Hermetic Stego is a steganography program which allows you to encrypt and hide the contents of any data file in another file so that the addition of the data to the container file will not noticeably change the appearance of that file. If the file which has been hidden is deleted then there is no indication that it even exists, but it can still be recovered when you need to get at it.

The program inserts data in the image file in a pseudo-random way depending on a password, and changes other bits of the image file to compensate for the modifications induced by the hidden data so as to avoid modifying statistical properties of the image file. It is thus much more secure than most steganography programs.

This program allows hiding a file of any size in one or more BMP image files, with or without the use of a user-specified stego/encryption key, so that (i) the presence of the hidden file is undetectable (even by forensic software using statistical methods) and (ii) if a user-specified stego key is used then the hidden file can be extracted only by someone, using this software, who knows that stego key.

Hermetic Stego allows (i) hiding a message file in single BMP image file or in a set of BMP images and (ii) extracting a message file from a single BMP image file or a set of them.

This program differs from others of this sort in two respects:

1. There is no limit on the size of the data file to be hidden because Hermetic Stego can hide a data file, not just in a single BMP image file, but in a set of them -- as many images as needed to contain the data file.

2. The bits of the data are inserted into the bytes of the image files randomly and in such a way as to defeat the use of statistical tests to reveal the presence of a hidden message.

3. The program can be used with a user-specified stego key or with a default stego key; use of a default stego key allows sending hidden data to another person who does not know what that stego key is.