A Cryptographic Hardware Revolution in Communication Systems using Verilog HDL

Full Paper
Int. J. on Recent Trends in Engineering and Technology, Vol. 9, No. 1, July 2013

A Cryptographic Hardware Revolution in
Communication Systems using Verilog HDL
1

Jasyanth Koppula and 2Bala Sindhuri Kandula

1

M.Tech student, Department of Electronics and Communication Engineering, SRKR Engineering College, Bhimavaram,
Andhra Pradesh, India
jasyanth.koppula@ yahoo.com
2
Asst Professor, SRKR Engineering College, Department of Electronics and Communication Engineering, Bhimavaram,
Andhra Pradesh, India
k.b.sindhuri@gmail.com
required multiplications are performed using a single resource
shared multiplier with the commensurate area saving.
The ASIP achieves an average encipher-decipher
throughput of 3.1Mbps and utilizes less than the one third of
the resources of smallest Xilinx Virtex VI (XC6VCX240T).
The results presented are for Xilinx FPGAs, however, the
optimizations made are equally applicable to other vendor’s
FPGAs. The comparison between FPGA designs [3] which
incorporate ROMs and those which do not is sometimes problematic. Here, this is solved by converting the amount of
block memory used into an equivalent number of slices. This
yields a single area figure for any design. The throughput–
area ratio is frequently used as the academic measurement of
design efficiency, however, there are economic and engineering savings to be made by striving towards the lowest possible area design which meets the overall system requirements. The designs in this paper are aimed at challenging the
lowest area end of the design space while still providing a
usable throughput.

Abstract— Advanced Encryption Standard (AES), is an
advancement of Federal Information Processing Standard
(FIPS) which is an initiated Process Standard of NIST. The
AES specifies the Rijndael algorithm, in which a symmetric
block cipher that processes fixed 128 bit data blocks using
cipher keys with different lengths of 128, 192 and 256 bits.
The earliest Rijndael algorithm had the advantage of
combining both data block sizes of 128, 192 and 256 bits with
any key lengths. AES can be programmed in pure hardware
Verilog HDL, Which includes Multiplexer to enhance more
secure to Cipher text. The results indicate that the hardware
implementation proposed in this project is Decrementing
Utilization of resource and power consumption of 113 mW
than other implementation. Using FPGA lead to reliability on
source modulations. This project presents the AES algorithm
with regard to FPGA and Verilog HDL. The software used for
Simulation is ModelSim-Altera 6.3g_p1 (Quartus II 8.1).
Synthesis and implementation of the code is carried out on
Xilinx ISE 13.4 (XC6VCX240T) device is used for hardware
evaluation.
Index Terms- FIPS, FPGA, Modelsim software, NIST, Rijndael
algorithm, Verilog HDL, Xilinx ISE.

II. DESCRIPTION OF AES ALGORITHM
The algorithm is composition of three main parts Cipher
Text , Inverse Cipher Text, and Key Expansion. The Cipher
converts normal text to an unintelligible form called cipher
text while Inverse Cipher converts data back into its original
normal text form called plaintext. The Key Expansion
generates a Key Schedule that is used in Cipher and Inverse
Cipher procedure. The Cipher and Inverse Cipher are
composed of specific number of rounds shown below (Table
1). For the AES algorithm design [4], the number of rounds to
be performed during the execution of the algorithm is
dependent on the key length.
The sequence in which the operation is carried out is as
follows:
Round 1:

I. INTRODUCTION
In the recent years, Using FPGA in production versions
of electronic systems increased. Advanced Encryption Standard (AES) FPGA [5] designs typically unroll the loops within
the AES design followed by deep pipelining of a 128 Bit data
path to achieve throughputs of the order of tens of gigabits
per sec based on The National Institute of Standards and
Technology (NIST) Standards. These designs have utility in
applications such as hardware accelerator cards for e-Commercial servers & secure trunk communication.
This design for AES on FPGAs design [1]-[2], which is an
8 bit Application Specific Instruction Processor (ASIP) which
supports key expansion (can be programmed for 128 bits)
encipher and decipher. This design less than 40% of the
resources of the smallest available Xilinx Virtex VI. This can
be used in applications, which had low power and low Area
as priorities design [2].
An ASIP capable of performing AES encipher and
decipher operations using a truly 8-bit data path. The design
utilizes a novel version of the Sub- Bytes operation using
existing composite field arithmetic[9], However, the three
© 2013 ACEEE
DOI: 01.IJRTET.9.1.11

A. Add Round key.
Following Rounds:
A. Sub Bytes.
B. Shift Rows.
C. Mix Column.
D. Multiplexer.
E. Add Round Key.
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alternative designs [8] for decipherment. In this design, the
one where the Round-Keys are the same as encipher was
selected. These are applied in reverse order for decipherment.

TABLE I: N UMBER OF ROUNDS IN AES ALGORITHM
Algorithm
AES-128-bits
key

Block Size
(Nb Words)
4

Key Length
(Nk Words)
4

Number
of
Rounds (Nr)
10

A. Sub Bytes:
AES-192-bits
key

4

6

12

AES-256-bits
key

4

8

14

In the sub bytes stage the data in the plain text form is
substituted by some predefined values from a substitution
box which is an invertible form [9].
B. Shift Rows:
In shift rows operation the rows in the 4×4 matrix is shifted
to left r bits and r varies with the rows of the matrix(r=0 for
row1, r =1 for row2, r =2 for row3, r =3 for row 4). This process
is illustrated in figure 2.

Final Round:
A. Sub Bytes.
B. Shift Row.
C. Add Round Key

Fig 2: Shift Rows

C. Mix Columns
MixColumns is calculated using the below formula. Here
a0, a1, a2, a3 is calculated using the polynomials as below
a(x) = {2}x3 +{3}x2 + {1}x + 1

The MixColumns transformation operates on the step
column by column, generating each column as a four term
polynomial as in Figure 3. The Columns are assumed as
polynomials over GF (28) and multiplied modulo x4 + 1 with a
fixed polynomial a(x) which is got from the above formula.
This can also written as a matrix multiplication
s’(x) = a(x) c(x)
(2)

Fig 1: Basic Concept of the Algorithm

This is shown in figure 1. The AES algorithm can be
implemented in both hardware and software. The software
implementation of AES algorithm is a slow process when
compared with hardware process.
III. AES ENCRYPTION PROCESS
Briefly, this block cipher can perform encipher and decipher operations using the repeated operation of a Substitute
Permute Network (SPN) on 128 bits of data.
Each time the SPN is used it is supplied with a different
RoundKey. These are generated by a function known as
KeyExpansion. Three different key lengths were specified,
128, 192 and 256 bits. Which in turn require 10, 12 and 14
rounds of substitution and permutation. The first and final
rounds differ from the middle rounds and the overall process
is summarized in Fig. 1. The AES specification provides two
© 2013 ACEEE

(1)

Fig 3: Mix Column

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The first Nk words of the expanded key are filled with the
cipher key. Every word w[i] is equal to the XOR of previous
word w[i-1] and the word Nk positions earlier w[i-Nk]. For the
words in positions that are a multiple of Nk, a transformation
is applied to w[i-1] prior to the XOR and followed by an XOR
with a round constant Rcon[i]. This transformation contains
a cyclic shift of the bytes in a word rotword() and byte
substitution subword(). But in key expansion of 256-bit cipher
if Nk=8 and i-4 is a multiple of Nk then subword() function is
applied to w[i-1] prior to the XOR.

D. Multiplexer 2:1:

Fig 4: Single round of AES algorithm using MUX

In this Algorithm Multiplexer is used between Shift Row
and Mix Columns as in Figure 4. This is design [10] used to
enhanced the security of the cipher text and also to ensure
the quick processing of the cipher text.
E. Add Round Key:
In the add round key step the 128 bit data is XORed with
the sub key of the current round using the key expansion
operation. The add round key is used in two different places
one during the start that is when round r = 0 and then during
the other rounds that is when 1 d• round d• Nr, where Nr is
the maximum number of rounds. The formula to perform the
add round key is
S’(x) = S(x) R(x)
S’(x) – state after adding round key
S(x) – state before adding round key
R(x) – round key

Fig 5: AES Encryption Process

F. Key Expansion:

IV. AES DECRYPTION PROCESS

The key expansion has three steps:
a) Byte Substitution subword ( )
b) Rotation rotword ( )
c) XOR with RCON (round constant)
The input to key schedule is the cipher key K. Key
expansion generates a total of Nb (Nr + 1) words as shown in
Figure 5. The algorithm requires an initial set of Nb words
and each of the Nr rounds requires Nb words of key data. The
obtained key schedule consists of a linear array of 4-byte
words, denoted [wi], with i in the range 0 d” i < Nb (Nr + 1).
The subword( ) function takes a four byte input and applies
the byte substitution operation and produces an output word.
The rotword ( ) takes a word [a0, a1, a2, a3] as input and
performs a cyclic permutation to produce [a1, a2, a3, a0] as
output word. The round constant word array rcon [i] is
calculated using the below formula in finite field.
rcon[i]= x(254+i) mod x8+ x4+ x3+x+1
(3)
© 2013 ACEEE

The decryption of the data which was encrypted using
the AES is done by inverting all the encryption operations
with the same key with which it is encrypted since the AES is
a symmetric encryption standard. In the design [4], decryption
process the sequence of the transformations differs from that
of the encryption but the key expansion for encryption and
decryption are the same. The several properties of the AES
algorithm [7] allow for an equivalent decryption with the
same sequence of transformations as that in encryption.
The operations of the decryption process are listed below
A. Inverse Sub Bytes.
B. Inverse Shift Rows.
C. Add Round Key.
D. Inverse mix columns.

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A. Inverse Sub Bytes:
This operation is similarly as it is in the encryption process
but the only difference is the inverse of the substitution box
is used here since the substitution box which we used in the
encryption is invertible.
B. Inverse Shift Rows:
The inverse shift rows operation is an inverse process of
the shift row operation in the encryption process by right
shifting the elements in the rows.
Fig 7: Circuit diagram for AES algorithm

C. Add Round Key:
The add round key process is as same as that of the one
in the encryption process.

TABLE II : AES-128 IMPLEMENTATION RESULTS
DEVICE

FREQUE
NCY(MH
Z)

ARE
A

THROUGHP
UT(MBPS)

AES-128

VIRTEX 5

174.166

2,499

2229

AES-128

VIRTEX 6

200.087

2,715

4998

AES-128

VIRTEX 4

75.850

6,076

4677

AES-128

SPARTAN 6

249.236

5,067

4012

DESIGN

D. Inverse Mix Columns:
In inverse mix column operation is the same operation in
the mix column is done but with the different matrix as in
Figure 6.

VI. TESTING AND VERIFICATION
To ensure the proposed design gives better results in
terms of Utilization and Power Consumption the design is
implemented Xilinx Virtex VI (XC6VCX240T) and FPGA
device used for downloading. The device Comparison table
of algorithm as shown in Table III i.e. AES-128 in same
hardware is shown.
TABLE III: COMPARISON WITH OTHER DESIGNS
Design
AES 128
[1],[6]
[2]

Area
(CLBs)
2715
6701
3328

Throughput/
area
1.840
0.173
0.106

The power consumption of the device for the algorithm
i.e. AES-128 is 113 mW on the same hardware.
Input is taken as text data which is also known as plaintext.
Here the plaintext is encrypted with the help of key. Finally
the encrypted data obtained in unknown form as shown in
Figure 8.
Key: 000102030405060708090a0b0c0d0e0f
Input: 0a940bb5416ef045f1c39458c653ea5a
Output: XZXZ2a502ed505bbc117c70e5163194f
The Encrypted data is given as the input to the decryption
block which will gives the original Plaintext as the output.
The output obtained by using Modelsim 6.1 is shown in Figure
9.
Key: 000102030405060708090a0b0c0d0e0f
Input: XZXZ2a502ed505bbc117c70e5163194f
Output: 0a940bb5416ef045f1c39458c653ea5a

Fig 6: AES Decryption Process

V. IMPLEMENTATION
The AES algorithm is implemented using Verilog HDL
coding in Xilinx ISE 8.1. First, the algorithm is Simulated using ModelSim by encrypting and circuit Diagram is obtained
as shown in Figure 7 and decrypting a single 128 bit block
and Synthesizing and implementation of the code is carried
out on Xilinx ISE 13.4 device. Then the key is expanded to
use for 192, 256 bit blocks. The Power Consumption is 63%
and Utilization is more than the previous projects [2], [6],
which is double than other implementations. The implementation output is shown in Table II
© 2013 ACEEE

Throughput
(MBPS)
4998
1163
353

Throughput Area is 4998 MBPS
Power Consumption is 113mW
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Synthesizable Verilog code is developed for the
implementation of both encryption and decryption process
using Xilinx Family. Each program is tested with some of the
sample vectors provided by NIST. The combination of
security, and low power consumption implementation makes
it a very good choice for wireless communication systems.
APPENDIX A: TERMS AND DEFINITIONS
The following definitions are used throughout the
algorithm:
AES: Advanced Encryption Standard Affine a
transformation consisting of multiplication by a matrix
followed Transformation by the addition of a vector
Array: An enumerated collection of identical entities (e.g.,
an array of bytes).
Bit: A binary digit having a value of 0 or 1.
Block: Sequence of binary bits that comprise the input,
output, State, and Round Key. The length of a sequence is
the number of bits it contains. Blocks are also interpreted as
arrays of bytes.
Byte: A group of eight bits that is treated either as a single
entity or as an array of 8 individual bits.
Cipher: Series of transformations that converts plaintext
to ciphertext using the Cipher Key. Cipher Key: Secret,
cryptographic key that is used by the Key Expansion routine
to generate a set of Round Keys; can be pictured as a
rectangular array of bytes, having four rows and Nk columns.
Ciphertext: Data output from the Cipher or input to the
Inverse Cipher.
Inverse Cipher: Series of transformations that converts
ciphertext to plaintext using the Cipher Key.
Key Expansion: Routine used to generate a series of Round
Keys from the Cipher Key.
Plaintext: Data input to the Cipher or output from the
Inverse Cipher.
Rijndael: Cryptographic algorithm specified in this
Advanced Encryption Standard (AES).
Round Key: Round keys are values derived from the Cipher
Key using the Key Expansion routine; they are applied to the
State in the Cipher and inverse Cipher.
State: Intermediate Cipher result that can be pictured as a
rectangular array of bytes, having four rows and Nb columns.
S-box: Non-linear substitution table used in several byte
substitution transformations and in the Key Expansion
routine to perform a one for-one substitution of a byte value.
Word: A group of 32 bits that is treated either as a single
entity or as an Array of 4 bytes.

Fig 8: Wave forms of Encryption using Xilinx

Fig 9: Output using Modelsim 6.1

VII. CONCLUSION
The Advanced Encryption Standard algorithm is an
iterative private key symmetric block cipher that can process
data blocks of 128 bits through the use of cipher keys with
lengths of 128, 192, and 256 bits. Here Focus is on
implementing AES algorithm using the reconfigurable
hardware technology based on Field Programmable Gate
Arrays (FPGA) in Verilog HDL. The architecture of an iterative
AES and Deep pipeline architecture of algorithm is presented.
The algorithm can accept data and keys of 128 bits. It can
achieve a maximum throughput of 4998 MBPS. The achieved
Power consumption is about four times lesser than other
methods [1], [2], [6]. reported A less power Consumption of
113mW is achieved using this architecture. Optimized and
© 2013 ACEEE

APPENDIX B: ALGORITHM PARAMETERS, SYMBOLS, AND
FUNCTIONS
The following algorithm parameters, symbols, and
functions are used throughout this standard:
Add RoundKey () : Transformation in the Cipher and
Inverse Cipher in which a Round Key is added to the State
using an XOR operation. The length of a Round
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Key equals the size of the State (i.e. for Nb =4, the Round
Key length equals 128 bits/16 bytes).
InvMix Columns (): Transformation in the Inverse Cipher
that is the inverse of MixColumns().
InvShift Rows (): Transformation in the Inverse Cipher
that is the inverse of ShiftRows().
InvSub Bytes (): Transformation in the Inverse Cipher that
is the inverse of SubBytes().
K: Cipher Key.
Mix Columns (): Transformation in the Cipher that takes
all of the columns of the State and mixes their data
(independently of one another) to Produce new columns.
Nb: Number of columns (32-bit words) comprising the State.
For this standard, Nb = 4.
Nk: Number of 32-bit words comprising the Cipher Key. For
this standard, Nk = 4, 6, or 8.
Nr: Number of rounds, which is a function of Nk and
Nb(which is fixed). For this standard, Nr = 10, 12, or 14.
Rcon[]: The round constant word array.
RotWord (): Function used in the Key Expansion routine
that takes a four-byte word and performs a cyclic permutation.
ShiftRows (): Transformation in the Cipher that processes
the State by cyclically shifting the last three rows of the State
by different offsets.
SubBytes (): Transformation in the Cipher that processes
the State using a Nonlinear byte substitution table (S-box)
that operates on each of the State bytes independently.
SubWord (): Function used in the Key Expansion routine
that takes a four-byte input word and applies an S-box to
each of the four bytes to produce an output word. XOR
Exclusive-OR operation.

© 2013 ACEEE

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A Cryptographic Hardware Revolution in Communication Systems using Verilog HDL

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