Titel: Chosen-Ciphertext Security from Tag-Based Encryption
Abstract:
One of the celebrated applications of Identity-Based Encryption (IBE)
is the Canetti, Halevi, and Katz (CHK) transformation from any
(selective-ID) IBE scheme into a full chosen-ciphertext secure
encryption scheme.
Since (selective-identity) IBE schemes in the standard model (i.e.,
without using random oracles) are known from previous work this
imediately provides new chosen-ciphertext secure encryption schemes in
the standard model.

This paper revisits the notion of Tag-Based Encryption (TBE) and
provides security definitions for the selective-tag case. Even though
TBE schemes belong to a more general class of cryptographic schemes
than IBE schemes, we can show that (selective-tag) TBE schemes are a
sufficient primitive for the CHK transformation and therefore imply
chosen-ciphertext secure encryption schemes.

We construct efficient and practical TBE schemes and give tight
security reductions in the standard model from the Decisional Linear
Assumption.
In contrast to all known practical IBE schemes our TBE scheme does not
make use of pairing operations. Instanciating the CHK transformation
with our TBE scheme results in an encryption scheme whose decryption
can be carried out in a single multi-exponentiation (compared to one
pairing plus one multiplication with the fastest IBE).

Furthermore, we show how to apply the techniques gained from the TBE
construction to directly design a new Key Encapsulation Mechanism.
Since we can avoid the CHK transformation the scheme results in
improved efficiency.