Zweifish is a tiny file encryption application using 256-bit Twofish encryption. Twofish is one of a few ciphers included in the OpenPGP standard.

In order to encrypt or decrypt files, drag and drop them onto the file list in Zweifish or choose the files via File menu.

Then type a passphrase. This passphrase will be used to generate the encryption/decryption key (using the JH hash function). After typing a few characters, Zweifish displays a four-color visual hash. These colors change as you type. The specific color combination when you complete the passphrase is important. The same passphrase always generates the same color combination. This enables you to detect and correct a mistyped passphrase by detecting a change in the color combination.
Press the Encrypt or Decrypt button.

Zweifish encrypts/decrypts all files on the list. If successful, the file names will turn green.

If the operation failed, the file name will turn red. (Orange file names indicate successful encryption/decryption, but other minor problems. In most cases a problem with renaming the file.)
The most likely cause for a decryption failure is a wrong passphrase. If only some files decrypted correctly, press the Remove OKs button to remove the successfully decrypted files from the list and try to decrypt the remaining files with another passphrase.

Use the preferences dialog to adjust how long the last character of the passphrase is shown before being replaced by a bullet. You may also choose whether Zweifish asks for the passphrase twice when encrypting.