On tolerant cryptographic constructions

Cryptographic schemes are often constructed using multiple component cryptographic modules. A construction is tolerant for a (security) specification if it meets the specification, provided a majority (or other threshold) of the components meet their specifications. We define tolerant constructions, and investigate 'folklore', practical cascade and parallel constructions. In particular, we show that cascading encryption schemes provides tolerance under chosen plaintext attack, non-adaptive chosen ciphertext attack (CCA1) and a weak form of adaptive chosne ciphertext attack (weak CCA2), but not under the 'standard' CCA2 attack. Similarly, certain parallel constructions ensure tolerance for unforgeability of Signature/MAC schemes, OWF, ERF, AONT and certain collision-resistant hash functions. We present (new) tolerant constructions for (several variants of) commitment schemes, by composing simple constructions, and general method of composing tolerant constructions. Our constructions are simple, efficient and practical. To ensure practicality, we use concrete security analysis (in addition to the simpler asymptotic analysis).