Targeted Ciphers for Format-Preserving Encryption.

We introduce Targeted Ciphers, which typically encipher points on domain (mathcal {X}), but can be easily modified to instead encipher points on some subset (mathcal{S}subseteq mathcal {X}). Ciphers that can directly support this domain targeting are useful in Format-Preserving Encryption, where one wishes to encipher points on a potentially complex domain (mathcal{S}). We propose two targeted ciphers and analyze their security. The first, Targeted Swap-or-Not, is a modification of the Swap-or-Not cipher proposed by Hoang, Morris, and Rogaway (CRYPTO 2012). The second, a new cipher we call Mix-Swap-Unmix, achieves the stronger notion of full security. Our targeted ciphers perform domain targeting more efficiently than the recently proposed Cycle Slicer algorithm of Miracle and Yilek (ASIACRYPT 2017).