[whispersystems] Crypto

[Justin Davis]

Hi,
I was thinking about how phone calls are encrypted with AES 128 and messages with AES 256. Why do calls have a smaller key length? Does this make them less secure from an adversary like NSA?
Thanks.

[johanw]

Post by Justin Davis
I was thinking about how phone calls are encrypted with AES 128 and
messages with AES 256. Why do calls have a smaller key length? Does
this make them less secure from an adversary like NSA?
Thanks.

IMO AES256 is overkill over AES128. The weakest factor in the whole
chain is not AES-xxx, but the public key crypto. But brute-forcing the
current pubkey keys would still require more time than than the currenmt
age of the universe and more energy than the Sun will output in its
entire life so in practice we call that undoable. If someone would find
a weakness in the public key algorithm used the crypto has to change
anyway.

[Olaf Leidinger]

Furthermore, if I recall correctly, AES 256 is theoretically weaker than AES 128, since there is an attack which works better for AES 256. Yet, both are safe today.