Entité de rattachement
Le CEA est un acteur majeur de la recherche, au service des citoyens, de l'économie et de l'Etat.
Il apporte des solutions concrètes à leurs besoins dans quatre domaines principaux : transition énergétique, transition numérique, technologies pour la médecine du futur, défense et sécurité sur un socle de recherche fondamentale. Le CEA s'engage depuis plus de 75 ans au service de la souveraineté scientifique, technologique et industrielle de la France et de l'Europe pour un présent et un avenir mieux maîtrisés et plus sûrs.
Implanté au cœur des territoires équipés de très grandes infrastructures de recherche, le CEA dispose d'un large éventail de partenaires académiques et industriels en France, en Europe et à l'international.
Les 20 000 collaboratrices et collaborateurs du CEA partagent trois valeurs fondamentales :
• La conscience des responsabilités
• La coopération
• La curiosité
Référence
2025-38555
Transciphering is a cryptographic technique that re-encrypts data from one scheme to another without an intermediate decryption step. This process drastically reduces the overhead induced by the size of homomorphic ciphertexts during their transmission and storage.
The core idea of transciphering is to convert data encrypted with a classical symmetric encryption scheme into a Homomorphic Encryption (HE) scheme.
How Transciphering Works ?
Consider a scenario with a plaintext message m, a symmetric scheme SYM with key k, and a Homomorphic Encryption scheme HE with a public key pk.
The message is initially encrypted as SYM.Enc_k(m).
Transciphering uses the evaluation capability of the HE scheme to perform the symmetric decryption process entirely within the homomorphic domain. The process requires the symmetric key k to be encrypted under HE public key, HE.Enc_pk(k).
By using the homomorphic evaluation key evk, the result is a message encrypted directly under HE public key pk:
HE.Eval_evk(SYM.Dec(HE.Enc_pk(k), SYM.Enc_k(m))) = HE.Enc_pk(m)
The final result, HE.Enc_pk(m), can now be used for homomorphic computation.
Application and Goal
The primary application of transciphering is to allow clients to outsource the cumbersome process of homomorphic encryption to a more resource-abundant party, such as a Cloud or Edge server (often modeled as an honest-but-curious third party).
This approach lets clients use a fast symmetric scheme for initial encryption and data transmission, relying on the server to perform the resource-intensive transciphering step before homomorphic computation begins.
Internship Focus
During this internship, we will revisit and analyze transciphering techniques, focusing on recent advances
and optimizations in Homomorphic Encryption schemes to improve efficiency and performance. For example, we will study AES transciphering.
Je me crée un espace candidat
