Black Box Cryptanalysis of AES128
2026-08-24 • Cryptography and Security
Cryptography and Security
AI summaryⓘ
The authors explore a method to crack the AES128 encryption by using a technique called Local Inversion with access only to the encryption process itself (a black box). They show it is practically possible to recover up to 80 unknown bits of the key if the rest are known, and then use these results to predict how to recover the full 128-bit key through a brute force search combined with efficient verification. Their approach suggests the full AES128 key can be found in a reasonable time under a known plaintext attack. They also propose that their method is broadly applicable to analyzing other strong encryption systems.
AES128Local InversionKnown Plaintext AttackKey RecoveryBlack Box ComputationCryptanalysisBrute Force SearchEncryptionPolynomial TimeForward Encryption Map
Authors
Virendra Sule, Kunal Telangi
Abstract
This paper presents computational results of cryptanalysis of AES using the Local Inversion by Black Box computations of the forward encryption and utilizes these results to develop a practically feasible approach for the key recovery of the full scale AES128 under Known Plaintext Attack (KPA). It is shown that complete recovery of unknown key bits is possible upto $80$ bits in a practically feasible time and memory in random KPA situation by sequential computation when remaining $48$ bits are known. The results of key recovery in $64$, $72$ and $80$ bit unknown cases are extrapolated to predict the period of the iterative sequence generated in the local inversion approach for the full $128$ bit unknown key case and a strategy is proposed to search the actual period by brute force parallel search of the sequence period with $10$ free bits defining the search space. Then it is shown that the actual key can be verified in polynomial time by fast powering of the forward encryption map. Hence this strategy shows that the key recovery problem for AES128 under KPA has a high chance of success in practically feasible time. Local inversion approach to cryptanalysis using black box computations is a universal method applicable to a vast variety of key recovery and map inversion problems. Hence the results presented in this paper are representative of estimates of cryptanalysis of other ciphers which can be considered almost as strong as AES128 as encryption functions.