RUBBERHOSE review by Steven Baum

Rubberhose is a deniable cryptography package that lets someone not wanting to disclose plaintext data corresponding to their encrypted data show that there is more than one interpretation of the latter.

Rubberhose works by initially writing random characters to an entire hard drive or other dynamic storage device. This random noise is indistinguishable from the encrypted data to be stored on that disk. If you have a 1 GB drive and want to have two Rubberhose encrypted portions of 400 MB and 200 MB, it assumes that each aspect (as the encrypted partitions are called) will be 1 GB and fill the entire drive. It will keep doing this until the drive is really filled to capacity with encrypted material. It breaks up the pieces of each aspect into small pieces and scatters them across the entire 1 GB drive in a random manner, with each aspect looking as if it is actually 1 GB in size upon decryption.

Each aspect has its own passphrase that must be separately decrypted, and if a hard drive is seized neither mathematical analysis nor physical disk testing can reveal how many aspects actually exist. Internal maps are used to locate where the data is stored amongst the random characters, with each aspect having its own map which can only be decrypted via its specific passphrase. As such, a Rubberhose disk only be written to after all the passphrases have been entered. Everything is works on a "need to know" basis, i.e. each aspect knows nothing about the others other than when to avoid writing over the top of another.

Other features of Rubberhose include:

• a choice of cryptographic algorithms including DES, 3DES, IDEA, RC5, Blowfish, Twofish and CAST;
• compatibility with several filesystems including UFS, ext2fs, FAT and FAT32;
• time-based passphrases, e.g. configuring it to demand re-entry of a passphrase after a given amount of time or to lock out users after a specified amount of idle time;
• anti-passphrase-cracking features, e.g. an internally generated passphrase is generated upon the creation of each new aspect that is encrypted with the user passphrase for that aspect;
• a design ensuring that if one block of data in an aspect is decrypted, then it cannot be used to decrypt the remaining blocks;
• frequent block-swapping to confound disk surface analysis based on the intensity of block use and contiguous block prediction; and
• "whitening code," i.e. code for the prevention of plaintext attacks that perturbs the encryption process in a non-predictable way such that some bits in an encrypted block are flipped and some aren't.

Rubberhose was originally conceived by crypto-programmer Julian Assange as a tool for human rights workers who needed to protect sensitive data in the field, particularly lists of activists and details of incidents of abuse. Repressive regimes in places like East Timor, Russia, Kosovo, Guatemala, Iraq, Sudan and The Congo conduct human rights abuses regularly. Our team has met with human rights groups and heard first-hand accounts of such abuses. Human rights workers carry vital data on laptops through the most dangerous situations, sometimes being stopped by military patrols who would have no hesitation in torturing a suspect until he or she revealed a passphrase to unlock the data. We want to help these sorts of campaigners, particularly the brave people in the field who risk so much to smuggle data about the abuses out to the rest of the world.