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They are talking about asymmetric encryption, which is what you always need when communicated with someone else. Symmetric encryptions like AES also work withou
by _fizz_buzz_ 5y ago
They are talking about asymmetric encryption, which is what you always need when communicated with someone else. Symmetric encryptions like AES also work without one-way functions.
- deleted 5y ago[deleted]
- thiagoharry 5y agoNo, the security of AES assumes that AES is an one-way function. Otherwise, if AES is not one-way, one could decrypt it easily reversing the function. Symmetric encryption usually assumes the existence of one-way functions, but there are indeed some rare exceptions. The one-time pad is a construction with unconditional security and is secure even if one-way functions do not exist. Of course, it requires the assumption that each person will not reuse the key more than once. And without one-way functions, you also would never be able to exchange the keys securely using any computer network.
- _fizz_buzz_ 5y agoBut you can reverse AES! You obviously need the secret key, but it's trivial to reverse the steps of encryption (it's actually a bit tricky to get all the steps correctly, but you can easily google how to do it, tons of example impelentations and lecture notes online). There are a bunch of online tools that demonstrate it such as: https://www.devglan.com/online-tools/aes-encryption-decryption https://www.devglan.com/online-tools/aes-encryption-decrypti...
- rocqua 5y agoAes is a one-way function if you consider the key part of the arguments to the function.
- Aardwolf 5y agoOne requirement for one way functions is to not easily find a preimage. With AES output you could decrypt it with a wrong key, get wrong plaintext, but they're still a valid input combination giving this same AES output
- jkhdigital 5y agoDifferent key = different function, so you have not inverted the original function and thus have not found a preimage.
- rocqua 5y agoFair point! I guess it's a one-way function given only the key as input with a fixed ciphertext. Incidentally if you use AES in a AED mode (like AES gcm) then it would be a one-way function but that is more about the MAC.
- jkhdigital 5y agoActually they aren't talking about asymmetric/public-key encryption, but rather "efficient" symmetric encryption (and related primitives) where the key size is (asymptotically) smaller than the plaintext size.