No account, no cloud storage, no subscription, no bundled "vault" you have to trust. One window, two gestures, and three real ciphers doing the work underneath.
Ultra mode runs AES-256-GCM, then ChaCha20-Poly1305, then an ISAAC⁺ keystream. Each is keyed independently via HKDF-SHA256, so breaking one buys an attacker nothing. The outer layers can only raise the ceiling; they never lower it below AES.
Argon2id runs at RFC 9106 parameters: 64 MiB, 3 iterations, 4 lanes. That turns a GPU cracking farm into an expensive way to guess slowly. Get the password wrong and Cyh Cipher tells you immediately, before it ever asks where to save.
Files stream through the cipher in 1 MiB chunks across every core your Mac has. Output goes to a temporary file and is only renamed into place after a clean write, so a crash or a force-quit never leaves a broken file behind.
fsync, rename.If you forget your password, the file is gone. That's what strong encryption means.
There is no recovery key, no backdoor, no support line that can help. The sandbox grants Cyh Cipher exactly one entitlement: read/write access to the file you choose. Nothing else. No network access, no account, no analytics.