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Review of Cryptography and SteganographyReview of Cryptography and SteganographyReview of Cryptography and SteganographyReview of Cryptography and Steganography
TechniquesTechniquesTechniquesTechniques
Anika Anand1, Deepak Gupta2
1M.Tech Student, Vaish College of Engineering, Rohtak, Haryana (India)[email protected]
2Associate Professor, Vaish College of Engineering, Rohtak, Haryana (India)
Abstract
Information security is of utmost importance in todays fastdeveloping era. Information or messages are beingexchanged over various types of networks. A large part of
this information is confidential or private which increasesthe demand for a more robust method of data transfer.Steganography and Cryptography are two widely used
techniques that manipulate information in order to cipher or
hide their existence. Steganography is an art and science ofhiding the message in such a way that no one other than theintended recipient knows about the existence of message.
Steganography can be applied on many objects like audio,
video, text etc. Cryptography is the study of methods ofsending messages in the disguised form to the intendedrecipients. Steganography and cryptography bothtechniques share the common goals and services of
protecting the confidentiality, integrity and availability ofinformation from unauthorized access. In this paper various
steganography and cryptography with their techniques arestudied: Spectrum, Phase coding, RSA (Ron Rivest, AdiShamir and Len Adlemen), DES (Data Encryption
Standard).
Keywords: Steganography, Cryptography, LSB
coding, Parity coding, spread.
1. IntroductionCommunication through internet and digital media
has become an essential part of infrastructure now a
days and it is important that communication be madesecret. As a result, the security of information passed
over an open channel has become a fundamental
issue and therefore, the confidentiality and data
integrity are required to protect against unauthorized
access and use. This has resulted in an unstable
growth in the field of information hiding.
Steganography and cryptography and are the two
popular methods available to provide security [1].
Steganography is the art and science of
communicating in a way which hides the existence of
the communication. Cryptography scrambles amessage so it cannot be understood by the unintended
recipient. Cryptography and Steganography achieve
the same goal using different means [1]. The power
of steganography is in hiding the secret message by
obscurity, hiding its existence in a non-secret file. In
that sense, steganography is different from
cryptography, which involves making the content of
the secret message unreadable while not preventing
non-intended observers from learning about its
existence. Steganography can be applied in various
objects as images, videos, audios etc. Steganography
conceals a message such that it would not draw any
attention and therefore would not raise suspicionsthat a secret communication is taking place[12]. For
this reason, steganography is often regarded as a
stealthy method for transmitting sensitive data into
total secrecy across public channels in such a way
that no one, apart for the communicating parties
namely the original sender and the intended receiver,
can know about the existence of the communication.According to [4] cryptography is not sufficient for
secure communication. Even though both methods
provide security, a study is made to combine both
Cryptography and Steganography methods into one
system for better confidentiality and security.
Combining these two methods together for the
purpose of developing a system, that will improve the
confidentiality and security of the message.
2. Related workProf. Samir Kumar Bandyopadhyay and BarnaliGupta Banik (2012) proposed a new method of
audio steganography using layering approach named
multi-level steganography. In multi-level
setganography two traditional method of
setganography i.e lsb encoding and parity encoding
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were blended in a level based approach to reach the
goal. Multi-Level Steganography has advantage of
difficult decoding and sending two secret messagethrough a single cover object.S.S. Divya, M. Ram
Mohan Reddy (2012) proposed two novel
approaches of substitution technique of audio
steganography that improves the capacity of cover
audio for embedding additional data. Using these
methods, message bits are embedded into multiple
and variable LSBs. These methods utilize upto 7
LSBs for embedding data.Results show that boththese methods improve capacity of data hiding of
cover audio by 35% to 70% as compared to the
standerd LSB algorithm with 4 LSBs used for data
embedding and using RSA as encryption and
decryption techniques for performing cryptography.
R SRIDEVI, DR. A DAMODARAM, DR.SVL.NARASIMHAM( 2009 ) proposed Enhanced
Audio Steganography (EAS) system which is based
on audio Steganography and cryptography that
ensures secure data transfer between the source and
destination. EAS uses most powerful encryption
algorithm in the first level of security, which is very
complex to break. In the second level it uses a more
powerful modified LSB (Least Significant Bit)
Algorithm to encode the message into audio. It
performs bit level manipulation to encode the
message. This proposed system is a good and
efficient method for hiding the data from hackers and
sent to the destination in a safe manner. In thissystem the size of the file is not changed even after
encoding and also suitable for any type of audio file
format. Abikoye Oluwakemi C. Adewole Kayode
S. Oladipupo Ayotunde J. (2012) proposed a data
hiding system based on audio steganography and
cryptography which is proposed to secure data
transfer between the source and destination. Audio
medium is used for the steganography and a LSB
(Least Significant Bit) algorithm is employed to
encode the message inside the audio file.Padmashree G, Venugopala P S (2012) proposes
that steganography works by replacing bits of
useless or unused data in regular computer files (suchas graphics, sound, text, HTML, or even floppy disks
) with bits of different, invisible information. This
hidden information can be plain text, cipher text, or
even images. Audio steganography is a young branch
of this discipline. An encoding mechanism is used for
embedding the message into the audio file. He used
the 4th Bit LSB method to do it. The quality of the
audio file after encoding remains unaffected. A
public key cryptographic algorithm, RSA was also
used to ensure greater security.
3. SteganographySteganography is derived from the Greek wordstegnos (meaning covered/secret) and graphein
(meaning to write/draw). It is the study of means of
concealing the information in order to prevent
hackers from detecting the presence of the secret
information.. Steganography is the form of convert
communication in which a secret message is
camouflaged with a carrier data. Steganography
masks the very presence of communication, making
the true message not discernable to the observer [8].
The main goal or steganography is to communicate
securely in a completely undetectable manner and to
avoid drawing suspicion to the transmission of a
hidden data. The characteristics of these methods areto change in the structure and features of object so as
not to be identifiable by human eye. Digital images,
videos, sound files, and other computer files that
contain perceptually irrelevant or redundant
information can be used as covers or carriers to
hide secret messages. After embedding a secret
message into the cover-image, a so-called stegoimage
is obtained. The basic model of steganography
consists of Carrier, Message, Embedding algorithm
and Stego key. The model for steganography is
shown in Figure 1. Carrier is also known as a cover-
object, which embeds the message and serves to hide
its presences [6]
Fig.1 A model of Steganography
Capacity, security and robustness are three mainaspects of steganography from which its usefulness
and effect can be measured. Capacity refers to the
amount of information that can be hidden in the cover
medium. Security relates to an eavesdroppers
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inability to detect hidden information and robustness
is the amount of modification the stego medium can
withstand before an adversary can destroy the hiddeninformation.[6].
To embed data secretly onto digital audio file there
are few techniques introduced earlier. The lists of
methods are:
LSB Coding Phase Coding Parity Coding Spread Spectrum
3.1 LSB coding
Least significant bit (LSB) coding is the simplest way
to embed information in a digital audio file. In this
technique, LSB of binary equivalent of each sample
of digitized audio file is replaced with a binary
equivalent secret message [2]. By substituting the
least significant bit of each sampling point with a
binary message, LSB coding allows for a large
amount of data to be encoded. In LSB coding, the
ideal data transmission rate is 1 kbps per kHz. Figure
2 illustrates how the message 'HEY' is encoded in a
16-bit CD quality sample using the LSB method.
Fig. 2 Message 'HEY' is encoded in a 16-bit CD
quality sample using the LSB method
To extract a secret message from an LSB encoded
sound file, the receiver needs access to the sequence
of sample indices used in the embedding process.Normally, the length of the secret message to be
encoded is smaller than the total number of samples
in a sound file. One must decide then on how to
choose the subset of samples that will contain the
secret message and communicate that decision to the
receiver[5]. One trivial technique is to start at the
beginning of the sound file and perform LSB coding
until the message has been completely embedded,leaving the remaining samples unchanged. This
creates a security problem, however in that the first
part of the sound file will have different statistical
properties than the second part of the sound file that
was not modified. One solution to this problem is to
pad the secret message with random bits so that the
length of the message is equal to the total number of
samples.
3.2 Phase coding
In phase encoding scheme the phase of carrier file is
replaced with reference phase which represents
hidden data. The basic idea is to split the original
audio stream or cover file(C) into blocks and embed
the whole message data sequence into the phase
spectrum of the first block. One drawback of the
phase coding method is a considerably low payloadbecause only the first block is used for secret
message (M) embedding. In addition, the M is not
distributed over C that means it is localized data
and thus can be removed easily by the cropping
attack. [2]
3.3 Parity coding
Instead of breaking a signal down into individual
samples, the parity coding method breaks a signal
down into separate regions of samples and encodes
each bit from the secret message in a sample region's
parity bit. If the parity bit of a selected region doesnot match the secret bit to be encoded, the process
flips the LSB of one of the samples in the region [1].
3.4 Spread Spectrum
In spread spectrum method secret information is
spread over the audio signal's frequency spectrum as
much as possible. Basically this method calculates
the frequency masking threshold using psycho
acoustic model, data signal is spread by a M-
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sequence code, and the spread signal is embedded in
audio below the frequency masking threshold. M-
sequence codes have good autocorrelation propertieswhere the autocorrelation function has peaks equal to
1 at 0, N, 2N (approximately 1/N elsewhere).
Because of these periodic peaks, the M-sequence
code is self-clocking, so the receiver can easily
synchronize the data frame and retrieve the
embedded data by de-spreading with the same M-
sequence code [9].
4. CryptographyCryptography is the study of methods of sending
messages in disguised form so that only the intended
recipients can remove the disguise and read themessage. It is the practical art of converting messages
or data into a different form, such that no-one can
read them without having access to the 'key'. The
message may be converted using a code or a 'cipher'
or 'cipher' .Cryptology is the science underlying
cryptography [6]. It is a means of converting
information from its normal comprehensible form
into an incomprehensible format, rendering it
unreadable without the secret knowledge. The
process of converting information (plain text) by
transforming it into unreadable format (cipher text) is
known as encryption. Encryption techniques can be
sometimes broken by cryptanalysis, also called ascode breaking, although modern cryptographictechniques are virtually unbreakable[8].
Cryptography encrypts the actual message that is
being sent. This mechanism employs mathematical
schemes and algorithms to scramble data into
unreadable text. It can only be decoded or decrypted
by the party that possesses the associated
key.
There are two main types of cryptography:
Secret key cryptography Public key cryptography
In cryptographic systems, the term key refers to a
numerical value used by an algorithm to alter
information, making that information secure and
visible only to individuals who have the
corresponding key to recover the information.
4.1 Secret key cryptography
This is also known as symmetric key cryptography.With this type of cryptography, both the sender and
the receiver know the same secret code, called the
key. Messages are encrypted by the sender using the
key and decrypted by the receiver using the same
key. This method works well if you are
communicating with only a limited number of
people, but it becomes impractical to exchange secret
keys with large numbers of people. In addition, there
is also the problem of how you communicate the
secret key securely. It includes DES, AES, 3DES,
IDEA, Blowfish algorithms.
4.1.1 DES
It uses block cipher. In this same algorithm and key is
used for encryption and decryption. It encrypts the
data in block size of 64 bits each 8 bits (one octet) of
which are used for parity checks (to verify the key's
integrity). Each of the key's parity bits (1 every 8
bits) is used to check one of the key's octets by odd
parity, that is, each of the parity bits is adjusted to
have an odd number of '1's in the octet it belongs to.
The key therefore has a "useful" length of 56 bits,
which means that only 56 bits are actually used in the
algorithm.
The algorithm involves carrying out
combinations, substitutions and permutations
between the text to be encrypted and the key, while
making sure the operations can be performed in both
directions (for decryption). The combination of
substitutions and permutations is called a product
cipher [10]. This Substitution and Permutation is
done in 16 rounds. In each round key and data bits
are shifted, permuted, XORed and sent through, 8 s-box. In the first round 64 bit plaintext is handed to
initial permutation(IP).Then IP generates two half
left plaintext(LPT)and right plaintext(RPT).Each
LPT and RPT goes through 16 rounds. At the lastLPT and RPT are rejoined. Decryption is same
process perform rounds in reverse order.
4.2 Public key cryptography
It also called asymmetric encryption uses a pair of
keys for encryption and decryption. With public key
cryptography, keys work in pairs of matched public
and private keys. The public key can be freely
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distributed without compromising the private key,
which must be kept secret by its owner. Because
these keys work only as a pair, encryption initiatedwith the public key can be decrypted only with the
corresponding private key. It includes RSA, Digital
Signature and Message Digest algorithms.
4.2.1 RSA
This is public key encryption algorithm developed by
Ron Rivest, Adi Shamir and Len Adlemen in 1977. It
is most popular and asymmetric key cryptographic
algorithm. It may used to provide both secrecy and
digital signature. It uses the prime no. to generate the
public and private key based on mathematical fact
and multiplying large numbers together. It uses theblock size data in which plaintext and cipher text are
integers between 0and n1 for some n values. Size of n
is considered 1024bits or 309 decimal digits. In this
two different keys are used for encryption and
decryption purpose. As sender knows encryption key
and receiver knows decryption key [4].
The arithmetic calculations of the algorithm:
1. Choose one number and divide it to twoprime numbers.
2. Select p and q.3. Calculate n=p*q.4. Calculate Z=(p-1)(q-1)5. Select integer e which is relatively prime
to 2. (Z=(n))
6. Calculate e*d=1 Mod((n)) and determined.
7. Public key = {e, n} and private key={d, n}8. For Data Encryption:
c=M^e Mod n.
9. For Data Decryption :M=c^d Mod n.
5. ConclusionsSteganography and Cryptography with their
techniques are studied for information security.
Steganography is the method of data hiding whereas
cryptography is an encryption technique. In
comparison to other steganographic techniques LSB
modification algorithm is simple and effective. RSAand DES techniques of cryptography are studied in
detail and it studies shows that DES is better than
RSA. Both steganography and cryptography are
information security techniques and when they are
combined together security can be enhanced many
times. As a future work an algorithm combining both
techniques can be proposed for data security.
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