Encrypting data with the Blowfish algorithm

Many embedded systems depend on obscurity to achieve security. We often design systems to download unsigned or unencrypted firmware upgrades or store unencrypted user data, a practice we justify because it’s invisible to the end user and makes our lives easier. The stealthy practice, however, is no longer kosher. With the help of this public-domain encryption algorithm, we can clean up our act.

Modern embedded systems need data security more than ever before. Our PDAs store personal e-mail and contact lists; GPS receivers and, soon, cell phones keep logs of our movements;[1] and our automobiles record our driving habits.[2] On top of that, users demand products that can be reprogrammed during normal use, enabling them to eliminate bugs and add new features as firmware upgrades become available.

Data security helps keep private data private. Secure data transmissions prevent contact lists and personal e-mail from being read by someone other than the intended recipient, keep firmware upgrades out of devices they don’t belong in, and verify that the sender of a piece of information is who he says he is. The sensibility of data security is even mandated by law in certain applications: in the U.S. electronic devices cannot exchange personal medical data without encrypting it first, and electronic engine controllers must not permit tampering with the data tables used to control engine emissions and performance.
Data security techniques have a reputation for being computationally intensive, mysterious, and fraught with intellectual property concerns. While some of this is true, straightforward public domain techniques that are both robust and lightweight do exist. One such technique, an algorithm called Blowfish, is perfect for use in embedded systems.

Links: http://www.embedded.com/columns/technicalinsights/12800442

The DES Algorithm

In 1972, the National Institute of Standards and Technology (called the National Bureau of Standards at the time) decided that a strong cryptographic algorithm was needed to protect non-classified information. The algorithm was required to be cheap, widely available, and very secure. NIST envisioned something that would be available to the general public and could be used in a wide variety of applications. So they asked for public proposals for such an algorithm. In 1974 IBM submitted the Lucifer algorithm, which appeared to meet most of NIST’s design requirements.

NIST enlisted the help of the National Security Agency to evaluate the security of Lucifer. At the time many people distrusted the NSA due to their extremely secretive activities, so there was initially a certain degree of skepticism regarding the analysis of Lucifer. One of the greatest worries was that the key length, originally 128 bits, was reduced to just 56 bits, weakening it significantly. The NSA was also accused of changing the algorithm to plant a “back door” in it that would allow agents to decrypt any information without having to know the encryption key. But these fears proved unjustified and no such back door has ever been found.

The modified Lucifer algorithm was adopted by NIST as a federal standard on November 23, 1976. Its name was changed to the Data Encryption Standard (DES). The algorithm specification was published in January 1977, and with the official backing of the government it became a very widely employed algorithm in a short amount of time.

Unfortunately, over time various shortcut attacks were found that could significantly reduce the amount of time needed to find a DES key by brute force. And as computers became progressively faster and more powerful, it was recognized that a 56-bit key was simply not large enough for high security applications. As a result of these serious flaws, NIST abandoned their official endorsement of DES in 1997 and began work on a replacement, to be called the Advanced Encryption Standard (AES). Despite the growing concerns about its vulnerability, DES is still widely used by financial services and other industries worldwide to protect sensitive on-line applications.

To highlight the need for stronger security than a 56-bit key can offer, RSA Data Security has been sponsoring a series of DES cracking contests since early 1997. In 1998 the Electronic Frontier Foundation won the RSA DES Challenge II-2 contest by breaking DES in less than 3 days. EFF used a specially developed computer called the DES Cracker, which was developed for under $250,000. The encryption chip that powered the DES Cracker was capable of processing 88 billion keys per second. More recently, in early 1999, Distributed. Net used the DES Cracker and a worldwide network of nearly 100,000 PCs to win the RSA DES Challenge III in a record breaking 22 hours and 15 minutes. The DES Cracker and PCs combined were testing 245 billion keys per second when the correct key was found. In addition, it has been shown that for a cost of one million dollars a dedicated hardware device can be built that can search all possible DES keys in about 3.5 hours. This just serves to illustrate that any organization with moderate resources can break through DES with very little effort these days.

Links: 

http://www.aci.net/Kalliste/des.htm

http://www.tropsoft.com/strongenc/des.htm

Blowfish algorithm

Blowfish, a secret-key block cipher is a Feistel network, iterating a simple encryption function 16 times. The block size is 64 bits, and the key can be any length up to 448 bits. Although there is a complex initialization phase required before any encryption can take place, the actual encryption of data is very efficient on large microprocessors.

The cryptographic community needs to provide the world with a new encryption standard. DES [16], the workhorse encryption algorithm for the past fifteen years, is nearing the end of its useful life. Its 56-bit key size is vulnerable to a brute-force attack [22], and recent advances in differential cryptanalysis [1] and linear cryptanalysis [10] indicate that DES is vulnerable to other attacks as well.

Many of the other unbroken algorithms in the literature–Khufu [11,12], REDOC II [2,23, 20], and IDEA [7,8,9]–are protected by patents. RC2 and RC4, approved for export with a small key size, are proprietary [18]. GOST [6], a Soviet government algorithm, is specified without the S-boxes. The U.S. government is moving towards secret algorithms, such as the Skipjack algorithm in the Clipper and Capstone chips [17].

If the world is to have a secure, unpatented, and freely- available encryption algorithm by the turn of the century, we need to develop several candidate encryption algorithms now. These algorithms can then be subjected to years of public scrutiny and cryptanalysis. Then, the hope is that one or more candidate algorithms will survive this process, and can eventually become a new standard.

This paper discusses the requirements for a standard encryption algorithm. While it may not be possible to satisfy all requirements with a single algorithm, it may be possible to satisfy them with a family of algorithms based on the same cryptographic principles.

Links: 

http://www.finecrypt.net/blowfish.html

http://www.schneier.com/blowfish.html