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Examining his claims about "Thundercloud": You can use it with "any existing software, operating system, or device" (a massive amount of effort---by whom?) Has its "own cryptographic language that is completely independent of any existing security technology" (this is a negative thing: abandoning the entire knowledge base of cryptography is incredibly ...


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Yes, he is full of crap. If you go to KeyLength, you can compare key lengths for different cryptosystems and see how long they're expected to be secure for. It's just a performance vs security tradeoff that implementers make. Most people don't see the point in schlepping around megabytes of key material for cryptosystems that are expected to be secure ...


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For the symmetric key, you can approach this problem as a complete graph with order 1000. With the vertexes representing people and the edges representing the symmetric keys. Then each vertex would have degree 999 and, applying the Handshaking lemma, the number of edges would be: (1000 * 999)/2 = 499500 So they would need 499500 symmetric keys to have a ...


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Another alternative would be to share the same key pair between all the users devices e.g. using a QR code generator and scanner within the app. The first device would generate a QR code representing the key pair and the other phone would read it through its camera. Additionally a password based encryption can be applied to the key pair to avoid easy ...


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If the number of phones will not be "large," the answer is simple: encrypt each message with a session key, then encrypt the session key to each phone's public key and stick the list of wrapped keys on the front of the message. Each phone finds its own wrapped key, unwraps it, and decrypts the message. If you're looking for a good algorithm, might I suggest ...


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A simple solotion could be that all phones need to have the same pre-shared key. The pre-shared key could be downloaded once at first run, maybe from a password protected httpS site, or maybe from a url that delivers an encrypted and signed file with private/public key. Then the pre-shared key is used on all phones, and it is used to encrypt by the sender, ...


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There are many types of weak keys, some of them make it vulnerable to chosen plaintext attack, some of them may leak some statistical properties through the plaintext, some keys generate same subkeys for multiple rounds of an algorithm etc. See https://en.wikipedia.org/wiki/Weak_key . Keys are usualy generated randomly. The randomness is tightly connected ...


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What you're looking for is called a key derivation function, and more specifically a key stretching function. A key derivation function takes some variable-size material and turns it into a fixed-size key in a deterministic way, such that calling the same function on the same input yields the same key, and the original material cannot be reconstructed from ...



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