Sunday, May 16, 2010

Other electronic code breaking machines and the Testery and Newmanry results

The other code breaking electronic machines in the Newmanry.

Various cryptographic problems required the building of specialist machines.

There was still the need for multiple paper tape comparison, so Heath Robinson evolved into Old Robinson, the first upgrade, then to Super Robinson. The ultimate multi tape machine was Mrs Miles. It had four tape readers and its name derived from a contemporary lady who had quadruplets.

There was also a proposal for a combined Robinson and Colossus, called Robinson and Cleaver, but it is not clear whether this was ever built.

More important were the Dragon series. These were designed to "drag" a series of characters along a cipher text, (usually a DeChi), looking for significant match points. The ultimate machine of this type was Aquarius. This used voltage storage on a large bank of capacitors to hold patterns of bits for testing matches against cipher or DeChi streams. (The capacitor voltages had to be continuously refreshed, hence Aquarius).

A completely different machine was the 5202 photographic system this did not become operational until 1945. It worked by comparing optically film of cipher text against expected Lorenz patterns. The Newmanry report says that it was successful against a narrow range of problems but was not as flexible as Colossus.

The Testery and Newmanry contribution to the War effort

The contribution to D-Day

Colossus reduced the time to break Lorenz messages from weeks to hours. In January 1944 it was just in time for the deciphering of messages which gave vital information to Eisenhower and Montgomery prior to D-Day, 6th June 1944. These deciphered Lorenz messages showed that Hitler had swallowed the deception campaigns, the phantom army in the South of England, the phantom convoys moving east along the channel; that Hitler was convinced that the attacks were coming across the Pas de Calais and that he was keeping Panzer divisions in Belgium.
After D-Day the French Resistance and the British and American Air Forces bombed and strafed all the telephone and teleprinter land lines in Northern France, forced the Germans to use radio communications and suddenly the volume of intercepted messages went up enormously. Here are some of the German radio links using Lorenz, which were intercepted and broken. They all had FISH names, like JELLYFISH, the German High Command link from Berlin to Western Europe Command.
The Mark 1 had been rapidly augmented by the Mark 2 Colossus in June 1944 and eight more were quickly built to handle the increase in messages. The Mark 1 was upgraded to a Mark 2 and there were thus ten Mark 2 Colossi in the Park by the end of the war. By the end of hostilities, 63 million characters of high grade German messages had been decrypted — an absolutely staggering output from just 550 people at Bletchley Park, plus of course the considerable number of interceptors at Knockholt, with backups at Shaftesbury and Coupar in Scotland.

The Colossus its purpose and operation

Colossus, the revolution in code breaking

Heath Robinson worked well enough to show that Max Newman's concept was correct. Newman then went to Dollis Hill where he was put in touch with Tommy Flowers, the brilliant Post Office electronics engineer. Flowers went on to design and build Colossus to meet Max Newman's requirements for a machine to speed up the breaking of the Lorenz cipher. Tommy Flowers' major contribution was to propose that the wheel patterns be generated electronically in ring circuits thus doing away with one paper tape and completely eliminating the synchronisation problem.
This required a vast number of electronic valves but Tommy Flowers was confident it could be made to work. He had, before the war, designed Post Office repeaters using valves. He knew that valves were reliable provided that they were never switched on and off. Nobody else believed him!

Colossus design started in March 1943. By December 1943 all the various circuits were working and the 1,500 valve Mark 1 Colossus was dismantled, shipped up to Bletchley Park, and assembled in F Block over Christmas 1943. The Mark 1 was operational in January 1944 and successful on its first test against a real enciphered message tape. This is a 1945 photograph of a Mk II Colossus. No pictures of the Mk I have been found, but the Mk I did not have the large switch panel rack with the sloping plug panel on its front and only had a sigle bedstead frame, like Heath Robinson.

The Colossus Computer

Each of the ten Colossi occupied a large room in F Block or H Block in Bletchley Park.
The racks were 90 inches, (2.3m), high of varying widths. There were eight racks arranged in two bays about 16ft (5.5m) long plus the paper tape reader and tape handler (known as the bedstead). The front bay of racks, spaced 5ft (1.6m) from the rear bay, comprised from right to left, the J rack holding the master control panel, the plugboard some cathode followers and the AND gates.
Next came the K rack which contained the very large main switch panel together with the very distinctive sloping panel at the front which was a duplicate patch panel for the thyratron rings. Next came the S rack which held the relays used for buffering counter output and making up the typewriter drive logic. The left hand rack at the front was the C rack which held the counter control logic on the front and the decade counters on the back.

The rear bay of Colossus contained four racks, the R rack holding the staticiser and delta boards for the paper tape reader output and the K and S-wheel thyratron ring outputs, the M rack for the M-wheel staticisers and S-wheel motion logic. The very large W rack held, on one side all the thyratrons making up the wheel rings, 501 in all, and on the other side the 12 thyratron ring control panels. Also on the W rack were the link boards for the wheel patterns and the uniselectors for setting wheel start positions. The end rack of the back bay held the power packs. These were 50 volt Westat units stacked up in series to give +200 volts to -150 volts. The total power consumption was about 5 Kilowatts most of which was to the heaters of the valves.

The circuit layout was all surface mounting on metal plates bolted to the racks. The valve holders were surface mounting with tag strips for the components. This form of construction had much to commend it, firstly both sides of a rack could be used, secondly wiring and maintenance were very easy and lastly cooling of the valves was expedited by them being horizontal.

How Colossus worked

Colossus read teleprinter characters, in the international Baudot code, at 5,000 characters per second from a paper tape. These characters were usually the intercepted cipher text which had been transmitted by radio. The paper tape was joined into a loop with special punched holes at the beginning and end of the text. The broad principle of Colossus was to count throughout the length of the text the number of times that some complicated Boolean function between the text and the generated wheel patterns had either a true or false result. At the end of text the count left on the counter circuits was dumped onto relays before being printed on the typewriter during the next read through the text, an early form of double buffering.

Colossus had two cycles of operation. The first one was controlled by the optical reading of the sprocket holes punched between tracks 2 and 3 on the paper tape. The sprocket signal was standardised to 40 microseconds wide. The optical data from the paper tape was sampled on the back edge of the standardised sprocket pulse as was the outputs from the rings of thyratrons representing the Lorenz wheel patterns. The result of the logical calculation was sampled on the leading edge for feeding into the counter circuits.

The second cycle of operations occurred at the beginning and end of the text punched onto the paper tape. The paper tape was joined into a loop and special holes were punched just before the start of text between channels three and four (called the start ) and just after the end of text between channels four and five (called the stop). This long cycle of operations began with the electrical signal from the photocell reading the stop hole on the tape. This stop pulse set a bistable circuit which stayed set until the optical signal from the start hole was read. The setting of this bistable thus lasted for the duration of the blank tape where the text was joined into a loop, typically about 100 millisec.

The first operation after the stop pulse was to release any settings on the relays from the previous count. Next the new count was read onto the relays. Then the counters and the thyratron rings were cleared and then the thyratron rings were struck at the next start point to be tried. When the bistable was reset by the start pulse, sprocket pulses were released to precess the thyratron rings, to sample the data read from the paper tape and to sample the calculation output to go to the counters.

The various components of Colossus were the optical reader system, the master control panel, the thyratron rings and their driver circuits, the optical data staticisors and delta calculators, the shift registers, the logic gates, the counters and their control circuits, the span counters, the relay buffer store and printer logic.

The optical reader system

In order to break the Lorenz codes in a reasonable time the cipher text had to be repeatedly scanned at very high speed. This meant at least 5,000 characters per second and in the 1942 this implied hard vacuum photocells to optically read the holes in the paper tape. The smallest photocells available were some developed for proximity fuses in anti aircraft shells. Six of these in a row meant an optical projection system to enlarge the image of the paper tape about 10 times. Dr Arnold Lynch designed the paper tape reader and used slits cut into black card to form a mask in front of the photocells. The output from the data channels went to the staticiser and delta circuits.

The master control panel

This was where the start and stop pulses from the optical reader set and reset the bistable. Monostable delay circuits generated the voltage waveforms for releasing the relays, for staticising the counters, for resetting the counters and thyratron rings, and for striking the rings. Gate circuits controlled the flow of sprocket pulses.

The thyratron rings and their driver circuits

These circuits were the most complex on Colossus.
Thyratrons are gas-filled triodes which strike a discharge arc between anode and cathode when the grid voltage is raised to allow electrons to flow. This discharge when struck continues quite independent of the grid voltage. Thus the thyratron acts as a one-bit store. It can only be switched off by driving both the anode and the grid negative with respect to the cathode.
To construct a shift register with thyratrons requires that the striking of the next thyratron in the ring also quenches the previous thyratron. This leads to a biphase circuit with anodes of alternate thyratrons connected together and the grid voltage partially biased by the cathode voltage of the previous thyratron. The complication arises when a Lorenz wheel contains an odd number of setting lugs. The thyratron ring controller for this requires a complete set of circuits to handle just the odd thyratron in order to get back to the biphase circuits for the rest of the ring.

The thyratrons in a ring conduct sequentially stepped round by the sprocket pulses. Each thyratron cathode is brought out to a patch panel which allows the cathode pulse to be connected to a common output line when a link is plugged into the patchboard. Thus as the ring precesses round a sequence of pulses appears on the common output line. By selecting the link positions this sequence can replicate the mechanical lugs set on the Lorenz wheel. Alongside the patch panel is a Uniselector which selects the thyratron cathode to which the ring strike pulse goes. This is the start position of the ring when sprocket pulses come in at the start of text. The common line output went to the staticiser and delta circuits.

The staticisors and delta circuits

These circuits take the raw signals from the paper tape reader and the thyratron rings, sample them on the back edge of the clock pulse and set them to standard voltages of ± 80 v. Also on these boards are circuits giving a delay of one clock pulse. This is achieved with integrator capacitors which "hold" the previous data signal for long enough for it to be sampled on the next sprocket pulse. This delayed signal is available as an output but also on the board is an adder circuit which produces the delta signal, i.e. a 'one' when current data is different from previous, and a 'zero' when current equals previous.

The shift registers

These are the same circuits used as used on the delta boards, just integrators sampled on the next sprocket pulse.
Up to 5 shift elements could be connected in cascade giving a 5 bit shift register. This is thought to be the first recorded design or use of a shift register. Some of the computational algorithms used this window on previous data to improve the cross-correlation measurement.

The logic gates

Colossus was provided with AND, OR and XOR gates which could be plugged together in any combination.

The counter and counter control circuits

The decade counter circuits were based on a pre-war design by Wynn- Williams. They used a divide by two circuit followed by a ring of five pentodes. Four decades were required for each of the five counters used and each control circuit covered four decades of counters. The inputs to the control circuits were the output from the logic gates, the sprocket pulse for strobing and the reset pulse from the master control panel. Also on the control panels were comparator circuits between the outputs of the decade counters and switches on another panel. These switches could be set to any number in the range 0 to 9999. The output of the comparator could be included in the logic calculations thus for instance suppressing printing of scores below a set value.

The span counters

These were the same design of counters and counter control circuits with switches on another panel which could be set in the range 0 to 9999. The purpose of the span counters was to be able to ignore sections of the cipher text which were corrupted, possibly due to fading radio signals. The comparator output was used to gate the sprocket pulses which went to the main counter controllers, cutting off these pulses stopped the sampling of the logic calculation and thus ignored the section of text covered by the span counters.

The relay buffer store and printer logic.

Latching relays held the ending count on the decade counters. The start positions of the thyratron rings and the count for the previous run through the text are clocked out sequentially on to the typewriter by the printer relay and uniselector logic.

Programming Colossus

Programming of the cross-correlation algorithm was achieved by a combination of telephone jack-plugs, cords and switches. The main plug panel was on the rack nearest to the paper tape reader. The direct and delta signals from the paper tape reader and the K-wheel thyratron rings were on this panel. The changeover from direct to delta could also be achieved by switches. Also on the main plug panel were the input and output sockets for the AND gates and the so called "Q" sockets which took the calculated output to the main switch panel on the next rack to the left. This very large switch panel allowed signals to be combined through further logic gates and the results switched to any of the five result counters. As an example take the simple double-delta algorithm as devised by Bill Tutte. This requires two wheels to be run simultaneously: so take K4 and K5. First the delta outputs from channel 5 of the paper tape reader is combined in an XOR gate with the delta output of the K5 thyratron ring. Then this result is XORed with the XOR output of delta channel 4 and the delta output of the K4 thyratron ring. This result is plugged to Q1 and on the switch panel Q1 is switched to counter 1. The output can be negated before being counted so that the count can represent either the number of times the double-delta calculation equals one, or the number of times it equals zero.

The end of Colossus

After VJ Day, suddenly it was all over. Eight of the ten Colossi were dismantled in Bletchley Park. Two went to Eastcote in North London and then to GCHQ at Cheltenham. These last two were dismantled in the 1960s and in 1960 all the wartime drawings of Colossus were burnt. Of course its very existence was kept secret.

Saturday, May 15, 2010

The machine age comes to Fish code breaking

The machine age comes to Fish code breaking

The mathematician Max Newman now came on the scene. He thought that it would be possible to automate some parts of the process for finding the settings used for each message. He approached TRE at Malvern to design an electronic machine to implement the double-delta method of finding wheel start positions which Bill Tutte had devised. The machine was built at Dollis Hill and was known as Heath Robinson after the cartoonist designer of fantastic machines.
Max Newman

    The Wynn-Williams proposal.

The Logic Circuits

When Wynn-Williams was asked to produce electronic circuits to implement the double delta algorithm he chose to use a phase modulated carrier from a master oscillator at 25kc/s to perform the XOR logic.

He decided to use 0 and 180 degrees of phase to represent 0 and 1. The elegance of this is that if a "1" causes 180 degrees phase shift, then another 1 returns the phase to zero and thus this implements an XOR function (0 + 0 = 0, 1 + 1 = 0, 0 + 1 = 1, 1 + 0 = 1).

The 180 degrees phase shift was achieved via a diode bridge circuit and a balanced transformer. The biasing of the bridge, + - 10 volts, determined whether the input carrier went straight through (no phase change) of shifted 180 degrees. A triode valve amplifier was included with each bridge circuit to compensate for the losses in the bridge and to give unity gain from input to output.
The output phase at the end of a series of logic circuits was compared with the phase input to the logic circuits in a detector circuit. This gave a voltage output of nearly zero if the input and output are in anti phase or some, much larger, positive voltage if they were in phase. The output voltage from the detector was sampled by a pulse derived from the sprocket hole signal from the tape reader. The result of this sampling, either a pulse if the detector output was positive, or no pulse if the output was zero was then passed to the decade counters to accumulate a count down the whole length of the tapes.

The Decade Counters

There were four decimal decade counters in series giving a 9999 maximum count. The first stage of the decade counters consisted of a ring of ten thyratrons (gas filled thermionic triode valves). The circuit for this was designed by Wynn-Williams before the war for counting in nuclear particle experiments. A thyratron valve will strike and hold an internal arc discharge when there is a positive voltage on its anode and the grid voltage is raised towards the cathode voltage allowing current to start flowing. Once the discharge is started the grid voltage has no further influence over the anode current. Thus the thyratron "remembers" it has been struck and thus acts as a one bit store. Unfortunately the only way to stop the discharge in a thyratron is to drive the anode negative with respect to its cathode. In the decade thyratron ring the thyratron which had been struck had to prepare the next thyratron in the ring to be struck on the next input pulse, but at the same time the next thyratron struck had to cause the pervious thyratron to be extinguished. In the Wynn-Williams circuit this was achieved by coupling successive thyratron's cathodes together with a large capacitor. The thyratron ring was the fast, least significant, decimal counter. The next two counters, the tens and hundreds, used high speed relays with slow speed relays in the thousands counter. The count was displayed on a lamp panel. There were four sets of counters, each of 9999 capacity. The output from the logic circuits was switched alternately into one of two counter sets, the changeover occurring at the end of reading the data on the two tapes. Each tape were joined end to end in a continuous loop. Special holes were punched into the tapes to signify end of data and start of data. The remaining two counters sets were used to count sprocket holes. These counts allowed the calculation of Chi wheel positions for a particular score. Initially all counts had to be read off the lamp panel and written down, a great source of error. Later a special printer known as a "Gifford" printer was added. This was not a great success.

Heath Robinson

Heath Robinson consisted of three parts, the frame on which the teleprinter paper tapes were mounted and read optically, known as the Bedstead, a wide short rack containing the counters, a lamp output panel and later the Gifford printer on a front table, and a tall 19 inch rack known as the valve rack which contained the logic circuits and a jack field panel for plugging up the algorithms. The short counters rack was produced at TRE and the Bedstead and valve rack at the GPO research labs at Dollis Hill to Wynn-Williams circuit designs. The cover name for the project was "Apparatus Telegraph Transmitting", case number 11951. The Bedstead was designed by Arnold Lynch and Eric Speight. Harry Fensom and Alan Bruce worked on commissioning the system at Dollis Hill. There were difficulties in getting the ring modulator logic to work due to extra phase shifts in the circuits when more than six circuits were connected together one after the other. Allen Coombs relates this problem and tells how he went to Tommy Flowers for advice. Tommy Flowers said "change the frequency" which Allen Coombs did. It solved the problem but neither he nor Tommy Flowers knew why.
Eventually it all worked together and Heath Robinson was moved to Bletchley Park.

Heath Robinson was delivered to Bletchley Park in June 1943 and was first installed in Hut 11 which had been the original Bombe room for Turing Bombes, the machines used to break Enigma.

Harry Fensom and Alan Bruce were the two GPO maintenance engineers assigned to Heath Robinson. Two WRNS(Womens Royal Naval Service) ladies at a time were the operators and Jack Good and Donald Michie were the code breakers.

The first problem was teleprinter tape preparation. At least 2000 characters of cipher text was required, joined end to end to make a continuous loop. Then a similar length of Chi wheel patterns had to be punched up and arranged to be just one character longer than the cipher tape. This was to automatically change the relative wheel patterns by one position after each complete run through the tapes.

Then it was found that the optical readers in the Bedstead gave errors if a long stretch of adjacent holes or no holes occurred on the tapes. This meant adjustments to both texts to compensate for this.

A major problem was keeping the two tapes in synchronism at over 1000 characters per second. Originally the sprocket drive cogs were motorised but this proved impossible to sustain without tearing the tapes and a friction drive was used from the paper tape pulleys with the sprocket shaft just idling to keep synchronisation. This proved to be better but there was still a problem with tape stretching in the distance between the sprocket cogs and the optical reader aperture.

Heath Robinson worked well enough to show that Max Newman's concept was correct. Newman then went to Dollis Hill where he was put in touch with Tommy Flowers, the brilliant Post Office electronics engineer. Flowers went on to design and build Colossus to meet Max Newman's requirements for a machine to speed up the breaking of the Lorenz cipher.

Friday, May 14, 2010

The Lorenz Cipher and how Bletchley Park broke it

The German Lorenz cipher system

The German Army High Command asked the Lorenz company to produce for them a high security teleprinter cipher machine to enable them to communicate by radio in complete secrecy. The Lorenz company designed a cipher machine based on the additive method for enciphering teleprinter messages invented in 1918 by Gilbert Vernam in America. Teleprinters are not based on the 26-letter alphabet and Morse code on which the Enigma depended. Teleprinters use the 32-symbol Baudot code. Note that the Baudot code output consists of five channels each of which is a stream of bits which can be represented as no-hole or hole, 0 or 1, dot or cross.

The Baudot Code

The Vernam system enciphered the message text by adding to it, character by character, a set of obscuring characters thus producing the enciphered characters which were transmitted to the intended recipient. The simplicity of Vernam's system lay in the fact that the obscuring characters were added in a rather special way (known as modulo-2 addition). Then exactly the same obscuring characters, added also by modulo-2 addition to the received enciphered characters, would cancel out the obscuring characters and leave the original message characters which could then be printed. The working of modulo-2 addition is exactly the same as the XOR operation in logic. If A is the plain-text character, and C the obscuring character, then in the table below, F is the cipher-text character. You can also see from this table that the addition of C to F brings you back to A again:
A + C = F      F + C = A
x + . = x      x + . = x
x + x = .      . + x = x
. + x = x      x + x = .
. + x = x      x + x = .
. + . = .      . + . = .
Vernam proposed that the obscuring characters should be completely random and pre-punched on to paper tape to be consumed character by character in synchrony with the input message characters. Such a cipher system (a 'one-time pad system') using purely random obscuring characters is unbreakable.
The difficulty was how to ensure, in a hot war situation, that the same random character tapes were available at each end of a communications link and that they were both set to the same start position. The Lorenz company decided that it would be operationally easier to construct a machine to generate the obscuring character sequence. Because it was a machine it could not generate a completely random sequence of characters. It generated what is known as a pseudo-randomsequence. Unfortunately for the German Army it was more "pseudo" than random and that was how it was broken.

The amazing thing about Lorenz is that the code breakers in Bletchley Park never saw an actual Lorenz machine until right at the end of the war but they had been breaking the Lorenz cipher for two and a half years.

The first intercepts

The teleprinter signals being transmitted by the Germans, and enciphered using Lorenz, were first heard in early 1940 by a group of policemen on the South Coast who were listening out for possible German spy transmissions from inside the UK. Brigadier John Tiltman, one of the top code breakers in Bletchley Park, took a particular interest in these enciphered teleprinter messages. They were given the code name "Fish". The messages which (as was later found out) were enciphered using the Lorenz machine, were known as "Tunny". Tiltman knew of the Vernam system and soon identified these messages as being enciphered in the Vernam manner. Because the Vernam system depended on addition of characters, Tiltman reasoned that if the operators made a mistake and used the same Lorenz machine starts for two messages (a depth), then by adding the two cipher texts together character by character, the obscuring character sequence would disappear. He would then be left with a sequence of characters each of which represented the addition of the two characters in the original German message texts. For two completely different messages it is virtually impossible to assign the correct characters to each message. Just small sections at the start could be derived but not complete messages.

The German mistake

As the number of intercepts, now being made at Knockholt in Kent, increased a section was formed in Bletchley Park headed by Major Ralph Tester and known as the Testery. A number of Depths were intercepted but not much headway had been made into breaking the cipher until the Germans made one horrendous mistake. It was on 30 August 1941. A German operator had a long message of nearly 4,000 characters to be sent from one part of the German Army High command to another — probably Athens to Vienna. He correctly set up his Lorenz machine and then sent a twelve letter indicator, using the German names, to the operator at the receiving end. This operator then set his Lorenz machine and asked the operator at the sending end to start sending his message. After nearly 4,000 characters had been keyed in at the sending end, by hand, the operator at the receiving end sent back by radio the equivalent, in German, of "didn't get that — send it again".
They now both put their Lorenz machines back to the same start position. Absolutely forbidden, but they did it. The operator at the sending end then began to key in the message again, by hand. If he had been an automaton and used exactly the same key strokes as the first time then all the interceptors would have got would have been two identical copies of the cipher text. Input the same — machines generating the same obscuring characters — same cipher text. But being only human and being thoroughly disgusted at having to key it all again, the sending operator began to make differences in the second message compared to the first.
The message began with that well known German phrase SPRUCHNUMMER — "message number" in English. The first time the operator keyed in S P R U C H N U M M E R. The second time he keyed in S P R U C H N R and then the rest of the message text. Now NR means the same as NUMMER, so what difference did that make? It meant that immediately following the N the two texts were different. But the machines were generating the same obscuring sequence, therefore the cipher texts were different from that point on. The interceptors at Knockholt realised the possible importance of these two messages because the twelve letter indicators were the same. They were sent post-haste to John Tiltman at Bletchley Park. Tiltman applied the same additive technique to this pair as he had to previous Depths. But this time he was able to get much further with working out the actual message texts because when he tried SPRUCHNUMMER at the start he immediately spotted that the second message was nearly identical to the first. Thus the combined errors of having the machines back to the same start position and the text being re-keyed with just slight differences enabled Tiltman to recover completely both texts. The second one was about 500 characters shorter than the first where the German operator had been saving his fingers. This fact also allowed Tiltman to assign the correct message to its original cipher text. Now Tiltman could add together, character by character, the corresponding cipher and message texts revealing for the first time a long stretch of the obscuring character sequence being generated by this German cipher machine. He did not know how the machine did it, but he knew that this was what it was generating!

The dénouement

John Tiltman then gave this long stretch of obscuring characters to a young chemistry graduate, Bill Tutte, who had recently come to Bletchley Park from Cambridge. Bill Tutte started to write out the bit patterns from each of the five channels in the teleprinter form of the string of obscuring characters at various repetition periods. Remember this was BC, "Before Computers", so he had to write out vast sequences by hand.

When he wrote out the bit patterns from channel one on a repetition of 41, various patterns began to emerge which were more than random. This showed that a repetition period of 41 had some significance in the way the cipher was generated. Then over the next two months Tutte and other members of the Research section worked out the complete logical structure of the cipher machine which we now know as Lorenz:

This was a fantastic tour de force and at the beginning of 1942 the Post Office Research Labs at Dollis Hill were asked to produce an implementation of the logic worked out by Bill Tutte & Co. Frank Morrell produced a rack of uniselectors and relays which emulated the logic. It was called "Tunny". So now when the manual code breakers in the Testery had laboriously worked out the settings used for a particular message, these settings could be plugged up on Tunny and the cipher text read in.

If the code breakers had got it right, out came German. But it was taking four to six weeks to work out the settings. This meant that although they had proved that technically they could break Tunny, by the time the messages were decoded the information in them was too stale to be operationally useful.

Thursday, May 13, 2010

The Enigma Machine

The Enigma Machine

Invented by Arthur Scherbius in 1918 the Enigma machine is a very ingenious way of achieving seven alphabet substitutions between a text input letter and a ciphered output letter. The alphabetic substitutions are implemented via wiring inside rotors.

Enigma rotors (or wheels)

Before seeing how the Enigma machine was constructed you should see the rotors or wheels which embodied the alphabetic substitutions.

Figure 4: details of an Enigma rotor:
(1) The finger notches used to turn the rotors to a start position.
(2) The alphabet RING or tyre round the circumference of the rotor (see below for an explanation of its significance).
(3) The shaft upon which the rotors turn.
(4) The catch which locks the alphabet ring to the core (5).
(5) The CORE containing the cross-wiring between contacts (6) and discs (7). It is the core which effects the essential alphabetic substitution.
(6) The spring loaded contacts to make contact with the next rotor.
(7) The discs embedded into the core to make contact with the spring-loaded contacts in the next rotor.
(8) The CARRY notch attached to the alphabet ring (see below for explanation).

These rotors were manufactured with their wirings buried inside and they could not be modified in use.
In the 1930s, the Enigma had only three different kinds of rotor, I II and III. These rotors could be assembled on the shaft in any order giving 6 (i.e. 3x2x1) possible configurations.
In 1938 the Germans added rotors IV and V to the repertoire, thus giving 60 (i.e. 5x4x3) configurations by choosing a set of three rotors from the five. Some further wheels were brought into use during the course of the war but basically the rotors remained unchanged throughout.

The Military Enigma Machines

We are now ready to see the machine actually used by the German armed forces, and to go on to the further complications introduced through the ring-setting and the plugboard or Steckerverbindung.

You can readily see three rotors in place. In operation, a current flowed from right to left then back left to right, so the reflector is at the left and the entry disc is at the right.
The entry disc is a fixed disc of 26 contacts. The keyboard contacts are connected to the right hand side. The left hand side of the entry disc has metal contact discs just like the wheel discs. A curious aspect of the Enigma design was that the keyboard was connected to the entry disc in the simple order ABCDEF... and did not take advantage of the opportunity for introducing a further scrambling.
As explained above, it is important that the rotors are interchangeable. Mechanically, this is effected as follows. When the release lever is pulled forward, the reflector slides to the left and the group of three rotors can be taken out on their shaft. Then the operator can assemble a new sequence of rotors on the shaft, and put this back into the machine.
The lamp panel shows the enciphered output letter for the keyboard key pressed. This was rather a primitive aspect of the Enigma as it relied on the operator to observe and write down the lit-up letter at each stage of encipherment and decipherment.

The plugboard

The plugboard or 'Stecker', visible on the front of the machine, was the most important addition made to the basic Enigma when turning it into a machine for military use. The operator simply inserted plugs so as to connect pairs of letters (generally 10 pairs, in wartime use) and this had the effect of hard-wiring such a swapping.Because the plugboard affected both the incoming current from the keyboard and the outgoing current to the lamps. it left unchanged the reciprocal property of the Enigma. It also meant that the military Enigma still had the property that no letter could ever be enciphered to itself. This was a very grave mistake in the design.
To see how this worked in more detail, it is best to forget the physical picture of the Enigma and concentrate on a logical diagram of how the electrical current effected substitutions:

Circuit Diagram of the Enigma with Plugboard

The keyboard was laid out as follows:

The same arrangement was used for the lamp panel and the plugboard.

In this illustration, when key W is pressed on the keyboard (5) current from the battery (4) flows to the plugboard panel socket W, but socket W has been plugged to socket X so current flows up to the entry disc (E) at point X.
The current then flows through the internal wiring in the rotors (2) to the reflector (1). Here it is turned round and flows back through the rotors in the reverse direction emerging from the entry disc at terminal H. Terminal H on the Entry disc is connected to socket H on the plugboard (6) but this socket is plugged to socket I so finally the current flows to lamp I which lights up.
Thus in this instance, the letter W is enciphered to I.

You can now also see that if the key I had been pressed, the lamp W would have lit up. This is because the path from W to I through the steckers and rotors remains the same, though with the current flowing in the opposite direction.
When the W key is pressed the connection to the W lamp is broken and the I lamp lights. If the I key is now pressed down the connection to the I lamp is broken and the W lamp lights.

The motion of the rotors

Now you will recall from our introduction that the whole point of the rotors is that they must rotate, so that every time a letter is enciphered, the machine is in a different configuration. So, when a key on the keyboard is pressed down, a mechanical linkage causes the right hand rotor to turn by 1/26 of a revolution, i.e. by one letter on the alphabet ring.This means that the next time a key is pressed, the substitution effected by the rotors is quite different.
At certain points on the rotation of the right hand rotor, the motion is 'carried' to the middle rotor, M which then moves on one letter. Carry will also occur from the middle to the left hand rotor when the carry notch engages, but obviously this will happen much less often.

The Enigma sent the current through the wires AFTER the mechanical linkage had moved the right-hand wheel and any other wheels knocked on by the carry mechanism. The principle is just the same as the 'carry' on an adding machine knocking on to tens, hundreds and thousands, but there is a subtlety in the design affecting the point at which the knocking-on occurred.
To appreciate this we must first describe the alphabet RING settings.

The ring setting

Referring again to figure 4, not that on each rotor there is a spring loaded catch (4). When this is pulled to the right the ring (or tyre) can be turned with respect to the core of the rotor. In fact the ring for each rotor can be set by the operator in any one of 26 possible settings.The effect of this is that the core which contains the wiring, is turned in relation to the letter showing in the window of the Enigma machine.
At first sight this extra complication might seem rather pointless because it did not change anything to do with the essential scrambling going on inside the system. However the indicator systems, to which we will come later, depended on describing the 'window position' of the rotor, and the ring-setting determined the relationship between the window letters and the actual scramblings. Furthermore, the carry mechanism is affected by the ring setting. The 'carry' point is in fact determined by the position of the carry notch (8) in figure 4, and the crucial point is that this notch is attached to the alphabet RING, and not to the core of the rotor.
The carry notch was arranged to be in a different position for each of the rotors I, II, III, IV, V. This turned out to be a bad cryptographic mistake; it helped first the Poles and then the British analysts at Bletchley Park to identify the right hand rotor in use.

Wednesday, May 12, 2010

How to Thread a Sewing Machine

Threading a sewing machine can be difficult at first. Once you learn how, though, the whole process will take you only a few seconds and you'll be on your way sewing together anything you need. It does require somewhat of a good eye sight and good aim, so get your glasses if you need them to see up close.


  1. Step1
    Raise the needle to its highest position by turning the handwheel toward you.
  2. Step2
    Raise the presser foot. This will allow the thread to easily pass through the threading points and will prevent the machine needle from becoming unthreaded when you begin to stitch.
  3. Step3
    Place a spool of thread on the spool pin located at the top of your sewing machine. If the spool pin runs horizontally, secure the spool of thread with the cap provided.
  4. Step4
    Take hold of the thread end and pass it through the designated threading points on the top of the machine casing, then down toward the tension assembly. The tension assembly is located on the left side of the machine and controls the flow of thread.
  5. Step5
    Take the thread under the tension assembly and back up through the next threading point at the top left of the machine. Make sure the thread has passed between two tension discs as well as the hook that may be attached to the left side of the tension dial.
  6. Step6
    Push the thread end through the lever at the top left of the machine, if applicable, and down through the threading points at bottom left and above the needle.
  7. Step7
    Thread the needle from the front or back of the needle. The threading direction will depend on your machine type.
  8. Step8
    Pull a few inches of thread through the eye of the needle and pull the thread to your left.
  9. Step9
    Insert a wound bobbin into the machine, if necessary, and close the throat plate. A few inches of bobbin thread should be pulled out to the right and sticking out from under the closed throat plate.
  10. Step10
    Take hold of the thread that has been threaded through the machine needle.
  11. Step11
    Rotate the hand wheel toward you until the needle disappears into the bobbin case.
  12. Step12
    Keep holding on to the thread and move the hand wheel so the needle is once again at its highest position. As the needle rises, a loop of bobbin thread will come up as well.
  13. Step13
    Pull the thread out toward your left to draw the bobbin thread loop further out of the bobbin case.
  14. Step14
    Let the top thread go and pull the bobbin thread up until the end comes up. Pull the top and bottom threads under the presser foot and to the back and right of the machine.

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