Please recommend tools that will encrypt the contents of a single folder on a single NTFS volume in Windows 7.
To be clear, the utility must automatically encrypt any data saved/moved into the specified folder. This is a foremost requirement.
Regarding the encryption cipher, AES (Rijndael), Serpent, Blowfish, or Twofish are preferred. Other ciphers can be considered, but will need to be evaluated.
This software will only need to be used occasionally. Therefore, it is ideal if this software can be run on demand to create an encrypted folder, and then terminated when the encrypted folder is no longer needed. It's fine if all data in the encrypted folder is lost when the application is terminated.
Cost needs to be under 10€, but gratis is preferred.
Open-source software is a big plus, but not required.
Windows 7 compatibility is required. If the tool is also compatible with Linux, that's a big plus, but not required.
The most minimalistic installation is preferred. Portable software is ideal, but given the required functionality, true portable software may not be possible. As such, an application that can be manually installed is preferred over ones that require an installer. That said, applications that require a formal installer will still be considered, and recommendations for them will also be appreciated.
