When Opposite Sides Share the same Crypto

I imagine that very few people think about the cryptographic consequences of a country breaking up but they can be significant, especially if the break-up is violent. The outbreak of the Spanish Civil War, for example, produced within days two opposing armed forces which used the same encryption systems which had to be modified on the fly by people with little cryptographic experience. The same thing happened in France in 1940 when the Free French military broke away from those who accepted the Armistice. One such break-up during the Second World War, that of the division of Italy into areas controlled by Mussolini’s Italian Social Republic based in Salò and those controlled by the Kingdom of Italy and based in Salerno, were written up after the war by Fred Catty, Head of the Italian Diplomatic Section in Berkeley St. (Commercial and Diplomatic Sigint were hived off from Bletchley Park to London early in 1942.)

Italian Diplomatic ciphers had been read without difficulty by GC&CS until in 1941 the Germans committed to joint operations with the Italians in North Africa. The Germans had been reading Italian systems themselves and simply refused to share classified material with their ally. However, the Germans decided that ensuring that the Italians gave nothing away of German intentions was more important than reading their traffic. They informed the Italians about the weakness of their systems and in July 1942 the old systems were gradually replaced by new ones. Fortunately for Berkeley Street the Germans did not bother to supervise Italian use of the new systems so they were never as secure as they should have been. In fact, by the end of 1942 the Italian Diplomatic Section was as successful as it had been before the new systems were introduced. In January 1943 the Italians appear to have had some misgivings and they added an extra level of security which should have brought GC&CS to a full-stop: but operator error neutralised the precautions the Italians had taken.  

In July 1943 Mussolini was deposed but escaped from captivity and set up his own Neo-Fascist Government in North Italy. In September the Royal Italian Government accepted unconditional surrender. Mussolini had his own Foreign Ministry located at Salò (Lake Garda) with its own WT Station while the Royal Italian Foreign Ministry was based at Salerno.

What follows is Mr Catty’s description (from HW 43/4 which hasn’t been released but which is quoted in HW 43/75-77, de Grey’s draft history, which has) of what happened next. It is worth highlighting that that the UK and US were as lax as the Germans had been in supervising their new allies’ security, and that the organisational and geographical separation of communications intelligence and communications security in the UK wasted cryptanalytic effort at Berkeley St.

‘There was quite an extensive array of posts which would claim to represent this Neo-Fascist Government abroad. In all of Europe occupied by the Germans the former Italian Ministers perforce remained Fascist; in addition, in Madrid, besides the 'Royal" Italian Embassy, Mussolini 'accredited' a Dr. Morreale (believed to have been the brother of Clara Petacci) as his 'Ambassador'. In Tokyo the Ambassador preferred interment as a 'Royalist', but Col. Principini, Military Attaché, took over. All these and isolated posts in various countries would now be trying to report to and take orders from Mussolini.

In the South there was now a 'Royal Italian' Government (at Salerno until Rome was taken nearly a year later). The Italian Diplomatic Service was always royalist by tradition. And now all the major ambassadors and ministers in countries where they could safely do so, declared for the King and put themselves at the disposal of the Allies. In Madrid the Royal Embassy handed over all its cyphering material for inspection to the Allied Representatives.

Meanwhile the Salerno Government, being subject to the control of Allied Force Headquarters for its communications, made a case first that it needed to communicate with Royal Italian posts abroad and subsequently that it should have cyphers (deposited if need be) in which to do so.

All the cyphers hitherto used by the Foreign Ministry in Rome had obviously to be considered as now equally useless to either side. The Germans in Rome had ample opportunity of ransacking the "Ufficio Cifra". We know that they did so. At the same time they must have known that Royal Embassies would deliver up their stock to us and that men who knew all this material were in Allied hands. It was a reasonable conclusion that neither we nor the Germans would ever be concerned with these codes and tables again.

It should be recorded that it was the unreasonable that happened. When cypher traffic was intercepted, as in the French case, both sides were found using the compromised cyphers.

Owing to the urgent needs of Japanese and other sections at Berkeley Street the Italian Section had, as soon as Italy surrendered, been quickly dissolved. Fortunately there remained a small nucleus to examine any cypher traffic which might need investigating, and its problem, for the first six months was (again contrary to all reason) not a Fascist, but a Royal, pro-allied cypher.

For the first seven months the Fascist traffic which was intercepted was almost entirely in plain text. This was probably an order made by the Germans, since, from an intercept in December we knew that they were reducing the strength and status of Fascist posts everywhere and they may well at this juncture not have had time to bother with supervising Fascist cyphers.

Traffic was intercepted between Salò and Berlin, Madrid, Tokyo and Budapest. Between September 1943 and January 1944 there were 800 intercepts, none of them separately important, but together giving a picture of the set-up at Salò the attitude of the Germans, and who were Mussolini's adherents abroad.

But there began to be intercepted in January cypher traffic between the Royal Embassy in Madrid and the Salerno Foreign Office which was entirely different from any known Italian Diplomatic Cypher. It was found to be a transposition, believed double since prolonged efforts failed to break it. We were in fact spending our efforts on a system which Allied Military headquarters had approved (and as we later learned) improved for the Italians on our side.

Eventually the key-book was sent to us. The keys at that time were derived from an English illustrated magazine. Though it was a 'deposited' system, it was not certain that the traffic was being read at Caserta [ie Allied Military HQ], and this was therefore done and the contents, when of interest, translated at Berkeley Street.

From this it became clear firstly that the system, being laborious, was unsuited to the long dispatches which diplomats have to send; secondly that the Italians were ignoring rules which were part of the security of the system, and thirdly that Madrid was being told to retransmit messages received in this system to a post which did not hold it. This last would be a major blunder, of which the Italians were quite capable.

But our interception of Royal Italian showed even worse to be going on, of which Allied Force Headquarters in Italy could not be aware, since they controlled only the use of cypher into and out of Italy. Between Madrid and seven other posts various of the old and completely compromised cyphers were being used.

This gradually led the Foreign Office to the conclusion that to advise the Italian Foreign Office and ensure that it used only secure cyphers and used them correctly a joint Anglo-American Mission staffed by Berkeley Street and ASA, Washington should be attached to the Allied Control Commission in Italy. This mission arrived in Rome on 1st October 1944. It consisted of the head of the Italian Section at Berkeley Street with one secretary and of an officer who had worked in the Italian Section at ASA, Washington. It worked in Rome as a subsection of the Communications Section of the Allied Control Commission until the end of hostilities in Italy in May 1945. Its terms of reference were:

1. To watch Italian diplomatic communications and their security.

2. To provide the Italian Ministry of Foreign Affairs and the Italian missions abroad with suitable means of communication.

3. To keep the Foreign Office, State Department and Allied Control Commission informed of the contents of Italian telegrams.

4. To keep GC&CS and the corresponding US organisation informed regarding Italian cyphers and lines of communication.

The Italian Foreign Office, now reestablished in Rome, had been informed through the Allied Control Commission of items 1 and 2, and no doubt suspected 3. Contact with its cypher bureau was established at once on the amicable footing that our control was a necessity while operations were impending. Each party was well aware that it was dealing with its professional opposite numbers who had obligations which would be veiled throughout the official dealings by a good-humoured reticence.’