# skipjack.py class SkipJack: def __init__(self): # F is an 8-bit S-box self.F = [] self.defineF() # w1, w2, w3, w4 are 16-bit integers self.w1 = 0 self.w2 = 0 self.w3 = 0 self.w4 = 0 # plaintext is a 64-bit integer # key is a list of 10-bytes def encrypt(self, plaintext, key): self.splitWord(plaintext) for round in range(1, 33): if (1 <= round <= 8) or (17 <= round <= 24): self.A(round, key) self.printStatus(round) if (9 <= round <= 16) or (25 <= round <= 32): self.B(round, key) self.printStatus(round) return self.appendWords() # ciphertext is a 64-bit integer # key is a list of 10-bytes def decrypt(self, ciphertext, key): self.splitWord(ciphertext) for round in reversed(range(1, 33)): if (25 <= round <= 32) or (9 <= round <= 16): self.Binv(round, key) if (17 <= round <= 24) or (1 <= round <= 8): self.Ainv(round, key) return self.appendWords() def A(self, round, key): c1 = self.w1 c2 = self.w2 c3 = self.w3 self.w1 = self.G(round, key, c1) ^ self.w4 ^ round self.w2 = self.G(round, key, c1) self.w3 = c2 self.w4 = c3 def Ainv(self, round, key): c1 = self.w1 c2 = self.w2 self.w1 = self.Ginv(round, key, c2) self.w2 = self.w3 self.w3 = self.w4 self.w4 = c1 ^ c2 ^ round def B(self, round, key): c1 = self.w1 c2 = self.w2 c3 = self.w3 self.w1 = self.w4 self.w2 = self.G(round, key, c1) self.w3 = c1 ^ c2 ^ round self.w4 = c3 def Binv(self, round, key): c1 = self.w1 self.w1 = self.Ginv(round, key, self.w2) self.w2 = self.Ginv(round, key, self.w2) ^ self.w3 ^ round self.w3 = self.w4 self.w4 = c1 # w is a 16-bit integer def G(self, round, key, w): g = [0] * 6 g[0] = (w >> 8) & 0xff g[1] = w & 0xff j = (4 * (round - 1)) % 10 for i in range(2, 6): # gives i = 2,3,4,5 g[i] = self.F[g[i - 1] ^ key[j]] ^ g[i - 2] j = (j + 1) % 10 return (g[4] << 8) | g[5] # w is a 16-bit integer def Ginv(self, round, key, w): g = [0] * 6 g[4] = (w >> 8) & 0xff g[5] = w & 0xff j = (4 * (round - 1) + 3) % 10 for i in reversed(range(4)): # gives i=3,2,1,0 g[i] = self.F[g[i + 1] ^ key[j]] ^ g[i + 2] j = (j - 1) % 10 return (g[0] << 8) | g[1] # append the four 16-bit words w1,w2,w3,w4 to return a 64-bit word def appendWords(self): x1 = self.w1 << 3 * 16 x2 = self.w2 << 2 * 16 x3 = self.w3 << 1 * 16 x4 = self.w4 return x1 | x2 | x3 | x4 # w is a 64-bit word. This function splits w into # four 16-bit words which are stored in w1, w2, w3, w4 def splitWord(self, w): self.w1 = (w >> (16 * 3)) & 0xffff self.w2 = (w >> (16 * 2)) & 0xffff self.w3 = (w >> (16 * 1)) & 0xffff self.w4 = w & 0xffff # print the round number and the current values of w1,w2,w3,w4 def printStatus(self, round): w = self.appendWords() # print("round=" + str(round) + " " + hex(w)) def defineF(self): self.F = [0xa3, 0xd7, 0x09, 0x83, 0xf8, 0x48, 0xf6, 0xf4, 0xb3, 0x21, 0x15, 0x78, 0x99, 0xb1, 0xaf, 0xf9, 0xe7, 0x2d, 0x4d, 0x8a, 0xce, 0x4c, 0xca, 0x2e, 0x52, 0x95, 0xd9, 0x1e, 0x4e, 0x38, 0x44, 0x28, 0x0a, 0xdf, 0x02, 0xa0, 0x17, 0xf1, 0x60, 0x68, 0x12, 0xb7, 0x7a, 0xc3, 0xc9, 0xfa, 0x3d, 0x53, 0x96, 0x84, 0x6b, 0xba, 0xf2, 0x63, 0x9a, 0x19, 0x7c, 0xae, 0xe5, 0xf5, 0xf7, 0x16, 0x6a, 0xa2, 0x39, 0xb6, 0x7b, 0x0f, 0xc1, 0x93, 0x81, 0x1b, 0xee, 0xb4, 0x1a, 0xea, 0xd0, 0x91, 0x2f, 0xb8, 0x55, 0xb9, 0xda, 0x85, 0x3f, 0x41, 0xbf, 0xe0, 0x5a, 0x58, 0x80, 0x5f, 0x66, 0x0b, 0xd8, 0x90, 0x35, 0xd5, 0xc0, 0xa7, 0x33, 0x06, 0x65, 0x69, 0x45, 0x00, 0x94, 0x56, 0x6d, 0x98, 0x9b, 0x76, 0x97, 0xfc, 0xb2, 0xc2, 0xb0, 0xfe, 0xdb, 0x20, 0xe1, 0xeb, 0xd6, 0xe4, 0xdd, 0x47, 0x4a, 0x1d, 0x42, 0xed, 0x9e, 0x6e, 0x49, 0x3c, 0xcd, 0x43, 0x27, 0xd2, 0x07, 0xd4, 0xde, 0xc7, 0x67, 0x18, 0x89, 0xcb, 0x30, 0x1f, 0x8d, 0xc6, 0x8f, 0xaa, 0xc8, 0x74, 0xdc, 0xc9, 0x5d, 0x5c, 0x31, 0xa4, 0x70, 0x88, 0x61, 0x2c, 0x9f, 0x0d, 0x2b, 0x87, 0x50, 0x82, 0x54, 0x64, 0x26, 0x7d, 0x03, 0x40, 0x34, 0x4b, 0x1c, 0x73, 0xd1, 0xc4, 0xfd, 0x3b, 0xcc, 0xfb, 0x7f, 0xab, 0xe6, 0x3e, 0x5b, 0xa5, 0xad, 0x04, 0x23, 0x9c, 0x14, 0x51, 0x22, 0xf0, 0x29, 0x79, 0x71, 0x7e, 0xff, 0x8c, 0x0e, 0xe2, 0x0c, 0xef, 0xbc, 0x72, 0x75, 0x6f, 0x37, 0xa1, 0xec, 0xd3, 0x8e, 0x62, 0x8b, 0x86, 0x10, 0xe8, 0x08, 0x77, 0x11, 0xbe, 0x92, 0x4f, 0x24, 0xc5, 0x32, 0x36, 0x9d, 0xcf, 0xf3, 0xa6, 0xbb, 0xac, 0x5e, 0x6c, 0xa9, 0x13, 0x57, 0x25, 0xb5, 0xe3, 0xbd, 0xa8, 0x3a, 0x01, 0x05, 0x59, 0x2a, 0x46] def encrypt_string(self, input_string, key): # Check if the input string length is 8 if len(input_string) != 8: print("Input string must be 8 characters long.") return None # Convert the input string into a numerical representation numerical_input = 0 for char in input_string: numerical_input <<= 8 # Shift left by 8 bits numerical_input |= ord(char) # Add ASCII value of the character # Encrypt the numerical input using SkipJack algorithm ciphertext = self.encrypt(numerical_input, key) return ciphertext def xor(a, b): return [x^y for x, y in zip(a, b)] def encrypt_cfb(Kroot: list[int], IV: list[int], Kprev: list[int]): K = [iv for iv in IV] for i in range(0, 32, 4): sj = SkipJack() Kj = int.from_bytes(bytes(K[i:i+4]), 'big') Kj = sj.encrypt(Kj, Kroot) Kj = list(Kj.to_bytes(8, 'big')) Kj = xor(Kj, Kprev[i:i+4]) K.extend(Kj) return K[8:]