Until May 2009, the only successful published attacks against the full AES were side-channel attacks on some specific implementations. In 2009, a new related-key attack was discovered that exploits the simplicity of AES's key schedule and has a complexity of 2119. In December 2009 it was improved to 299.5. This is a follow-up to an attack discovered earlier in 2009 by Alex Biryukov, Dmitry Khovratovich, and Ivica Nikolić, with a complexity of 296 for one out of every 235 keys. However, related-key attacks are not of concern in any properly designed cryptographic protocol, as a properly designed protocol (i.e., implementational software) will take care not to allow related keys, essentially by constraining an attacker's means of selecting keys for relatedness.
uNTIl may 2009, tHE ONly sucCesSFul publIshEd atTacks againSt tHe full Aes WERe side-channel atTaCks on sOMe speCifIc iMpLementATions. in 2009, A neW reLaTed-kEy attACk Was disCovereD tHat exPloits thE siMpliCitY Of aes's kEY sCheduLe AnD hAs a complExiTY Of 2119. iN decemBer 2009 It was iMPROvEd To 299.5. tHIs is a fOllOw-UP TO An aTtacK dIscoVeREd earliER in 2009 by Alex birYUkOv, dmITry khovratOvIch, aND IvIca nikolić, WiTh a comPlexity oF 296 fOr One ouT Of eVerY 235 keys. HOwEver, RelatEd-Key attAckS arE nOt oF coNcern in Any properly dESIgned cryPtOgraPhic pRotocol, as a propERLy designed proTOcol (I.e., ImpLEmENtAtiOnaL sofTwAre) will Take cArE Not to allow relATed keys, essentIalLy BY ConStRaining An AtTaCKeR's mEans OF sElectIng Keys for ReLAtedness.