![]() ![]() ![]() There are 128 bits in a UUID, but in a "variant 1 version 4" UUID, six of those bits are fixed, so you have at best 122 bits of entropy. this might especially be an issue on non-standard / embedded browsers.įirst off UUIDs do not have 128 bits of entropy. Beware of dragons though: "There is no minimum degree of entropy mandated by the Web Cryptography specification.". If this is really something you require then there is subtle crypto now for JavaScript in browsers, use that cryptographically secure random number generator instead. Try and avoid generating UID's at the client side entirely. If it is 32 bits taken from the system clock then it is really not entropy at all, to name just one common option. I'd also be concerned about the entropy source. In that case all bets are off, because in the end the RNG is simply not cryptographically secure. ![]() Now generally you will likely not find dupes during regular use, but an adversary may simply try and see if a collision can be made. And in that case, there is a high likelihood of collisions due to the birthday bound. So if you require 128 - 4 = 124 bits and you input 32 bits, you can rest assured that the amount left is at most 32 bits. The entropy will never go higher than the amount you put in. to concatenate 4 bits of pseudo randomness at a time until you get a 128 bit number, will this really give a safe unique UUID of 128 bits? Or is the entropy in that resulting UUID much lower? getRandomHexChar() + getRandomHexChar() +. #Uuid generator javascript codeI am looking at a seemingly popular piece of JavaScript code to generate a UUID which is supposed to be a 128-bit number: function uuidv4() $ bits of entropy) like this e.g. ![]()
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