## Oberseminar über Kryptographie

Dozent | Zeit | Raum | Erstmals am |
---|---|---|---|

Prof. A. May Prof. Eike Kiltz |
freitags, 10.45-12.00 | NA 5/64 | 16.10.15 |

Datum | Vortragende Person | Titel | Raumnummer | Beginn |
---|---|---|---|---|

16.10 | Carla Rafols | Succinct Non-Interactive Zero-Knowledge Proofs | 5/64 | 10.45 Uhr |

30.10 | Gennadij Liske | Construction of fully CCA2-secure predicate encryption schemes | 5/64 | 10.45 Uhr |

06.11 | Manuel Fersch | An analysis of DSA and ECDSA without generic groups | 5/64 | 10.45 Uhr |

## Succinct Non-Interactive Zero-Knowledge Proofs

###### In this talk I will present recent developments on the construction of SNARKs (Succint Non-Interactive Arguments of Knowledge). The term succint is used to indicate that these arguments of knowledge are independent of the size of the witness and in particular, known constructions (in the standard model but under knowledge assumptions) achieve constant-size. SNARKs have attracted a lot of attention recently due to their applcation to verifiable computation. To construct SNARKs in the standard model, Gentry, Gennaro, Parno and Raykova (EC'13) gave a new characterization of NP as Quadratic Span Programs. Danezis, Fournet, Groth and Kohlweiss (AC'14) simplified this result and introduced the notion of Square Span Programs. I will review these results, mostly concentrating on the work of Danezis, Fournet, Groth and Kohlweiss at AC'14.

## CCA-secure constructions of PE

###### We present a new framework for constructing fully CCA2-secure predicate encryption schemes with public index in composite-order groups from pair encoding schemes defined by Nuttapong Attrapadung [1]. Our construction is the first in the context of general predicate encryption which uses the technique of so-called well-formedness proofs known from public key encryption [2] and identity-based encryption [3]. The resulting constructions are simpler and more efficient compared to the schemes achieved using known generic transformation from CPA-secure to CCA2-secure schemes [4], which adapts the ideas of BCHK transformation [5]. The reduction costs of our framework are comparable to the reduction costs of the underlying CPA-secure framework of Nuttapong Attrapadung. We achieve this last result by applying the dual system encryption methodology of Brent Waters [6] in a novel way.