"How long have you been worried about this?" he asked
"Since Tisler."
Arthur opened his desk drawer and pulled out a small bottle of Scotch. He poured us both a small measure in his coffee cups.
"Have you told Roger?"
I told him that I had raised the issue twice before, once after Tisler, and once after Lonsdale. Both times I had been stifled. He seemed surprised.
"I suppose you've guessed what I'm doing?"
"It's Mitchell, isn't it?"
"Somebody told Kim when to run," he said, hardly answering my question, "I'm sure of it. Only someone in Graham's place could have known enough to do it."
Arthur told me to see Hollis myself.
"Tell him we've talked, and that I suggested you see him. It's the only way."
I rang up to Hollis' office, and to my surprise got an almost immediate appointment. I took the lift to the fifth floor and waited for the green light to flash above his door. I was shown in by his secretary. Hollis was sitting upright at his desk under the bay window, working on a single file, a line of pencils on one side, each one carefully sharpened to a precise point. I advanced until I was standing a few feet from the other side of the desk. He did not look up. I waited for almost a minute in silence while Hollis' predecessors gazed balefully out at me from the wall. Still I waited. Still his pen scratched at the file.
"How can I help you, Peter?" he asked at length.
At first I stuttered badly. The last hour had been a strain.
"I've been talking with Arthur Martin, sir."
"Oh?" There was no trace of surprise in his voice.
"I have let my hair down about my worries..."
"I see..."
Still he worked on.
"I have done another analysis, sir, and he said I should come and show it to you."
"Take it over to the table, will you..."
I retreated back across the room, and sat at the huge polished conference table. Hollis joined me, and began to read in silence. Occasionally he queried a point in my analysis. But I could sense that today he was no opposition. It was almost as if he were expecting me.
"Did you know he's retiring in six months?" he asked when he had finished reading.
"Mitchell?" I asked, in genuine confusion. As far as I knew, he had at least a couple of years to go.
"He asked for it a while ago," said Hollis. "I can't change it now. I'll give you that long to prove it. You can join Martin, and I'll square it with Willis."
He handed me the file back.
"I don't have to tell you that I don't like it. You know that already. Not one word of this investigation is to leak out, understood?"
"Yes, sir!"
"You'll need to know Mitchell's background," he said, as he returned to his desk and pencils. "I'll arrange for Arthur to have his Record of Service."
"Thank you, sir."
He was already writing again as I went out.
As soon as I joined the Mitchell case, I was indoctrinated into the greatest counterintelligence secret in the Western world - the VENONA codebreak. To understand what VENONA was, and its true significance, you have to understand a little of the complex world of cryptography. In the 1930s, modern intelligence services like the Russian and the British adopted the one-time code pad system of communications. It is the safest form of encipherment known, since only sender and receiver have copies of the pad. As long as every sheet is used only once and destroyed, the code is unbreakable. To send a message using a onetime pad, the addresser translates each word of the message into a four-figure group of numbers, using a codebook. So if the first word of the message is "defense," this might become 3765. The figure 3765 is then added to the first group on the one-time pad, say 1196, using the Fibonacci system, which makes 4851. It is, in effect, a double encipherment. (The Fibonacci system is also known as Chinese arithmetic, where numbers greater than 9 are not carried forward. All cipher systems work on the Fibonacci system, because carrying numbers forward creates nonrandom distribution. )
The VENONA codebreak became possible because during the early years of the war the Russians ran short of cipher material. Such was the pressure on their communications system that they made duplicate sets of their one-time pads and issued them to different embassies in the West. In fact, the chances of compromising their communications were slim. The number of messages being transmitted worldwide was vast, and the Russians operated on five channels - one for Ambassadorial communications, one for the GRU, another for the Naval GRU, a fourth for the KGB, and lastly a channel for trade traffic connected with the vast program of military equipment passing from West to East during the war, which on its own comprised about 80 percent of total Russian messages. A set of pads might be issued to the KGB in Washington for their communications with Moscow, and its duplicate might be the trade traffic channel between Mexico and Moscow.
Shortly after the end of the war a brilliant American cryptanalyst named Meredith Gardner, from the U.S. Armed Forces Security Agency (the forerunner of the NSA), began work on the charred remains of a Russian codebook found on a battlefield in Finland. Although it was incomplete, the codebook did have the groups for some of the most common instructions in radio messages - those for "Spell" and "End-spell." These are common because any codebook has only a finite vocabulary, and where an addresser lacks the relevant group in the codebook - always the case, for instance, with names - he has to spell the word out letter by letter, prefixing with the word "Spell," and ending with the word "Endspell" to alert his addressee.
Using these common groups Gardner checked back on previous Russian radio traffic, and realized that there were duplications across some channels, indicating that the same one-time pads had been used. Slowly he "matched" the traffic which had been enciphered using the same pads, and began to try to break it. At first no one would believe him when he claimed to have broken into the Russian ciphers, and he was taken seriously only when he got a major breakthrough in the Washington-to-Moscow Ambassadorial channel. He decrypted the English phrase "Defense does not win wars!" which was a "Spell/Endspell" sequence. Gardner recognized it as a book on defense strategy published in the USA just before the date the message was sent. At this point, the Armed Forces Security Agency shared the secret with the British, who at that time were the world leaders in cryptanalysis, and together they began a joint effort to break the traffic, which lasted forty years.
Operation BRIDE (as it was first known) but later DRUG and VENONA, as it was known in Britain, made painfully slow progress. Finding matches among the mass of traffic available took time enough. But even then there was no certainty the messages on each side of the match could be broken. The codebook was incomplete, so the codebreakers used "collateral" intelligence. If, for instance, they found a match between the Washington-to-Moscow KGB channel and the New York-to-Moscow trade channel, it was possible to attack the trade channel by using "collateral," information gathered from shipping manifests, cargo records, departure and arrival times, tide tables, and so forth, for the date of the message. This information enabled the codebreakers to make estimates of what might be in the trade traffic. Once breaks were made in one side of a match, it provided more groups for the codebook, and helped make inroads on the other side.