# AES-128 with weak key

Doing malware research (simple crypto locker) I found out that it uses AES-128 with weak key - every one of the sixteen bytes is represented by (a-z,A-Z,0-9). Thus simple brute-force attack should iterate through $62^{16}$, that is approximately $2^{96}$ keys. I have a file before encryption and after.

Is it feasible in modern world to brute-force it to find a key with a budget of $3-4k? • Can you post the asm code or pseudocode for the key generation? – jonasl Sep 22 '14 at 6:21 • Note that the term "weak key" also has a different meaning in the cryptographic world. It may also refer to a key that is inherently weak for the specific algorithm. This key is not; it's just badly defined/generated. – Maarten - reinstate Monica Sep 22 '14 at 14:06 ## 1 Answer No, it's not. Here, Bruce Schneier estimates the cost of finding a SHA-1 collision. He estimates that this would require approximately 274 CPU cycles and cost about \$700 thousand in 2015. Trying 296 AES keys would require approximately 2100 CPU cycles and cost about \\$50 trillion.

• Although I am pretty sure that the calculations are approx. in the right ballpark - i.e. not feasible - , it may be a bit tricky for readers to jump from SHA-1 collisions to AES key brute forcing. – Maarten - reinstate Monica Sep 22 '14 at 14:04