# Cryptographic key Length

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
• keylength.com – SEJPM Feb 15 '17 at 10:50
• What research have you done? And why only consider brute force attacks? – tylo Feb 15 '17 at 13:09
• 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. – Maarten Bodewes Feb 15 '17 at 13:13
• 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. – Richie Frame Feb 15 '17 at 19:40
• for real time as wel for future upto 50-100 years. – khan Feb 16 '17 at 10:24