Under Lock and Key

Fri, 02/28/2003 - 7:00pm
Under Lock and Key

Protecting sensitive data
Bill Weaver, Ph.D.

During my morning commute, I mused about a thesis on data security. I locked the front door and deadbolt of the house, used my keychain transmitter to unlock the car, started it up with the ignition key, passed through toll booths using my windshield-mounted transponder, swiped my ID card to raise the arm at the faculty parking lot, locked the steering wheel anti-theft device, locked the car and started my walk across campus — still no ideas. Swiped my card into the mail room, spun the combination to open my box, swiped my card into the science building, unlocked my office, and logged into my computer. I still haven't come up with a clever thesis, so I will just say security is really important.

The tried and true method to secure valuables is simply to hide them from view. However, a weak link is created when recording the location for future retrieval. The proverbial "x-marks the spot" treasure map displays detailed instructions on steps to find the valuables — steal the map, you've stolen the treasure. Modern combination locks, metal key/lock systems, and electronic passwords are variations on this theme. The security burden shifts from protecting valuables to protecting keys.

Protecting information is slightly different. By definition, information is that which flows between a transmitter and receiver. Since the transmission medium is often unsecured, information can be made less vulnerable to theft by hiding its meaning using non-standard symbols. It is said that Julius Caesar used such a cipher to encode messages by replacing each letter with one three positions further along in the Latin alphabet. A modern-day version known as rot13 is used by Usenet newsgroups to hide inappropriate language or punch lines. Rot13 is a secret key cipher — both sender and receiver must know the secret to unlock information. Since the same key is used to both encode and decode information, it is also known as symmetric encryption. In 1977, the National Institute of Standards and Technology (NIST) published the Data Encryption Standard (DES) for secret key transmission systems. Based on IBM research, DES uses an algorithm with a 56-bit key to scramble and unscramble each 64-bit block of the transmission. While highly infeasible using late-1970s technology, it is now possible to compute and apply every possible 56-bit key code combination in a reasonable time. Recently, NIST supplanted DES with the Advanced Encryption Standard (AES), which utilizes an algorithm with 128-, 192-, and 256-bit keys. While efficient, the Achilles heal of symmetric encryption is distribution of keys. If keys must be transmitted to the receiver before applied, an extremely secure transmission system must be utilized to keep them secret. However, a system secure enough to transmit keys should be used to transmit the message itself.

This paradox is eliminated using asymmetric or public key encryption, such as the RSA algorithm developed in 1977 by Ronald Rivest, Adi Shamir, and Leonard Adleman and owned by RSA Security. The algorithm generates two different, yet interdependent, keys of up to 2048-bits in length. Either can be used for encryption but they must be used together for decoding. The interdependence is based on factorization of very large prime numbers difficult to derive using current mathematical theorems. The advantage is only the public key needs to be transmitted while the private key remains hidden. In order to receive an encoded message, the intended receiver transmits the public key to the potential transmitter who uses it to encrypt the message. The scrambled message is then transmitted over nominally insecure channels to the receiver who uses the public key in concert with the private key to decode it. RSA algorithm is the basis of Secure Socket Layer (SSL) Internet transmission protocol developed by Netscape. It is also used to meet 21 CFR Part 11 standards governing data security and digital signatures. A transmitter can encrypt a digest or digital fingerprint of the message using a private key and transmit this digital signature along with the message. If the receiver decodes it successfully using the transmitter's public key, then the message is considered authentic. More-over, the it can be used to verify that the document has not changed since signed. As data acquisition systems become more distributed, security will play an increasingly important role.

Bill Weaver, an assistant professor in the Integrated Science, Business and Technology Program at LaSalle Univ., may be reached at


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