According to Wikipedia a cipher is an algorithm for performing an encryption and decryption - a series of well-defined steps. In other words, ciphers can hide or disclose the content of any message. A basic example is the encryption used by Roman Emperor Gaius Julius Caesar in which every letter of the alphabet is exchanged for another e.g. letters can jump by two places. In this way an "A" becomes "C" and a "B" becomes "D". This is a so called substitution cipher and its principles are still valid today. One of the most well known Caesar ciphers is ROT-13, in which each letter is shifted by 13 steps in the alphabet.

 

Cryptography has greatly evolved since Roman times. Since then the use of polyalphabetic (Vigenère) and more complex computational ciphers has become widespread. Recent developments in information technology and communications necessitate even more sophisticated yet also smaller algorithms that encrypt and authenticate. Three of the best known and most secure ciphers are DES, AES and RSA. Each represents a major breakthrough in cryptography. Take AES for example which was developed under the extreme scrutiny of a public competition facilitated by the National Institute of Standards and Technology (NIST). As a result the AES cipher is extremely secure and also very performant. In traditional IT systems comprised of laptops, desktops and even smart phones, the AES cipher is a fantastic choice for security.

 

When it comes to small, resource-constrained devices however, AES does not perform well.  For instance one of the most power efficient hardware implementations of AES [1] published in literature requires 160 clock cycles (a single computational step) to compute 128-bits of ciphertext.  HB-2 [2] is five times faster requiring only 32 clocks while at the same time consuming only 54% of the power.  The combination of higher performance and lower power has a significant impact on minimizing total energy and therefore increasing battery life.  
 
Moreover, when you consider that most security applications almost always require an authentication component then the savings in total energy used is enhanced even further since HB-2 both encrypts and authenticates in a single pass.  For instance when compared to AES using EAX’ mode (used in ANSI C12.22), HB-2 is roughly ten times faster and consumes between 5 to 10% of the total energy depending on the size of the message.
 
Likewise when comparing Passerine (encryption only) to RSA or ECC we find that on platforms such as the MSP430, Passerine can encrypt eight times faster and requires only one tenth of the codespace.
 
1.   Panu Hamalainen, Timo Alho,Marko Hannikainen, Timo D. Hamalainen, Design and Implementation of Low-Area and Low-Power AES Encryption Hardware Core, Ninth Euromicro Conference on Digital System Design: Architectures, Methods and Tools, IEEE Computer Society, 2006.
 
2.   Daniel Engels, Markku-Juhani O. Saarinen and Eric M. Smith. “The Hummingbird-2 Lightweight Authenticated Encryption Algorithm.” RFIDSec 2011, 7th Annual Workshop on RFID Security and Privacy, Amherst, MA, USA, 26-28 June 2011.