The aim of the IACR Ph.D. database is twofold. On the first hand, we want to offer an overview of Ph.D. already completed
in the domain of cryptology. Where possible, this should also include a subject classification, an abstract, and
access to the full text.
On the second hand, it deals with Ph.D. subjects
currently under investigation. This way, we provide a timely
map of contemporary research in cryptology.
All entries or changes need to be approved by an editor. You can contact them via phds (at) iacr.org.
Jean Monnerat (#549)
Topic of his/her doctorate.
Short Undeniable Signatures: Design, Analysis, and Applications
undeniable signatures, short signatures
Year of completion
Digital signatures are one of the main achievements of public-key cryptography
and constitute a fundamental tool to ensure data authentication. Although their
universal veri?ability has the advantage to facilitate their veri?cation by the recipient, this property may have undesirable consequences when dealing with sensitive
and private information. Motivated by such considerations, undeniable signatures,
whose veri?cation requires the cooperation of the signer in an interactive way, were
This thesis is mainly devoted to the design and analysis of short undeniable signatures. Exploiting their online property, we can achieve signatures with a fully
scalable size depending on the security requirements. To this end, we develop a
general framework based on the interpolation of group elements by a group homomorphism, leading to the design of a generic undeniable signature scheme. On
the one hand, this paradigm allows to consider some previous undeniable signature
schemes in a uni?ed setting. On the other hand, by selecting group homomorphisms
with a small group range, we obtain very short signatures.
After providing theoretical results related to the interpolation of group homomorphisms, we develop some interactive proofs in which the prover convinces a
veri?er of the interpolation (resp. non-interpolation) of some given points by a
group homomorphism which he keeps secret. Based on these protocols, we devise
our new undeniable signature scheme and prove its security in a formal way. We
theoretically analyze the special class of group characters on Z_n^*
algorithmic aspects of the homomorphism evaluation, we compare the efficiency of
different homomorphisms and show that the Legendre symbol leads to the fastest
signature generation. We investigate potential applications based on the speci?c
properties of our signature scheme. Finally, in a topic closely related to undeniable
signatures, we revisit the designated con?rmer signature of Chaum and formally
prove the security of a generalized version.