Concept:End-to-end encryption

End-to-end encryption (E2EE) is a method of protecting communication in a way where only the sender and the intended recipient can read and decipher the communication back and forth. Importantly, the content of the communication is inaccessible to any third party, including network providers and service providers facilitating the connection or service. Law enforcement agencies and governments have accused E2EE usage of helping and enabling criminal activity, and offering wrongdoers a place to hide. They demand a 'law-enforcement only backdoor', which is, of course, impossible, as open source tools and methods to enable E2EE are readily available. =Problem of 'going dark'= Law enforcement agencies often call attention to the fact that the modern ubiquity if encryption has made it impossible to use legal tools such as warrants to monitor the communications of a person suspected of a crime. They call this 'going dark'. == An exceptionally short primer on encryption == Cryptography and encryption are vast and complex fields, far outside of scope of this wiki, however, we will aim to introduce you with the most basic terms.

Symmetric encryption
Symmetric encryption is when two parties agree on a shared method (shared secret) which allows them to modify the information they wish to protect (plaintext) in a way that the recipient will be able to undo, but another third party who does not posses the shared secret will not. For example, imagine a situation where Alice wants to secretly tell Bob what her net worth is. Prior to this however, they had agreed to add the number 3419817552058 to whatever the actual net worth is. So Alice takes her actual net worth, $22 000, and adds the shared secret, arriving at $3419817574058 (this is called ciphertext). Receiving the ciphertext, Bob takes away the agreed upon number, and arrives at the plaintext (Alice's actual net worth). A third party, Charlie, has seen and recorded the ciphertext, but without knowing how much to take away, he cannot be sure what the net worth is. This is of course a very simplistic method, but it does illustrate the core point: assuming that the shared secret is truly random and truly secret, and no operational slip-ups have happened (like Bob writing down the shared secret and Charlie finding it), the encryption is unbreakable as Charlie has no way of guessing what the shared secret is. It could be any number between 1 and infinity.

Asymmetric encryption
But what if we are unable to establish a shared secret? What if we are physically distant or have never met? This is where asymmetric (aka public key) encryption steps in. Asymmetric encryption relies upon the fact that certain mathematical processes are easy to do one way, but hard to do in reverse. Imagine if somebody asked you which two prime numbers multiply to 143. Finding the answer to that is very hard, and there is no better way than just trying by multiplying numbers that may be suitable, either in order or ones that multiply to approximately required number, until you happened to stumble into the solution. Now imagine if the number you were given is not 143, but a number that is very large, and may have a thousand digits. It is an impossible task. But, if somebody asked you to multiply 11 and 13, doing so is trivial even for school children. And if somebody gave you two very large numbers, it'd be very tedious, but it is a doable task. Thus we have a function which is easy to do in one way, but very hard to reverse. Using such one-way functions it is possible to generate a pair of keys (numbers) which do not at a glance share anything in common, but are able to reverse each other's encryption. This allows you to publish one of them publicly (hence public key) and keep the other one secret (hence secret key). Now anyone can use the public key to encrypt a message and send it to you, safe in the knowledge that only you can read it (because only you have the private key).

Key exchange
Can we combine the characteristics of symmetric and asymmetric encryption to arrive at a system which possesses the benefits of both? Yes we can. Let's go back to Alice and Bob. Imagine if Alice selects a random number, let's say, 33. The Alice encrypts it with Bob's public key and sends the ciphertext to Bob. Bob does the same, selects random number, 17, encrypts it with Alice's public key and sends it to Alice. Alice knows which number she sent (33) and has decrypted the message Bob sent and found 17 in it. Alice knows that the communication system requires them to add the two numbers, so she adds 33 and 17 and arrives at the shared secret which is 50. Bob, knowing his own number 17 and receiving 33 from Alice, adds them both up and also arrives at 50. Both Alice and Bob now know the shared secret, and anyone observing them cannot reliably guess the shared secret number. Now Alice and Bob can switch back to symmetric encryption using the shared secret, as described in the symmetric encryption section.

Implications
The key fact that the above description is meant to illustrate that encryption, including end-to-end encryption, is just maths. Same indisputable, immutable maths that tells us that 2 + 2 is 4 or 5 < 10. There's nothing magical about it, it is just an agreed upon system that two parties can use to transform their conversation into something nobody but them can understand. Another important point is that like all maths, anyone who knows and understands the principles can use the methods to their own ends. Just like you cannot prevent your enemy from using maths against you, you cannot prevent your adversary using the above methodology to communicate securely. It is a nonsensical idea that anyone could ban or outlaw maths, just as one cannot outlaw colour purple out of existence.

Backdoor?
You can modify the encryption method to allow a third party to peek into the contents of the messages, but you cannot modify it in such a way to make sure that only a specific third party has access to it, and nobody else. You can create a backdoor, but you cannot create a law-enforcement specific backdoor. A weakness, once introduced, can be exploited by anyone who knows it. Yes, you can classify the existence of the backdoor/weakness, but the question is how long can you keep that a secret from internal leakers, independent researches who may independently discover it or an adversary that may be able to throw money at the problem. Of course, once the cat is out of the bag, all the ordinary people who trusted your crippled encryption scheme have now had their private data breached, while the criminals who never trusted you in the first place and used publicly available encryption, known to be secure, are still plying their criminal trade in secret.

Define 'legitimate law enforcement use'
Defining 'legitimate law enforcement use' is one of those issues that start off very easy but become murky very quickly. On the extremely clear side we have uses which no reasonable person would opposed to, such as protecting children from predators or protecting victims we know to be in imminent danger of violence. But, as usual, the road to hell is paved with good intentions. Should we use it to spy on organised crime? Probably. Known perpetrators of domestic violence? If we have probable cause, yeah, sure. But what if we don't? Should we use it against our country's enemies, foreign and domestic? Probably. But how do we define an enemy? Is does the definition of the enemy include an opposing party I disagree with which seeks to take our country in a fundamentally different direction we disagree with? Do we spy on our allies, even if we don't suspect them of dishonesty, just to be sure? Do we spy on violent protesters looting and burning public property? Do we spy on peaceful protesters? How do we separate the two as they're often intermingled? Do we spy on a political opponent we suspect of breaking a law? Where does this end? The grim reality is that it does not. These tools, once available, trickle down to lower and lower levels of law enforcement until they're used to prosecute trivial offences and fines.