Encrypted broadcasts during the night

[Tractorfan]

Hi,
Before the advent of T'intynet and 24hour broadcasting, I remember that there used to be encrypted programmes outside normal broadcasting hours. They were usually on BBC2 in the wee small hours and were for the benefit of the medical profession. The line sequence was scrambled, and the sound was a high pitched crackle.
I'm curious about how this was decrypted. Did subscribers have some sort of set top box that was password protected? When analogue satellite first arrived, I think the same encryption was used for the adult channels (not that I know about such things, of course!)
Cheers, Pete

[8 Tracker]

Could this be BBC Select, in which you needed a "Selector" (the Beeb's name for a decrypter) to un-scramble the signals. I remember it being advertised for a while in the 90s. The project was very short lived and a large number of the Selectors turned up on the surplus market. Can't remember what was actually transmitted though.
Mark.

[Tractorfan]

Hi,
Yes, that's it. I couldn't remember the name. The ones I remember seeing listed were for medics.
Cheers, Pete

[hamid_1]

Yes I also remember the BBC scrambled broadcasts from the early 1990s.

The scrambling system was called VideoCrypt-S (the S stood for "Shuffle"). Sky TV used VideoCrypt at the time, but their version worked slightly differently. Sky's version (the first) divided each line of the picture into two, then transmitted the two halves in the wrong order. Each line was cut in two at one of 255 pseudo-random points, so the two halves weren't always the same size. Both halves of each line were received and stored in the decoder. An authorised "smart" viewing card would give a "seed" number which would generate an identical pseudo-random number sequence. The decoder used this to reassemble the two wrong halves of the scrambled line. If the sequence was correct, the line would be played back from the decoder in the same order in which it was encrypted. The viewing card contained a microprocessor and software which generated the numbers for the decryption sequence. It wasn't easily "hacked".

The BBC tested Sky's VideoCrypt system, which was the most secure at the time, but they found an unexpected problem with it. With terrestrial analogue TV, "ghosting" sometimes occurs. When the two halves of each randomly-cut line were reassembled in the VideoCrypt decoder, the "ghosted" part of the signal got reassembled randomly too, and it looked like noise on the picture. Eventually the BBC came up with a variation which stored a whole frame of the picture and transmitted all the lines in pseudo-random order ("shuffled"). This must have made the decoder more expensive, as it would have needed to store a whole frame instead of just one line. The decoder also had facilities to start and stop a video cassette recorder, because the programmes were broadcast overnight after "closedown". I guess the high cost of the equipment resulted in only a small number of subscribers, and it wasn't economically viable in the end. It was probably cheaper to copy and post video tapes to those people who were interested in the programmes.

The sound was "encrypted" too. The signal was inverted, giving a whispering sound on ordinary TVs. Despite the encryption, it was possible to work out roughly what was going on in the programme. Most of the programmes were aimed at doctors.

[lesmw0sec]

Interesting - first I had heard of this. My first question would be, what was so confidential about the programmes and secondly, why was a publicly financed broadcaster permitted to encrypt?

[AidanLunn]

Originally Posted by lesmw0sec

Interesting - first I had heard of this. My first question would be, what was so confidential about the programmes and secondly, why was a publicly financed broadcaster permitted to encrypt?

If it was for the medical profession, then I would guess it was encrypted because otherwise people may see the items on screen and self-diagnose any illnesses or try to perform treatment themselves, without consulting a medical professional. That answers both points, I think.

[Tractorfan]

Hi,

I think it was a subscription service for the training of doctors, and the BBC just supplied the means of broadcasting this specialist content.

My wife used to be a nursing Sister in Chester and through her I met quite a few doctors. Pity I didn't think to ask them if the BBC Select late night transmissions played any part of their training. Doh!

Back in the sixties, my Mum (not a medic) loved watching "Your Life In Their Hands" which showed surgical operations. It was in monochrome, but still made me cringe!

Fascinating replies from our learned forum members so far. Many thanks.

Cheers, Pete

[arjoll]

Originally Posted by hamid_1

With terrestrial analogue TV, "ghosting" sometimes occurs. When the two halves of each randomly-cut line were reassembled in the VideoCrypt decoder, the "ghosted" part of the signal got reassembled randomly too, and it looked like noise on the picture.

That's interesting - Sky NZ used Videocrypt on their subscriber service (4 1/2 channels on UHF - the 1/2 channel was a shared Discovery (encrypted) and horse racing (FTA) on channels owned by the NZ Racing Board. I hadn't heard of any issues with ghosting, although we only had Sky for a couple of years in the mid 90's and Invercargill doesn't really have issues with ghosting. Sky's sound wasn't encrypted.

[emeritus]

One of the six terrestrial national broadcasters in France used to encrypt some of its programmes in this way.

[hamid_1]

I've done a search and found a bit more information:

BBC Select on Wikipedia

TV ARK has some clips of BBC Select, including a trailer describing the service, and clips of BMTV (British Medical Television) encrypted. Scroll down the page to see them. The BMTV clip is dated 1989 which pre-dates the start of BBC Select. The scrambling looks different and more basic - it looks like each line is shifted left or right by a small amount.

Sky UK didn't encrypt the sound on their VideoCrypt broadcasts, either.

The BBC Select subscription service didn't really take off, but the idea lives on in the form of Top-Up TV Anytime. Top-Up TV originally began broadcasting 'live' Pay-TV channels, just like the former ONdigital service, but the success of Freeview squeezed them out of prime-time and into the small hours. They now use unused airtime on one of the commercial Freeview multiplexes. Subscribers have a special set-top box with a hard drive and smart card. The box automatically records the encrypted programmes sent overnight; the subscriber can then view them at their convenience. Some of you may have noticed the TopUp TV channels appearing on your Freeview box, but no picture is displayed unless you have the special TopUp TV decoder box, which also works as a Freeview recorder.

[ntscuser]

Originally Posted by hamid_1

The BBC Select subscription service didn't really take off, but the idea lives on in the form of Top-Up TV Anytime.

I've often seen it called another name which I can't repeat here!