I've seen a lot of ciphers with variants that use 80-bit keys, like Grain, Trivium, KLEIN, KATAN & KTANTAN, Piccolo, PRESENT, RC4, Skipjack, and TWINE. Some of these designs are younger than six years old, making me wonder if an 80-bit key size is "secure", be it against brute force attacks or as a buffer in the case of weaknesses in a cipher's design. Is 80-bit security not enough anymore? Is it only on the edge of being insecure? If it is on the edge, by what time will 80-bit keys be obsolete?

  • $\begingroup$ secure is relative, I consider 128-bit insecure for a variety of use cases, and just fine for others, but have NEVER considered 80 secure $\endgroup$ – Richie Frame Dec 23 '17 at 0:35
  • $\begingroup$ @RichiFrame Even for lightweight cryptography? $\endgroup$ – Melab Dec 23 '17 at 11:50