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As you probably know, many governments are planning on banning strong encryption, not heeding the advice of security experts.

My question is, has this ever been tried in the past, and were they successful or not?

Looking around, there's the forced disclosure of encryption keys in the UK, the ban on cryptographic export in the US, and various failed key-escrow systems like the clipper chip. But I'm interested in if there was ever an authority that explicitly and actively banned cryptography, and the rationale and context behind it. I'm particularly interested in things further back than recent history, but for the sake of people reading this question later, please don't exclude relatively recent events.

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    Google "crypto wars" – SEJPM Nov 4 '16 at 12:56
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    To be fair, I could see where someone who isn't an expert on this subject might not know the term "Crypto wars" to google for. When I tried googling for terms that were in the question, the answers weren't very comprehensive, and this question was the third hit. So it might be worth actually answering here. – T.E.D. Nov 4 '16 at 16:31
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    France doesn't ban cryptography or cryptography with keys longer than 128 bits, that is an urban myth. There are restrictions for the sale of dual use technologies or military technologies when they use military grade cryptography. There was and maybe still is a legal obligation for businesses to declare their use of cryptography (which is stupid). There are also some legal obligations for businesses selling cryptographic technologies. – Yves Nov 4 '16 at 16:47
  • en.wikipedia.org/wiki/Phil_Zimmermann As the legality of PGP was questioned, its code was reportedly (it might be a legend) written on all kinds of supports in order to be protected by the freedom of speech in the US. – Yves Nov 4 '16 at 16:53
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    Not a legend - I used to own one of the T-shirts. – Mark C. Wallace Nov 4 '16 at 17:08
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Yes.

(Note: I started writing a broad answer of various methods to make strong encryption ineffective, rather than banning it outright, and their consequences... but it quickly got off topic. Then I realized that Tor talk basically covers the whole topic and has plenty of examples of encryption bans. Watch the Tor talk at the end.)

There are few examples of "banning cryptography" outright, and it doesn't last very long in this modern age because it basically shuts down business on the Internet. The ones I know of are usually done by totalitarian regimes in the middle of civil unrest.

In times a civil unrest, a government may assert their control over the Internet by partially or totally blocking encrypted traffic. That means SSL, ssh... anything using strong encryption. This cuts off a means of people communicating without fear of spying.

For example, in Feburary 2012, Tor reported that Iran was selectively blocking SSL traffic which also had the effect of cutting off Tor, a privacy network. Plus any number of attempts to shut down or filter the Internet as part of the Arab Spring.

This is often done through deep packet inspection, basically peeking at all the traffic going by and if you spot anything that looks encrypted you block it. This doesn't just happen. It requires a great amount of planning and design work to allow centralized control of packet routing and filtering. Even if it starts innocently enough, like stopping child pornography or terrorists, that very same system can be used to censor and track dissidents.

Tor is a privacy network within a network that not only encrypts your traffic, but it prevents listeners from knowing where it came from. This can mean life or death in a totalitarian regime who might come after you just for connecting to a web site they don't like.

Even using Tor can mark you as a suspect. Tor is in a cat and mouse game to look more and more like normal HTTPS traffic. This forces government filters who want to stop Tor to also hinter legitimate encrypted traffic. This causes businesses to be unhappy which exerts pressure on the government to stop fucking with the Internet. It's cutting off your nose to spite your face.

For more examples, watch How Governments Have Tried To Block Tor. It's fascinating and very informative overview from about 2006 to 2012.

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I know a case quite a time back. During the Sino-Japanese War, an acquaintance of my family let a mechanical encryption device for the Chinese telegraph code of his design be patented. The telegraph code was in 4 decimals for each (of the more frequently used) Chinese glyphs. The device had 4 discs (out of a set of different discs, selected according to a key) each doing a mapping from 0-9 to 0-9, i.e. the 4 chosen discs were functioning as a polyalphabetical substitution. (Since there is practically no frequency analysis on the digits to be done, the scheme, if properly used with dynamic keys, could be fairly strong even today IMHO.) Shortly after the patent was granted, the authorities discovered that telegram messages encrypted with the device could not be read by them and that's bad because spies working for Japan could communicate secretly that way with telegrams. Consequently the manufacture, sale and use of the device was banned.

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