How long should a block cipher key length should be? what key length from below numbers can be treated as safe, keeping in view the current/ future brute force capabilities.

  1. 64 bit
  2. 80 bit
  3. 96 bit
  4. 120 bit
  5. 128 bit
  6. 192 bit
  7. 256 bit
  • 3
    $\begingroup$ keylength.com $\endgroup$ – SEJPM Feb 15 '17 at 10:50
  • 2
    $\begingroup$ What research have you done? And why only consider brute force attacks? $\endgroup$ – tylo Feb 15 '17 at 13:09
  • $\begingroup$ Brute force capabilities of who? For real time crypto or for long term storage? If this is part of a lesson, give the teacher a kick to the ankle from me. Well, figuratively of course, just pointing to this comment should suffice. $\endgroup$ – Maarten Bodewes Feb 15 '17 at 13:13
  • $\begingroup$ Since it is estimated there are $2^{272}$ atoms in the known universe, and you didnt specify how far into the future, and from whom you want to keep data safe, i choose 288 bits x 2 = 576 bits. $\endgroup$ – Richie Frame Feb 15 '17 at 19:40
  • $\begingroup$ for real time as wel for future upto 50-100 years. $\endgroup$ – khan Feb 16 '17 at 10:24

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