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Lecture Notes in Computer Science
Assume that a symmetric encryption scheme has been deployed and used with a secret key. We later must change the encryption scheme in a way that preserves the ability to decrypt (a subset of) previously encrypted plaintexts. Frequent real-world examples are migrating from a token-based encryption system for credit-card numbers to a format-preserving encryption (FPE) scheme, or extending the message space of an already deployed FPE. The ciphertexts may be stored in systems for which it is notdoi:10.1007/978-3-319-56614-6_17 fatcat:akvjku2itnhtrdglfi2jnltuea