The advancement in technology leads to the reduction in size and power consumed by the devices used to perform real world operations including of which are like sensor networks, RFID Tags, controllers, smart cards and deployment of embedded system etc. The functionality of all these systems consists of storage, manipulation and transmission of some data and along with this the major concerning factor is security which is achieved by cryptography. The changes in the basic parameters of size and power requirement make large difference in the basic security and operational functions of these resource constrained devices because it is difficult to apply the conventional security methods and techniques used in other devices.
Lightweight cryptography is the specific field of cryptography providing security principles and algorithms for resource constrained devices usually small sized and those which consumes less power. Today almost every smart device consists of some microcontrollers, gates and basic electronic components and all these defines the functionality ,implementation of security procedures as in case of microcontrollers they are available in wide ranges starting from 4 bit up to 32 bit, but for small scale and low cost applications 4 bit is generally used due to it’s small size instruction sets and if convention cryptographic algorithms are used in these controllers it is difficult to implement them due to large processing times and higher energy used . This report gives the overview about lightweight cryptography with the potential security threats and the vulnerabilities in the resource constrained systems with the profiles which includes basic design concepts like physical characteristics, performance characteristics, latency and some security characteristics This report also reviews working mechanism with the performance of popular lightweight algorithms which are PRESENT and elliptic curve.
POTENTIAL SECURITY THREATS IN SYSTEM LOW POWER
1. Confidentiality threats
Confidentiality is very important aspect in securing low power devices information and the confidentiality threats are the threats consisting of obtaining sensitive information without the trusted party consent and attacker might change or view the information taking instance of home monitoring systems, breaching the confidentiality in the internet based system for monitoring home may lead to leakage of sensitive and personal data like knowledge of place occupied and timings when nobody is at home .Loss of such confidential details leads to unauthorized entries in the secure systems.
2. Authentication threats
RFID tags are the smallest live example for low power devices which uses inductions or fields and to secure these devices lightweight cryptography comes in effect. Attacks associated with RFID tags can be physical and channel threats like disabling, modifying content, cloning, erasing memory of tag etc. Threats which uses channels as medium to find the loophole in system are RFID channel threats and may include eavesdropping, snooping or privacy leaks.
3. Vulnerabilities in systems with low power devices
Resource constrained system in either power, computational speed or memory terms is itself a vulnerability, as the most of the controllers used at small scale projects and applications are 4 bit or 8 bit so it is very difficult to implement complex security algorithms.
WORKING MECHANSISM OF LIGHTWEIGHT CRYPTOGRAPHY
The lightweight cryptographic primitives consist of block ciphers, stream ciphers and hash functions provide advantages and better performance as compared to implementing conventional algorithms as lightweight cryptography is meant for specific range of applications. Lightweight cryptography is not low level security approach always but the concept is to use advancements for trade off and balance between resources, battery constraint and performance.
Lightweight Block Ciphers
There are various lightweight block ciphers for better performance and merits, some of which are built by modifying and making the conventional block ciphers simple for better efficiency. PRESENT is such of first lightweight block cipher design made for restricted availability of resources.
The merits of lightweight block cipher in comparison with conventional block ciphers are:
1. Small key size
2. Simple key schedule
3. Small block size
Lightweight hash functions
Due to large internal states and requirement of high power and energy consumption, conventional hash functions cannot be used for resource constrained devices and environment. The examples of lightweight hash functions are PHOTON, SPONGENT.
The differences between conventional hash functions and lightweight hash functions are as follow:
1. Smaller message size
The majority of lightweight hash functions input sizes of message are much smaller which can be less than or equal to 256 bits.
2. Smaller internal and output stages
For the collision resistance of hash functions, the outputs with large sizes are must and for the applications for which these collision resistances are not so important smaller internal and output sizes can be used.
The concept of lightweight cryptography has direct impact on cost, size, power used and speed of the system because high level of security is achieved in traditional cryptography without considering these factors. In designing cryptographic algorithm the balance should be achieved between performance and the resources which are expected for certain level of security. Performance can be defined in terms of factors such as latency, power and energy consumption. The resources include implementing hardware which is expressed in terms of gate equivalents, gate areas, logic blocks and in terms of software resources they are categorized under RAM, ROM and registers usage.
Latency is crucial for real time applications like very fast response in situations while driving such as airbag deploy system, anti-braking system steering response in emergency condition. Latency is defined as the time measure between initial request for operation and response for the same request and in encryption terminology it can be explained as time between giving plain text and receiving cipher text after data encryption.
HARDWARE SPECIFIC METRICS
The gate area is basic term to define the measure of hardware resources required and is expressed in terms of m 2 and which depends on the standard cell library and the technique used for the specific application. Area is stated in the terms of logic blocks for FPGA and gate equivalents for
On field programmable gate array, logic blocks consist of multiplexers, flip flops look-up tables which is different for different FPGA depends on FPGA family and on the number of input and output bits in look up tables. Gate equivalent in ASICs is equivalent to the area used by two-input NAND gate and is calculated by dividing the area in m 2 by area of NAND gate. It is different for different technologies and is not easy to compare among them because it is defined for specific technology used for hardware implementation.
SOFTWARE SPECIFIC METRICS
The Focusing metrics in case of software implementation, are RAM consumption, size of implementation code and through put. Throughput can be defined as the rate of producing new outputs and is expressed in terms of bytes per cycle and in comparison to general cryptographic techniques, the lightweight cryptographic algorithms are not meant for high through put. RAM is used in manipulation of data that can be computations at intermediate values whereas ROM is for storing program code including fixed data.
LIGHTWEIGHT CRYPTOGRAPHIC ALGORITHMS
PRESENT is one of the example of ultralight weight block cipher which uses smaller block sizes and potential for small keys like 80 bit generally consists of 31 rounds with block length of 64 bits and uses substitution and permutation network method by supporting two key lengths out of which it can be either 80 bits which is 10 HEX characters or128 bits which is 16 HEX characters and for the low-security applications it is more than adequate security generally in tag based applications.
Each rounds in 31 rounds includes an XOR operation to introduce round key ki where i lies between 1 to 32. The basic function of S box is that it replaces small block with another block of bits and this substitution must be one to one to ensure correct decryption whereas P box scrambles the bits in some defined manner.
figure: top level algorithmic description of PRESENT
source: adapted from research paper PRESENT: An ultra-
lightweight Block cipher
Elliptic curve cryptography was purposed in mid 1980’s which uses sloping curves instead of using large prime numbers as in case of RSA. It is asymmetric cryptographic algorithm which is also referred to as public key cryptography and one of merit of elliptic curve cryptography is the shorter size of key length to provide nearly same level of security as other public key cryptography systems. Elliptic curve cryptography gives high speed implementation using less power and bandwidth which is concerning factor in case of embedded devices or other lightweight applications.
figure: Elliptic curve cryptography
source: adapted from international journal of CS&IT (IJCSIT, vol3, no. 3, june 2011)
CURRENT AND FUTURE TRENDS WITH CHALLENGES
Today the changing demands of the users and industries replaces most of the wired and large scale systems with embedded systems consisting of micro controllers for the communication and informational purposes and all these changes required certain security for the reliable and secure operations. The resultant for securing of embedded systems and networks with tiny computing low power devices is light weight cryptography. Lightweight cryptography can become the important component for IOT as with increasing demand for internet in simple and small devices also for remote purposes. The tiny computing devices are in routinely use in daily routine use like RFID’s tag and also these form an integral part of pervasive communication. The challenges may be varied depending on the application area and the hardware and software specifications.
In future the deployment of hardware optimized block and stream ciphers can be proposed for security of resource constrained devices without compromising it. The basics is always to include less gate equivalents and robust and less cycles instruction codes. There are problems related to chip power and area usage in specific application like RFID tags memory leaks, modications and formatting them. These challenges should be considered while using cryptography in resource restricted devices.
Lightweight cryptography focuses on the security issues of smart networks consists of hardware or software restrictions by providing efficient and adequate security. The conventional algorithms for cryptography are not suitable for the devices with low power and resource constrained systems. There are some challenges also associated with the lightweight cryptography because of some factors like software and hardware restrictions which so there can be modifications or optimizations in system hardware or software to achieve sufficient security. so there can be modifications or optimizations in system hardware or software to achieve sufficient security.
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