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Uncrackable encryption has existed for ages, it's known as the one-time pad. Unless you have access to the key then you stand no chance of reading the original plain text. Its big weakness is key generation and distribution, which has to be done via secure channels in advance, unlike public key encryption, which has easier key distribution but is less secure (depending on the amount of compute power available). Of course, one advantage of the one-time-pad is that in theory it is possible to easily create a spoof key to produce a harmless plain text.