In 1987 MI5's former Assistant Director, Peter Wright, released his autobiography. Spycatcher: The Candid Autobiography of a Senior Intelligence Officer.
It was immediately banned by the British Government. Although the Internet wasn't around to facilitate its distribution, it was trivial to obtain copies imported from Australia. As a boy, I remember seeing the publicity about it on the news and being very upset that my parents had a copy!
It is not.
The physical book is long out of print and is available second hand on Amazon.
There's a scanned and OCR'd copy of the eBook available on OpenLibrary. If you are to venture to the "deep web" (i.e. the 2nd page of Google results) you'll find plenty of ersatz eBook copies floating around.
So, what does a book about the security state in the 1950s, 60, and 70s have to do with the world today?
Here are some choice quotes which I found interesting.
Metadata and Warrants
Each major [post] sorting office and [telephone] exchange in the country had a Special Investigations Unit Room, under the control of [Major Albert] Denman, to place taps and intercept mail.
In fact, Denman was very particular about warrants. He was prepared to install a tap or intercept an address without a warrant only on the strict understanding that one was obtained as soon as possible. MI5 were, however, allowed to request a form of letter check without a warrant. We could record everything on an envelope, such as its origin and destination and the date it was sent, as long as we did not actually open it. Denman, like everyone in the Post Office who knew of the activity, was terrified in case the Post Office role in telephone and mail intercepts was discovered.
Spycatcher - page 45-46
Here we have a excellent argument about why metadata is important. Traffic analysis about which parties are communicating and can be used to build up a detailed picture of a target - even without a warrant and probable cause.
We also see that the security service has always been lax about the need to obtain warrants before intercepting communications.
Finally - I wonder if ISPs today are similarly terrified about their role in PRISM? With seemingly every major ISP, social network, and telecoms company now in the hands of the intelligence services, it seems the more things change the more they stay the same...
I had spent a lot of time researching ways in which innocuous objects, like ashtrays or ornaments, could be modified to respond to sound waves when radiated with microwaves of a certain frequency. If a system could be perfected, it promised enormous advantages. The object itself would carry no transmitter or receiver, so detection would be virtually impossible. By 1956 we had successfully developed prototypes, and decided to attempt an operation against the Russian Embassy in London.
Spycatcher - page 67
While we sit here and worry whether our phones can be used to eavesdrop on us, or wonder if an empty crisp packet can do the same - the reality is that for over 60 years MI5 has had the ability to listen in to our conversations at will.
In 1959, a new discovery was made which resuscitated VENONA again. GCHQ discovered that the Swedish Signals Intelligence Service had taken and stored a considerable amount of new wartime traffic, including some GRU radio messages sent to and from London during the early years of the war. GCHQ persuaded the Swedes to relinquish their neutrality, and pass the material over for analysis.
Spycatcher - page 186
While it is natural that wartime signals should be stored, I think it's interesting that going back over ancient data with new knowledge has been a staple of spying for years. While we may think our PGP encryption is secure now - any future attacks will render its protection useless.
Of course, storing data is somewhat pointless when the sheer volume of it means it overwhelms the capacity to analyse it.
A joint MI6/CIA team had tunneled under the Russian sector of Berlin in February 1955, and placed taps on the central communications of the Soviet Military Command.
The actual electrical taps were done by Post Office personnel. Both the CIA and MI6 were reeling under the sheer volume of material being gathered from the Tunnel.
So much raw intelligence was flowing out from the East that it was literally swamping the resources available to transcribe and analyze it. MI6 had a special transcription center set up in Earl's Court, but they were still transcribing material seven years later when they discovered that George Blake had betrayed the Tunnel to the Russians from the outset.
Spycatcher - page 47
And, even if cracked and analysed - someone has to actually make use of the material!
I was shown into a room in Northumberland Avenue which contained all the Dragon material, stacked up in dozens and dozens of dusty volumes. Incredibly, neither MI5 nor MI6 had bothered to process any of this material for its own use.
Spycatcher - page 116
With Friends Like These...
The Germans are appalled to discover
gambling spying taking place against them. Merkel is furious!
For nearly three years, between 1960 and 1963, MI5 and GCHQ read the French high grade cipher coming in and out of the French Embassy in London. Every move made by the French during our abortive attempt to enter the Common Market was monitored. The intelligence was avidly devoured by the Foreign Office, and verbatim copies of De Gaulle's cables were regularly passed to the Foreign Secretary in his red box.
Spycatcher - page 111
Yeah. We spied on friend and foe alike - and they spied on us.
I made a series of analyses of Soviet strength in 1945, based on the VENONA material. Although we broke only a small fraction of the traffic, GCHQ were able to statistically assess the total number of spies active in Britain at between 150 and 300. (The statistical analysis was conducted using methodology devised by one of the top cryptographers, I.J. Good.)
Spycatcher - page 344
Again, we see that decryption isn't necessarily needed in order to analyse data. Encrypting your email isn't enough - traffic analysis can give an excellent idea of how many people you are in communication with and the volumes of material you are exchanging.
And, in the end
There's no doubt that Spycatcher is still a highly significant book. What may have seemed somewhat dry and irrelevant when first published, has now become frighteningly prophetic. It is vital that the book is republished and that all students of security - computer or otherwise - read it and learn its lessons.
For anyone with an interest in the development of the security state - and the evolution of computerised espionage, Spycatcher is a must.
I'll leave the last words to the judgement of the Law Lords who decided whether Spycatcher should be banned.
'In a free society,' Lord Geoff said, 'there is a continuing public interest that the workings of government should be open to scrutiny and criticism.'
Lord Keith of Kinkeld said the Government's claim that anyone receiving confidential information from a Crown servant in any circumstances is bound by an obligation of confidence was 'untenable and impracticable, in addition to being unsupported by any authority'.
Lord Griffiths, chairman of the Security Commission, said: 'The balance in this case comes down firmly in favour of the public interest in freedom of speech and a free press.' But he said that a member or former member of the security services could publicly disclose his concerns only as a last resort.
Attorney General v Guardian Newspapers Ltd (No 2)  UKHL 6 (13 October 1988)
You can buy used copies of Spycatcher on Amazon.