Penumbra-FHE is research/prototype-grade software. It is not audited production cryptography. Do not use it to protect real secrets without an independent security review.

The privacy promise (PROJECT.md §11):

• The client holds the secret key and performs encryption/decryption.
• The server holds only the public evaluation/server key and the plaintext model weights. It runs the entire forward pass on ciphertext and never sees the plaintext input or output.

What this means in practice:

• Confidentiality of the input/output rests on the security of the underlying TFHE scheme as implemented by tfhe-rs and the chosen parameter profile. Penumbra-FHE ships a secure default profile and does not let users hand-roll insecure parameters.
• The model weights are not secret from the server — they are plaintext. Penumbra-FHE protects the data, not the model.
• This project does not (yet) defend against side channels, malicious-server result tampering, or traffic analysis. Integrity/verifiability is out of scope for now.

The default parameter profile is taken from tfhe-rs's vetted parameter sets. Parameter tuning (Phase 10) optimizes speed within a fixed security level — security is never traded for performance silently.

If you discover a security issue, please report it privately rather than opening a public issue:

• Use GitHub private vulnerability reporting on this repository, or
• Email the maintainer directly.

Please include a description, reproduction steps, and the potential impact. We will acknowledge receipt and work with you on a coordinated disclosure.

Note: cryptographic weaknesses in the underlying TFHE scheme or in tfhe-rs itself should also be reported upstream to the tfhe-rs project.