ISSN 2277 – 3916 CVR Journal of Science and Technology, Volume 13, December 2017

SoC Implementation of AES 128 bit Algorithm for

IEEE 802.16e Mobile WiMax Standards
T. Subha Sri Lakshmi
Asst. Professor, CVR College of Engineering/ECE Department, Hyderabad, India
Email: rupashubha@gmail.com

Abstract: Wireless Technology plays a very vital role in data

transmission process. The most widely used wireless technology II. WI-MAX LAYER SECURITY
standard is IEEE 802.16. Especially the basic standards like
Zig-be, Li-Fi, Bluetooth and Wi-Max be the most widely used The link between upper layers and MAC layers used in
for connecting point to multipoint networks wirelessly in a Wi-MAX [1, 8] standard is shown in Figure 1. The security
secured environment. Security is the main issue of any issues are handled in these layers. Being the core part of
transmission system in today's world. Many security IEEE 802.16e, MAC-CPS defines all the processes required
algorithms were proposed for the MAC layer in Wi-Max but
for the proper transmission such as bandwidth requirements,
most commonly used is AES (Advanced Encryption Standard)
algorithm. In this paper 128-bit AES algorithm is implemented connection establishment and management. The connection
in CTR mode. CTR mode is preferred compared to other between the MAC CPS and convergence sub layer (CS) is
modes because it avoids data dependency both in encryption established by MAC service access point (MAC SAP). SAP
and decryption process. All the Blocks were designed using also does other functions like carrying out the
Verilog HDL, simulated using ncvlog simulator, synthesized in communication process, connection and transportation of
cadence- RTL Complier and finally implemented in Soc data over the channel. Encryption and Decryption process
Encounter using GPDK 45nm technology libraries. are performed by privacy sub layer by receiving the data
from higher layers. Processes like authentication and secure
key exchange between base station and subscriber station
Index Terms: AES Encryption/Decryption, Galois field, CTR
mode, RTL Compiler, SoC Encounter. are also performed by security sub layer [3, 5].
Encapsulation and privacy key management are two set of
I. INTRODUCTION protocols required for the smooth condition of the processes
performed by security sub layer.
Security is the main issue both in wireless and wired
communication. Nowadays wireless communication is
growing vast. Broadband Wireless Access (BWA) has been
serving enterprises and operators for years, to the great
satisfaction of its users. However, the new IP-based standard
developed by the IEEE 802.16 is likely to accelerate
adoption of the technology. It will expand the scope of
usage i.e., the possibility of operating in licensed and
unlicensed frequency bands and unique performance under
Non-Line-of-Sight (NLOS) conditions. The most important
features of Wi-MAX are Quality of Service (QoS) for real
time video conferencing and orthogonal frequency division
multiplexing in physical layer of Wi-MAX. Design similar
to OSI model, Wi-MAX [2] uses two layers namely,
physical layer and data link layer. MAC layer in Wi-MAX is
nothing but data link layer in OSI model and is connection-
oriented [2]. MAC layer mainly consists of three sub layer
MAC CS, MAC SAP and MAC Common Part Sub Layer
(MAC CPS) [3]. The main requirement of end user being
the security of data and that service provider to view
unauthorized network access. To solve many security issues,
many protocols like wired equipment protocol (WEP), Li-Fi,
Zig-be, Bluetooth and finally AES. WEP was widely used Figure.1. Overview of MAC layer
till 2009 but was broken by brute force attacks. Finally,
Rijndael AES which assures more reliable and data The process of sending the data packets across the fixed
authentication remains to be the main security issues which Broadband Wireless Access (BWA) is done by
were offered by Rijndael AES in counter mode with Cipher encapsulation protocol which also gives conditional access
Block Chaining (CBC- MAC) mode. by the main station. The privacy key management mainly
has two versions: PKM1 and PKM2 used in mutual

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ISSN 2277 – 3916 CVR Journal of Science and Technology, Volume 13, December 2017

authentications. To refresh the key between main station and operations are but each of the above operation takes its
subscriber station is provided by PKM protocol. Traffic inverse form. For both encryption and decryption, key
encryption keys (TEKs) are exchanged to secure subsequent expansion units are used to generate ten different keys for
PKM which is shared secretly. [8] ten rounds in the case of 128 bit. In every round a new key
is generated from the previous key with the help of a key
III. ADVANCED ENCRYPTION STANDARD matrix and the primary key is referred as cipher. In this
paper, AES is designed for 128 and 256 bit keys with 10 and
AES encryption and decryption [4] use same private key 14 rounds of operations respectively [6]. In the first round,
so it is called as symmetric key block cipher algorithm. For Add Round Key operation is solely performed and in the last
instance, if the block size is 128-bit i.e., it contains 128-bit round, all the operations except Mix column Transformation
information. Here, the input for encryption is the plaintext are performed in both encryption and decryption. The
and output is cipher text which is generated by using ciphers complete process AES encryption and decryption is
and for decryption it is vice-versa. In this different sizes of explained briefly in the form of a flow chart as shown in
keys are used depending upon the number of rounds for data Figure.2.
abstractions which are required. The different sizes of keys
used in AES are 128, 192 and 256 keys for 10, 12 and 14
rounds respectively [4]. Unlike DES, the entire block is used A. Sub Byte Transformation
for each round of operations. The most important in Sub Byte Transformation is the S-
Box. In this operation, the input byte is considered to be one
of the elements of Galios field. The S-Box is implemented
by passing the given input through multiplicative inverse
and then affine transform. For performing this
transformation all the S-Box values will be available well
before hand and store in the memory. The 128 bit data is
presented in 4*4 matrixes in byte format where in the
mappings to S-Box replaces the original data byte [6, 7]. The
mappings to S-Box are as shown in Figure 3(a).

Figure.3 (a). Mapping to S Box

B. Shift Row Transformation

As its name suggests, the shift row transformation is done
Figure.2. AES Encryption & Decryption Process
on 4*4 matrix row by row. In encryption the shift is towards
left and the change in position of bytes depends on the row
Rijndael AES algorithm [9] consists of four operations
number. Elements in 0th row will not be shifted but in 1st ,
namely Sub Byte Transformation, Shift Row
2nd ,3rd rows, the elements are shifted by 1,2 and 3 times
Transformation, Mix Column Transformation and Add
respectively. The shift row operation in encryption
Round Key in encryption. In decryption, the same

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ISSN 2277 – 3916 CVR Journal of Science and Technology, Volume 13, December 2017

performed as shown in Figure. 3(b).For decryption the shift E. Key Expansion

takes place towards right [6]. This unit takes a 128 bit cipher key, and perform a key
expansion routine and generates a key schedule for every
round. This unit contains Subword, Rotword and Rcon (i)
where i represents round number. In every round Rcon (i)
value is assigned and processed. In Subword operation,
SubByte Transformation is applied to the word in that
column. The function Rotword rotates the elements in the
column by one shift from bottom to top. Then the byte is
XORed with Rcon (i) to produce the corresponding column
for the next round.
Figure.3 (b). Shift Row Transformation Process
IV. AES MODES OF OPERATION
C. Mix Column Transformation
Mix Column Transformation operation is one of the most AES block cipher can be implemented in different modes
of operation based on several implementation issues.
power consuming operation in which the multiplication is
Electronic Code Book (ECB), Cipher Feedback (CFB),
carried out by galios field by inter byte mixing. Here, a
Output Feedback (OFB), and counter (CTR) are the
constant 4*4 matrix is used for forward operation and
different types of modes in which AES operates for security
another for reverse operation as shown in Figure.3(c). [6,7]
purposes. In this paper, especially AES algorithm is
implemented in CTR mode [9]. Data dependency of Cipher
Block Chaining mode is avoided in the counter mode with
the value of counter increasing by one in encryption and the
same counter sequences are maintained in decryption
process on the receiver side.

A. AES in CTR Mode

Prior to the encryption of plaintext, an arbitrary block
called nonce and counter is encrypted, and then the result is
XORed with plaintext to create cipher text. Due to the
involvement of counter in encryption, the cipher block is not
the same even if we have same plaintext. Due to non-linear
concept of S-Box this mode avoids the attackers from
Figure.3(b). Mix Column Transformation Process predicting the patterns of repetition in cipher text. Further,
this mode is more suitable for parallel encryption of various
D. Add Round Key
blocks. All these advantages make AES [4, 9] CTR mode be
In this operation, the Mix Column is XORed with the the best choice for AES implementation. The AES CTR
cipher key that is updated in each round using key expansion model is same as shown in Figure.3 (a).
procedure to produce another 4*4 matrix and the output is
given to next round [6] as shown in Figure. 3(d). V. IMPLEMENTATION & RESULTS

All the blocks are implemented using ASIC Cadence SoC

Encounter [10] Tool with 45nm technology libraries.
Figure.4 shows RTL Schematic of AES top module (which
includes both encryption and decryption). Figure.5 shows
RTL schematic of core structure of AES. Figure.6 shows
RTL schematic of Encipher block, Figure.7 shows RTL
schematic Decipher block. The timing of AES module with
positive slack is 650ns. Figure. 8 shows the net power usage
of AES. Table I and Table II, give the pre & post clock tree
synthesis report in terms of nano seconds when routing is
performed before special route and after nano route process.
Finally, Figure.9 shows the IC chip Fabrication Layout
structure which is named as GDS II file of AES top module.

Figure.3 (d). XORed Operation Process Structure

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ISSN 2277 – 3916 CVR Journal of Science and Technology, Volume 13, December 2017

Language Used - Verilog HDL

Simulator Tool - Ncvlog
Synthesis Tool - RTL Compiler
Implementation (Back-End Process) - SoC Encounter
Power Analysis n terms of nano watts
a) Internal Power - 0.650 (50%)
b) Switching Power - 0.62 (48%)
c) Leakage Power - 0.0006 (0.5%)

Figure.7 RTL Schematic of AES Decipher Block

Figure. 4 RTL Schematic of AES Top Module

Figure. 8. Net Power Usage

Figure. 5 RTL Schematic of AES Core Structure

TABLE I
PRE CLOCK TREE SYSTHESIS REPORT

Figure. 6 RTL Schematic of AES Encipher Block

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ISSN 2277 – 3916 CVR Journal of Science and Technology, Volume 13, December 2017

TABLE II [6] Willam Stallings (2008) Cryptography and Network Security.

POST CLOCK TREE SYNTHESIS REPORT 5th addition Prelitce Hall, Pearson Education, USA.
[7] Tshering, F. and Sardana, A. (2011) A review of privacy and
Key Management Protocol in IEEE 802.16e. International
Journal of Computer Applications,20,25-31.
[8] Mohamed, M.A., Zaki, F.W and El-Mohandes,A.M (2012)
Novel fast Encryption Algorithm for Multimedia
Transmission over Mobile WiMax Networks. International
Journal of Computer Science,9,60
[9] Litochevski, M. and Dongjum, L. (2012) High Throughout
and Low Area AES: Core Specifications, Opencores,1-9.
[10] Prof.Micea Stan, Cadence SoC Encounter, University of
Virginia.

Figure. 9. GDS II of AES Top Module

VI. CONCLUSIONS
All the blocks are verified by ncvlog simulator and
synthesis by using RTL complier and finally implemented in
SoC Encounter and IC chip layout is obtained i.e., GDS II
file. The top module consist of encipher and decipher blocks
which is further designed by using inverse S-Box. The main
advantage of AES algorithm in counter modes is, it
consumes very less power as shown in figure 8 and as well
as area occupancy on IC is also very less. These features
play a prominent role for portable devices and have
advanced improvements for Mobile Wi-MAX devices.

REFERENCES
[1] Dadhich,R.,Narang,G. and Yadav, D.M (2012) Analysis and
Literature Review of IEEE 802.16e (Mobile Wi-MAX)
security. International Journal of Engineering and Advanced
Technology, 1,167-173.
[2] Khan, A.S., Fisal, N., Maqbool, W., Ullah, R. and Sardar, H.
(2014) Secure Authentication and key Management Protocols
for Mobile Multichip WiMAX Networks. Indian Journal of
Science and Techology,7,282-295.
[3] Hasan, J. (2006) Security issues of IEEE 802.16 (WiMAX).4th
Australian Information Security Management Confernece,
Perth, 5 December 2006.
[4] FIPPUB197 (2001) Advanced Encryption Standard (AES).
November 2001.
[5] Rajeeth, K.D., Alukaidey, T., Salman. K.and Alzaabi,
M.(2013) Security Algorithm for WiMAX. International
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