TY - JOUR AU - Farshim, Pooya AU - Orlandi, Claudio AU - Rosie, Razvan PY - 2017/03/08 Y2 - 2024/03/28 TI - Security of Symmetric Primitives under Incorrect Usage of Keys JF - IACR Transactions on Symmetric Cryptology JA - ToSC VL - 2017 IS - 1 SE - Articles DO - 10.13154/tosc.v2017.i1.449-473 UR - https://tosc.iacr.org/index.php/ToSC/article/view/604 SP - 449-473 AB - We study the security of symmetric primitives under the <em>incorrect</em> usage of keys. Roughly speaking, a <em>key-robust</em> scheme does not output ciphertexts/tags that are valid with respect to distinct keys. Key-robustness is a notion that is often tacitly expected/assumed in protocol design — as is the case with anonymous auction, oblivious transfer, or public-key encryption. We formalize simple, yet strong definitions of key robustness for authenticated-encryption, message-authentication codes and PRFs. We show standard notions (such as AE or PRF security) guarantee a basic level of key-robustness under honestly generated keys, but fail to imply keyrobustness under adversarially generated (or known) keys. We show robust encryption and MACs compose well through generic composition, and identify robust PRFs as the main primitive used in building robust schemes. Standard hash functions are expected to satisfy key-robustness and PRF security, and hence suffice for practical instantiations. We however provide further theoretical justifications (in the standardmodel) by constructing robust PRFs from (left-and-right) collision-resistant PRGs. ER -