# Security Policy
If you discover a security issue in `fcrypt`, please report it privately and do not open a public issue.
`einspiegel@protonmail.com`
## Reporting
1. Provide a clear description of the issue.
2. Include reproduction steps and affected version(s).
3. Include impact details (data exposure, integrity risk, etc.).
## Scope
This project focuses on:
- correctness of encryption/decryption behavior
- integrity guarantees and tamper detection
- safe error handling without leaking sensitive data
## Opaque format
New encrypted files use the opaque container format. Files do not start with magic bytes, a cleartext version, cleartext algorithm identifiers, or cleartext recipient identifiers. Format metadata is authenticated and encrypted in the manifest, and payload chunk indexes use `u64` nonces.
## Legacy compatibility
Opaque files authenticate empty inputs with an AEAD tag. Legacy pre-opaque containers are not auto-detected by the current decrypt path because the format intentionally avoids cleartext headers.
`fcrypt` `0.3.0` does not provide backward compatibility for files encrypted by `fcrypt` `0.2.0` or earlier. Use `fcrypt` `0.2.0` to read those old files.