Cryptographic Filters

So, you want to be a secret agent? You may want to use these filters to encrypt and hide your information.

## Digital Signature

Digital Signature lets you make or read an invisible signature in the image. In order to read a signature just press the Read button.

If you want to create a signature, you have to fill in the information in the dialog and press the Write button. Then, you'll need to save the image in a non-
destructive format like TIFF. If you save it as a JPEG the signature will be destroyed.

The option Restricted image distribution will create a signature that states that your image is not free for distribution. The Adult contents option will create a signature stating that the image has adult contents.

## Encrypt & Decrypt

| Encrypt makes it possible to encrypt your images, so no one besides yourself can see them. To encrypt the image, bring up the filter and type in a Password. To decrypt an image, bring up the filter again, type in your password and the image will be decrypted.

The author of this filter, Daniel Cotting, warns that he can provide no guarantees that this filter will work (but for us at Frozenriver, this filter has worked just fine). Remember not to save the image in a destructive file format, such as JPEG.

You can enable backward compatibility with the 1.0 versions of this plug-in by clicking on the appropriate checkbox, but we suggest that you stick with 2 and not enable this feature unless you have images that are encrypted with the 1.0 version.

You can also enable the plug-in to remember your password, but don't forget that passwords are best kept in your own mind where no one can see them.

## Gimp Mask

Gimp Mask works by masking the entire image or selected parts of it. Unmasking is performed by running the filter once again on the selected area, using the correct code word for CP masks or by reversing the direction for MEKO masks. In most cases, you also have to fine-tune the Offset coordinates on the Adjustment tab to get the two masks to fit.

Use the Rectangle selection tool when specifying the mask area. Other selection shapes may not create the mask area properly. When you reselect the masked area (in order to unmask it), an overlap of up to seven pixels is acceptable. This means that it's OK to make a slightly bigger selection to cover all of the mask. If you should fail to get a perfect fit when you reverse the masking process, click on Cancel and try again, this time with a smaller selection.

Note that the CP code is not compatible with JPEG files, so if you're using the JPEG file format, you should choose another mask type.

## Stegano

The Stegano filter lets you hide or read a hidden file inside your image. To read the hidden file, press Read. To hide a file, press Write and then Browse (to find the file). There is no restriction concerning the file type that you want to hide.

Remember that if you want to hide a big file, you'll need to use a big image. And just like with the other encrypt filters, you can't save your image in a destructive file format like JPEG. This filter is perfect for secret agents like 007. ;-)

Frozenriver Digital Design http://www.frozenriver.nu Voice: +46 (0)31 474356 Fax: +46 (0)31 493833 support@frozenriver.com | Publisher Coriolis http://www.coriolis.com