifrado, tomando texto cifrado en lugar de texto sin formato en todas partes.
Ejemplos:
Entrada: texto sin formato = 001010010010, clave = 101001000001, n= 3
Salida:
texto cifrado = 110011100011
texto descifrado = 001010010010Entrada: texto sin formato = 1111000000001111, clave = 0101010111001010, n= 4
Salida:
texto cifrado = 0011011110100010
texto descifrado = 1111000000001111
A continuación se muestra la implementación del enfoque anterior con un resultado detallado de todos los pasos importantes involucrados:
Python3
# Python3 program for the above approach
# of RC4 algorithm
# Function for encryption
def encryption():
global key, plain_text, n
# Given text and key
plain_text = "001010010010"
key = "101001000001"
# n is the no: of bits to
# be considered at a time
n = 3
print("Plain text : ", plain_text)
print("Key : ", key)
print("n : ", n)
print(" ")
# The initial state vector array
S = [i for i in range(0, 2**n)]
print("S : ", S)
key_list = [key[i:i + n] for i in range(0, len(key), n)]
# Convert to key_stream to decimal
for i in range(len(key_list)):
key_list[i] = int(key_list[i], 2)
# Convert to plain_text to decimal
global pt
pt = [plain_text[i:i + n] for i in range(0, len(plain_text), n)]
for i in range(len(pt)):
pt[i] = int(pt[i], 2)
print("Plain text ( in array form ): ", pt)
# Making key_stream equal
# to length of state vector
diff = int(len(S)-len(key_list))
if diff != 0:
for i in range(0, diff):
key_list.append(key_list[i])
print("Key list : ", key_list)
print(" ")
# Perform the KSA algorithm
def KSA():
j = 0
N = len(S)
# Iterate over the range [0, N]
for i in range(0, N):
# Find the key
j = (j + S[i]+key_list[i]) % N
# Update S[i] and S[j]
S[i], S[j] = S[j], S[i]
print(i, " ", end ="")
# Print S
print(S)
initial_permutation_array = S
print(" ")
print("The initial permutation array is : ",
initial_permutation_array)
print("KSA iterations : ")
print(" ")
KSA()
print(" ")
# Perform PGRA algorithm
def PGRA():
N = len(S)
i = j = 0
global key_stream
key_stream = []
# Iterate over [0, length of pt]
for k in range(0, len(pt)):
i = (i + 1) % N
j = (j + S[i]) % N
# Update S[i] and S[j]
S[i], S[j] = S[j], S[i]
print(k, " ", end ="")
print(S)
t = (S[i]+S[j]) % N
key_stream.append(S[t])
# Print the key stream
print("Key stream : ", key_stream)
print(" ")
print("PGRA iterations : ")
print(" ")
PGRA()
# Performing XOR between generated
# key stream and plain text
def XOR():
global cipher_text
cipher_text = []
for i in range(len(pt)):
c = key_stream[i] ^ pt[i]
cipher_text.append(c)
XOR()
# Convert the encrypted text to
# bits form
encrypted_to_bits = ""
for i in cipher_text:
encrypted_to_bits += '0'*(n-len(bin(i)[2:]))+bin(i)[2:]
print(" ")
print("Cipher text : ", encrypted_to_bits)
encryption()
print("---------------------------------------------------------")
# Function for decryption of data
def decryption():
# The initial state vector array
S = [i for i in range(0, 2**n)]
key_list = [key[i:i + n] for i in range(0, len(key), n)]
# Convert to key_stream to decimal
for i in range(len(key_list)):
key_list[i] = int(key_list[i], 2)
# Convert to plain_text to decimal
global pt
pt = [plain_text[i:i + n] for i in range(0, len(plain_text), n)]
for i in range(len(pt)):
pt[i] = int(pt[i], 2)
# making key_stream equal
# to length of state vector
diff = int(len(S)-len(key_list))
if diff != 0:
for i in range(0, diff):
key_list.append(key_list[i])
print(" ")
# KSA algorithm
def KSA():
j = 0
N = len(S)
# Iterate over the range [0, N]
for i in range(0, N):
j = (j + S[i]+key_list[i]) % N
# Update S[i] and S[j]
S[i], S[j] = S[j], S[i]
print(i, " ", end ="")
print(S)
initial_permutation_array = S
print(" ")
print("The initial permutation array is : ",
initial_permutation_array)
print("KSA iterations : ")
print(" ")
KSA()
print(" ")
# Perform PRGA algorithm
def do_PGRA():
N = len(S)
i = j = 0
global key_stream
key_stream = []
# Iterate over the range
for k in range(0, len(pt)):
i = (i + 1) % N
j = (j + S[i]) % N
# Update S[i] and S[j]
S[i], S[j] = S[j], S[i]
print(k, " ", end ="")
print(S)
t = (S[i]+S[j]) % N
key_stream.append(S[t])
print("Key stream : ", key_stream)
print(" ")
print("PGRA iterations : ")
print(" ")
do_PGRA()
# Perform XOR between generated
# key stream and cipher text
def do_XOR():
global original_text
original_text = []
for i in range(len(cipher_text)):
p = key_stream[i] ^ cipher_text[i]
original_text.append(p)
do_XOR()
# convert the decrypted text to
# the bits form
decrypted_to_bits = ""
for i in original_text:
decrypted_to_bits += '0'*(n-len(bin(i)[2:]))+bin(i)[2:]
print(" ")
print("Decrypted text : ",
decrypted_to_bits)
# Driver Code
decryption()
Producción:
Plain text : 001010010010 Key : 101001000001 n : 3 S : [0, 1, 2, 3, 4, 5, 6, 7] Plain text ( in array form ): [1, 2, 2, 2] Key list : [5, 1, 0, 1, 5, 1, 0, 1] KSA iterations : 0 [5, 1, 2, 3, 4, 0, 6, 7] 1 [5, 7, 2, 3, 4, 0, 6, 1] 2 [5, 2, 7, 3, 4, 0, 6, 1] 3 [5, 2, 7, 0, 4, 3, 6, 1] 4 [5, 2, 7, 0, 6, 3, 4, 1] 5 [5, 2, 3, 0, 6, 7, 4, 1] 6 [5, 2, 3, 0, 6, 7, 4, 1] 7 [1, 2, 3, 0, 6, 7, 4, 5] The initial permutation array is : [1, 2, 3, 0, 6, 7, 4, 5] PGRA iterations : 0 [1, 3, 2, 0, 6, 7, 4, 5] 1 [1, 3, 6, 0, 2, 7, 4, 5] 2 [1, 3, 6, 2, 0, 7, 4, 5] 3 [1, 3, 6, 2, 0, 7, 4, 5] Key stream : [7, 1, 6, 1] Cipher text : 110011100011 --------------------------------------------------------- KSA iterations : 0 [5, 1, 2, 3, 4, 0, 6, 7] 1 [5, 7, 2, 3, 4, 0, 6, 1] 2 [5, 2, 7, 3, 4, 0, 6, 1] 3 [5, 2, 7, 0, 4, 3, 6, 1] 4 [5, 2, 7, 0, 6, 3, 4, 1] 5 [5, 2, 3, 0, 6, 7, 4, 1] 6 [5, 2, 3, 0, 6, 7, 4, 1] 7 [1, 2, 3, 0, 6, 7, 4, 5] The initial permutation array is : [1, 2, 3, 0, 6, 7, 4, 5] Key stream : [7, 1, 6, 1] PGRA iterations : 0 [1, 3, 2, 0, 6, 7, 4, 5] 1 [1, 3, 6, 0, 2, 7, 4, 5] 2 [1, 3, 6, 2, 0, 7, 4, 5] 3 [1, 3, 6, 2, 0, 7, 4, 5] Decrypted text : 001010010010
Publicación traducida automáticamente
Artículo escrito por jaimabhagwati y traducido por Barcelona Geeks. The original can be accessed here. Licence: CCBY-SA