HC-9 Cipher Machine Simulator

A simulator of the HC-9, a mechanical cipher machine built by Transvertex in the early '50s. Based on the description from Cryptomuseum Transvertex HC-9

HC-9 is a masterpiece of mechanical engineering and was used for messages that had to remain secret for a few hours. The key space of the HC-9 compares quite favourably with German Enigma (see Cipher Machines Transvertex HC-9 )

A simple encryption/decryption example is provided in the project:

Suppose that we need to transmit the following message:

MEET ME TOMORROW AT MIDNIGHT AT THE USUAL PLACE

Using a randomly picked rotor settings: BLVGM ,we get the message to transmit

FQLMJ CJCCE PVBFC NYGCT BAANK IKXOO TPYCE PZOP

on the other side, when the message is received, with the same rotor settings (BLVGM) we get back the original message

MEETM ETOMO RROWA TMIDN IGHTA TTHEU SUALP LACE

How strong is the encryption of HC-9?

The key space of HC-9 can be calculated for various combinations of rotors and whether all the positions of the rotors can be used as initial state. (see Calculation of the Key Space of the HC-9 in Cipher Machines Transvertex HC-9). As stated in this page, [...] The theoretical key space for the Enigma is 3.28 X 10 ^ 114 but the practical key space was greatly reduced to 1.07 X 10^23 [...]

The original HC-9 for reference

HC-9 Key Space with 5 rotors , using Letters only for initial state
  rotors combinations: 11,881,376
  rotors pins combinations: 2,923,003,274,661,805,836,407,369,665,432,566,039,311,865,085,952
  alphabets combinations: 126,493,657,289,880
 = 4,393,036,292,980,624,879,041,381,919,139,963,735,122,550,448,068,968,993,938,046,986,485,760
 ~ 4.393 x 10^69

Key space: ~ 4.393 x 10^69 . The key space is larger than the practical key space of Enigma.

The original HC-9 if all the positions on the rotors were used as starting point

HC-9 Key Space with 5 rotors , using all positions for initial state 
  rotors combinations: 35,303,730
  rotors pins combinations: 2,923,003,274,661,805,836,407,369,665,432,566,039,311,865,085,952
  alphabets combinations: 126,493,657,289,880
 = 13,053,249,654,550,859,762,451,723,276,849,340,675,234,757,146,815,815,166,556,503,854,284,800
 ~ 1.305 x 10^70

Key space: ~ 1.305 x 10^70

The HC9 with more rotors and using all the positions of the rotors as starting point

This is not practical for the design and size of HC-9 as one of the biggest issues would be that the alphabets' drum would be large and hard to be accomodated by such a small machine. But for the sake of comparison, IF HC-9 had rotors with these pin sizes: [29, 31, 33, 34, 35, 37, 41, 47, 53, 59]

HC-9 Key Space with 7 rotors, using Letters only for initial state

  rotors combinations: 8,031,810,176
  rotors pins combinations: 883,423,532,389,192,164,791,648,750,371,459,257,913,741,948,437,809,479,060,803,100,646,309,888
  alphabets combinations: 505,974,629,157,984
 = 3,590,137,980,724,869,295,443,467,174,738,845,665,334,668,728,251,068,248,370,258,330,046,241,824,933,085,486,071,984,152,379,392
 ~ 3.590 x 10^96

Key space: ~ 3.590 x 10^96

HC-9 Key Space with 7 rotors, using all positions for initial state

  rotors combinations: 53,555,758,410
  rotors pins combinations: 883,423,532,389,192,164,791,648,750,371,459,257,913,741,948,437,809,479,060,803,100,646,309,888
  alphabets combinations: 505,974,629,157,984
 = 23,938,882,784,954,196,689,620,225,634,062,454,378,271,804,192,549,203,111,811,619,507,234,550,871,008,264,315,327,937,742,110,720
 ~ 2.393 x 10^97

Key space: ~ 2.393 x 10^97

HC-9 Key Space with 8 rotors, using all positions for initial state

  rotors combinations: 2,517,120,645,270
  rotors pins combinations: 124,330,809,102,446,660,538,845,562,036,705,210,025,114,037,699,336,929,360,115,994,223,289,874,253,133,343,883,264
  alphabets combinations: 1,011,949,258,311,872
 = 316,695,234,294,301,132,532,726,160,402,984,597,526,383,372,676,155,509,907,711,375,026,531,057,776,126,730,051,013,851,441,059,443,793,297,837,916,160
 ~ 3.166 x 10^113

Key space: ~ 3.166 x 10^113

HC-9 Key Space with 9 rotors, using all positions for initial state

  rotors combinations: 133,407,394,199,310
  rotors pins combinations: 1,119,872,371,088,902,105,278,721,140,284,222,139,060,822,748,617,324,767,449,994,550,481,895,935,590,080,472,690,438,746,635,803,557,888
  alphabets combinations: 2,023,898,516,607,360
 = 302,368,930,299,011,461,928,063,197,625,643,153,015,243,437,999,749,738,874,352,461,094,538,054,925,911,739,488,542,240,354,647,802,094,247,975,051,465,718,497,511,525,580,800
 ~ 3.023 x 10^131 

Key space: ~ 3.023 x 10^131

HC-9 Key Space with 10 rotors, using all positions for initial state

  rotors combinations: 7,871,036,257,759,290
  rotors pins combinations: 645,562,469,521,727,147,413,979,793,000,752,968,582,426,448,207,305,878,207,664,839,135,161,905,504,210,298,657,411,338,320,034,457,858,975,792,993,186,873,344
  alphabets combinations: 4,047,797,033,149,184
 = 20,567,850,881,602,244,475,951,023,959,801,460,394,840,945,394,439,340,295,798,069,676,872,155,800,265,056,569,888,963,752,461,034,955,842,616,942,617,856,217,167,014,924,446,876,414,531,507,941,539,840
 ~ 2.056 x 10^151

Key space: ~ 2.056 x 10^151