Convergent encryption is a cryptographic primitive introduced by Douceur et al. (Douceur, et al., 2002), attempting to combine data confidentiality with the possibility of data deduplication.
Convergent encryption of a message consists of encrypting the plaintext using a deterministic (symmetric) encryption scheme with a key which is deterministically derived solely from the plaintext. Clearly, when two users independently attempt to encrypt the same file, they will generate the same ciphertext which can be easily deduplicated. Unfortunately, convergent encryption does not provide semantic security as it is vulnerable to content-guessing attacks.
In TREDISEC, we aim at designing solutions for privacy preserving data deduplication that do not rely on fully trusted entities; they will rather leverage novel and innovative mechanisms to ensure that only the data owner can disclose the content of its data.