历史与人物fabiensanglard.net
Discret 11：80 年代法国的电视加密系统
Discret 11, the French TV encryption of the 80s
2020 — 2022，它一次次回到首页
黑点是上首页（≥ 50 分）的那次投稿，空心点是没冲上去的投稿，点越大分数越高。
导读
Fabien Sanglard 详解 1980 年代法国 Canal+ 付费电视台使用的 Discret 11 图像扰频系统：它通过逐行延迟/位移画面来让未订阅者看到扭曲图像，配合解码器还原。文章拆解了编码原理、解码盒的硬件实现，以及这套方案是如何被逆向和破解的。
为什么经久不衰：它把一个已消失的模拟时代技术讲得透彻，既是有趣的逆向工程案例，也让人理解现代条件接收系统之前的"加密"究竟有多脆弱。
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用相邻行相关性暴力搜索旋转偏移即可破解这类行旋转扰频。
这套系统听起来和 VideoCrypt 类似。法国方案是延迟行；VideoCrypt 则是把每一显示行按伪随机数生成的偏移量循环旋转。解码时硬件要把该行缓存进一小块（对 80 年代而言）高速 RAM，再用密钥导出的数字决定从哪个偏移开始输出到电视，到末尾再绕回开头。我之所以知道这些，是因为第一份工作里我们做过实验，看能否不用密钥重建加密图像——其实很容易，因为相邻行高度相关，只要把每行试遍 256 种旋转、与上一行比较取差异最小的即可。当然我们的系统太慢，无法实时解码（那是 90 年代初），还有些其他问题。
rwmj查看英文原文
The system sounds similar to VideoCrypt. The French system delays lines. VideoCrypt worked by rotating each display line by a number derived from a PRNG. To decode the line the hardware had to buffer the line into a small piece of fast (for 1980s) RAM, and then using a number derived from the key would send the line to the TV starting at that offset and at the end wrapping around to the beginning. I know all this because in my first job we did a bit of experimentation to see if it would be possible to reconstruct the encrypted images without the key, and in fact it was quite easy because images are very highly correlated from one line to the next, so you just had to rotate each line through each of the 256 combinations and compare it to the previous line, and pick the one with the least difference. Although our system was far too slow to decode a live feed (this would be early 90s), and had some other problems. I didn't explain this very well - the Wikipedia page has a better explanation: https://en.wikipedia.org/wiki/VideoCrypt
亲历回忆：没声音根本没法看，用设备序列号参与运算是当时不错的思路。
在比利时长大，80、90 年代我也记得 Canal Plus 和它的加密方案——还徒劳地试着照看不误地看完一部电影，当然没有声音，那纯属徒劳。我一直好奇解码是怎么做的，在当时把设备序列号纳入计算是个好主意。这也让我想起美国 DirecTV 打击盗版、在"黑色星期日"一次性端掉大批盗版者的故事。
philjohn查看英文原文
Growing up in Belgium in the 80s and 90s I also remember Canal Plus and their encryption scheme - and trying (rather fruitlessly) to watch through a movie regardless - but of course, without the sound, that was a fool's errand. I always wondered how the decoding worked, and for its time, using the serial number of the equipment as part of this calculation was a good one. Also brings to mind the stories in the US of DirecTV pirating and how they put a stop to scores of pirates on Black Sunday - https://blog.codinghorror.com/revisiting-the-black-sunday-hack/
八位数字派生六个密钥，源于从未启用的分级订阅设计。
"用户输入的八位数字实际上产生的不止一个密钥，而是六个。因为系统有个（从未启用）按等级划分的受众功能，用来把会员细分到电影、体育、纪录片等等。""等等"指的就是色情 :)
nraynaud查看英文原文
"The eight digits entered by the user actually results in not one but six keys. That is because the system had a (never used) audience feature made of levels. That was to allow subdividing memberships into Cinema, Sports, Documentaries and so on." "so on." means porn :)
Canal+ 曾用数字频道复刻当年的扰频画面作怀旧彩蛋。
近几年他们在数字电视上放了一个低码率频道来模拟这种加密效果……当然不是真的频道（数字电视里加密频道直接就是黑屏），但这是个很怀旧的致敬。
hadrien01查看英文原文
For the last few years they've put a low-bitrate channel on digital television that simulates the encryption: https://www.cpchardware.com/wp-content/uploads/2016/12/Canal.png It's not the real channel obviously (with digital TV the encrypted channels are simply blacked out), but it's a nice throwback.
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