There are two main ways to communicate during Operation Tinker Bell. All messages between Langley and its stations abroad are encrypted off-line and then sent by teletype. Most operational communications between the agency and its agents in the field is done by one-way shortwave broadcasts, encrypted with the unbreakable one-time pad system. Some agents, operating in hostile environments, use clandestine shortwave transmitters to send encrypted messages.

All messages relating to Operation Tinker Bell are stored in the Comms Registry Section, and decrypting and analyzing those messages is your main task. Each message is registered under a unique file number, formatted as TB-0000. Make sure to decrypt the oldest messages (lowest file number first).

The TSEC/KL-7 Cipher Machine

All operational messages that are sent by teletype through government communications lines or commercial cable are encrypted off-line with the KL-7 before transmission, to provide the highest level of secrecy. Your task, among others, is to decrypt, analyze, and document the KL-7 traffic.

The KL-7 has been distributed to our services by the National Security Agency. You can download the KL-7 Simulator that works exactly like the real machine. Windows and Java version are available.

Please read the manual carefully to get familiar with the encryption procedures and train your skills on the example messages. You can learn more about this fascinating Cold War machine on the technical details and history page.

Decrypting a Message

The internal key settings of the KL-7 cipher machine are changed daily at midnight, according to the secret key sheet. You must retrieve the proper machine settings for a particular message date from the Crypto Room. Below, the key in its original format (click to enlarge).

To facilitate the reading and setting of keys, we use an easier format in the Crypto Room, which is identical to the KL-7 simulator rotor settings format. These setting are also used in the KL-7 sim training messages, containing actual US Navy messages during the Cuban missile crisis.

DTG 180000Z - 182400Z FEB 64 POSITION 1 2 3 4 5 6 7 8 ROTOR CORE E H F L I A G B ALPHA RING SET 4 28 4 16 9 32 8 11 NOTCH RING 5 10 6 7 1 8 3 NOTCH RING SET C M+ E B E+ Y K 36-45 LETTER CHECK : ASMTH ISXPI BASIC ROTOR ALIGNMENT: XEG BVEQ

Each key setting contains the period in which the key is valid and the eight rotor positions. Below them the selection of the eight rotor cores and their alphabet ring setting. Next, the selection of the notch rings and their setting. Note that the fourth rotor has no notch ring and doesn't move. Underneath the settings are the 36-45 Letter Check (10 letters) to verify the correct key setting and the Basic Rotor Alignment (see KL-7 sim manual).

Make sure to correctly apply the above example key setting example to decipher the following message. Once you finished the settings, always perform the 36-45 Letter Check to verify the key settings (info in sim manual)

The CODRESS Message Format

Each message has a standard format. Message urgency is denoted by a letter:

R = Routine
P = Priority
O = Immediate
Z = Flash

Standard DTG (date time group) for all messages is always Zulu time (a.k.a. UTC). P 180830Z FEB 64 thus indicates a Priority message from February 18, 1964 at 0830 hours Zulu.

The following example shows the format of a complete CODRESS message.

VZCZC NDZ104 UU PP RUFDSC DE RGFBHL 1024 1600832 ZNR UUUUU P 180830Z FEB 64 FM ****** SPECIAL LIAISON SEC BERLIN TO ******* SPECIAL LIAISON WASHINGTON GR 15 BT FOXTROT BRAVO INDIA XRAY NOVEMBER ALFA ECHO QSZUL FYTYY CPKSF ZDVPR RJDAU TDNOH GBOYV DWOJX STGGI JTGPF XLVKD KXHNZ BLKIT KKDVG IOKPW BT NNNN

When the teleprinter message arrives at the COMCEN, the header is torn off and the addressee only receives the part starting from the DTG line, with all routing indicators blackened. For encrypted message, GR (groups count) is added. After the first BT (break) follows the spelled-out KL-7 message indicator and all cipher groups.

The possible teletype security levels are Unclassified (U), Restricted (R), Confidential (C), Secret (S) and Top Secret (T). However, messages containing encrypted groups are always unclassified (U). The actual security level and addressees are included in the ciphertext. If the cipher clerk encounters during deciphering a security level above his clearance, he halts decryption and personnel with the proper clearance will continues the decipherment.

Our services use the encryption procedure with random spelled-out message key (the second example at page 7 of the KL-7 simulator help file). First, make sure you have set the proper internal key settings for that day, as shown in the key sheet example above. Then, for each new message, you must retrieve the secret rotor alignment (steps 1 to 3) and then decrypt the message (step 4). Proceed as follows to decrypt the example message from above:

Set the KL-7 selector (main switch) in ‘P’ and set the Basic Rotor Alignment (XEG BVEQ) for the key example day.
Switch to ‘E’ and type in the spelled-out message indicator (FBIXNAE) from the message.
Switch to ‘P’ and set the output result from step 2 (FSA MQOV) as rotor alignment for the actual message.
Switch to ‘D’ and type in all five-letter groups to decrypt the message, starting from QSZUL...

Carefully follow the steps! Don't switch multiple times between P and E positions during the decryption process, as this will change the rotor positions and render the message illegible!

You can speed up the process with the Auto Typing function. Follow steps 1 through 4 from above but instead of typing in all five-letter groups by hand, you click on the power cable on the right of the KL-7 keyboard. The Auto Typing window will appear.

Copy all five-letter groups from the message, paste them into the Auto Typing text box and click the ‘Start’ button. You can abort with the ‘ESC’ key. When finished, you can click on the paper ribbon at the bottom of the machine to see all output text. More information on keying procedures is found in the KL-7 manual.

Important note! The KL-7 encrypts letters, numbers and spaces into a letters-only ciphertext. Therefore, the SPACE, FIG and LET keys piggyback on the letters X, J and V. To achieve this, before encryption, the letter Z is changed into X, the letter J into Y and the FIG key into J. As a result, during decryption, the original letter Z is decrypted as X and the letter J as Y. Therefore, words like XEBRA (ZEBRA) or YEEP (JEEP) are not decryption errors. When a decrypted word contains the letters X or Y, the intended letter wil be obvious, as it is phonetically similar. Any original plaintext X or Y is unaffected by the piggyback system and remains X or Y after decryption. More info in the KL-7 Letters and Figures section.

Covert Radio Communications

To obtain the highest level of security over radio waves, our clandestine service uses the unbreakable one-time pad system. These so-called numbers messages are sent according to a predetermined and varied time and frequency schedule, unique to each operative, who knows exactly when to listen to a one-way broadcast or to send his own messages. Likewise, the service knows the exact time and frequency to expect radio messages from its operatives in the field.

Each one-time pad set consists of two booklets with identical trule random numbers. One black OUT booklet to encrypt outgoing messages and one red IN booklet for incoming messages. To communicate in both directions, you need two different booklet pairs. The black OUT pads are destroyed immediately after use. The IN pads are red as a warning, because the compromise of that booklet will enable any adversary to decrypt intercepted messages.

The sender converts the plain text into digits with the help of a conversion table and encrypts the digits by subtracting the one-time pad digits (without borrowing) from the message digits. The result is a radio message containing nothing more than the following information:

221 221 221 04598 16633 71492 18478 65037 74850 14004 46968 18082 22082 30128 87558 11445

The first line may contain the (optional) agent ID of the addressee (see Case Files). The first five-digit group (here 04598) is the key indicator, which identifies the one-time pad, used to encrypt the message. The following five-digit groups are the actual encrypted message. The receiver can find the proper one-time pad, required to decrypt that particular message, by checking the key indicator against the first five-digit group of his one-time pads. The operational one-time pads are found in the Crypto Room.

To decrypt the incoming example radio message from above, we use the following example one-time pad.

IN 04598 63693 00154 09795 84943 10971 76289 23007 61500 60504 60093 23542 79355 15363 20459 06628 17065 81290 11161 35668 38841 68860 34485 94774 90642 74814 84649 31408 46490 81382 94731 97027 55341 98510 91799 48757 40672 75953 42371 40114 77961 78020 18769 05716 17947 98342 74811 64779 11242 27692

Write the message groups out on paper, write the one-time pad groups underneath the message and add the digits together, from left to right, and without carry (8 + 4 = 2, not 12!).

Radio Msg: 04598 16633 71492 18478...
OTP:      +04598 63693 00154 09795...
--------------------------------------
Decrypted: KEYID 79226 71546 17163...

Important note: the Key Indicator of both message and one-time pad should be disregarded since these are no part of the actual message.

Finally, the result (stripped from key indicator) is converted back into plain text with the help of the conversion table, shown below. If the digit is 0 through 6, it's a single-digit conversion. If the digit is higher than 6, it's a double-digit conversion. FIG is used before and after digits. Digits are written out three times to exclude errors (e.g. 111777555 is converted back into 175).

79 2  2  6  71 5  4  6  1  71 6 ...
M  E  E  T  C  O  N  T  A  C  T ...

Learn more about one-time pads and numbers stations.

Copyright Notice

The content of the Operation Tinker Bell, including all ciphertext messages and their plaintext versions, are protected by international copyright laws. It is not permitted to publish or distribute the encrypted messages or their plaintext version in digital, printed, or any other form.

STRICKLY KEEP STATE AND MILITARY SECRET!

Cipher Machines and Cryptology