Information Security using Cryptography and Steganography

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Information Security using Cryptography and Steganography

Neetha Francis,

Asst. Professor, Dept. of Computer Science,

Pazhassi Raja College, Pulpally

Abstract- In todays information technology era, the internet is an essential part for communication and information sharing. Providing confidential information and establishing concealed association has been a great interest since long time ago. 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. Cryptography and steganography are the two popular methods available to provide security. Cryptography scrambles a message so it cannot be understood and generates cipher text. Steganography word is derived from Greek, literally means Covered Writing. Steganography is the art of hiding the existence of data in another transmission medium to achieve secret communication. It does not replace cryptography but rather boosts the security using its obscurity features. It includes vast ways of secret communications methods that conceal the messages existence. In Cryptography, the meaning of data has been changed. So, it makes intention to the hacker to hack or destroy the data. In our proposed paper, we implement a method by integrating both Cryptography and Steganography for information security. It not only changes the meaning of data but also hides the presence of data from the hackers. In order to secure the transmission of data, Steganography has to be implemented that allow information to be sent in a secure form in such a way that the only person able to retrieve this information is intended recipient.

Keywords: – Cryptography, Steganography, LSB, Data hiding, Stego-image, Diffie-Hellman Key Exchange


Cryptography and Steganography are well known and widely used techniques that manipulate information in order to cipher or hide their existence respectively. Steganography is the art and science of communicating in a way which hides the existence of the communication. Cryptography scrambles a message so it cannot be understood; Steganography hides the message so it cannot be seen. 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.

Cryptography systems can be broadly classified into symmetric-key systems that use a single key that both the sender and the receiver have, and public-key systems that use two keys, a public key known to everyone and a private key that only the recipient of messages uses. In

Cryptography, a cipher message for instance, might arouse suspicion on the part of the recipient while an invisible message created with steganographic methods will not. However, steganography and cryptography differ in the way they are evaluated: steganography fails when the enemy is able to access the content of the cipher message, while cryptography fails when the enemy detects that there is a secret message present in the steganographic medium. The disciplines that study techniques for deciphering cipher messages and detecting hidden messages are called cryptanalysis and steganalysis. The former denotes the set of methods for obtaining the meaning of encrypted information, while the latter is the art of discovering covert messages. The aim of this paper is to describe a method for integrating cryptography and steganography through some media such as image, audio, video, etc.

Cryptography and Steganography are often interrelated and share the common goals and services of protecting the confidentiality, integrity and availability of information; which are some of the most important fields in computer security. Cryptography and steganography are methods of transferring private information and data through open network communication, so only the receiver who has the secret key can read the secret messages which might be documents, images or other forms of data. Cryptography and steganography also contribute to Computer Science, particularly, in the techniques used in computer and network security for access control and information confidentiality. They are also used in many applications encountered in everyday life. Despite the differences between Cryptography and Steganography systems the requests for them have increased recently for the fast development of the Internet publicly.


Cryptography has followed man through many stages of evolution. Cryptography can be found as far back as 1900

B.C. in ancient Egyptian scribe using non-standard hieroglyphics in an inscription. From 500 600 B.C. Hebrew scribes used ATBASH, a reversed alphabet simple solution cipher. From 50 – 60 B.C. Julius Caesar used a simple substitution with the normal alphabet in government communications. Cryptography continued through history with many variations. Today cryptography has reached a new level, quantum cryptography. Quantum cryptography

combines physics and cryptography to produce a new cryptosystem that cannot be defeated without the sender and receiver having the knowledge of the attempted and failed intrusion. Through the long history of cryptography, steganography was developed and flourished on its own.

Steganography comes from the Greek steganos (covered or secret) and -graphy (writing or drawing). Steganography can be defined as the hiding of information by embedding messages within other, seemingly harmless messages, graphics or sounds. The first steganographic technique was developed in ancient Greece around 440

B.C. The Greek ruler Histaeus employed an early version of steganography which involved: shaving the head of a slave, tattooing the message on the slaves scalp, waiting for the growth of hair to disclose the secret message, and sending the slave on his way to deliver the message. The recipient would have the slaves head to uncover the message. The recipient would reply in the same form of steganography.


    Cryptography is the study of mathematical techniques related to aspects of information security such as confidentiality, data integrity, entity authentication, and data origin authentication. In addition, Cryptography is also known as the science of secret writing. The goal of cryptography is to make data unreadable by a third party. Cryptography algorithms are divided into symmetric (secret-key) and asymmetric (public-key) network security protocols. Symmetric algorithms are used to cipher and decipher original messages (plaintext) by using the same key. While Asymmetric algorithms uses public-key cryptosystem to exchange key and then use faster secret key algorithms to ensure confidentiality of stream data. In Public-key encryption algorithms, there is a pair of keys, one key is known to the public, and is used to encrypt information to be sent to a receiver who owns the corresponding private key. The private and public keys are both different and need for key exchange.

    Fig. 1: Cryptographic system

    Cryptographic systems are generically classified along three independent dimensions.

    1. Methodology for transforming plain text to cipher text All encryption algorithms are based on two general principles: substitution, in which each element in the plaintext is mapped into another element, and

      transposition, in which elements in the plaintext are rearranged. The fundamental requirement is that no information be lost.

    2. Methodology for number of keys used

      There are some standards methods which is used with cryptogaphy such as secret key, public key, digital signature and hash function.

      Digital Signature: The use of digital signature came from the need of ensuring the authentication. The digital signature is more like stamp or signature of the sender which is embedded together with the data and encrypts it with the private key in order to send it to the other party. In addition, the signature assures that any change made to the data that has been signed is easy to detect by the receiver.

      Hash Function: The hash function is a one way encryption, the hash function is a well defined procedure or mathematical formula that represents a small size of bits which is generated from a large sized file, the result of this function can be called hash code or hashes. The generating of hash code is faster than other methods which make it more desired for authentication and integrity. Cryptographic hash functions are much used for digital signature and cheap constructions are highly desirable. The use of cryptographic hash functions for message authentication has become a standard approach in many applications, particularly internet security protocols. The authentication and the integrity considered as main issues in information security, the hash code can be attached to the original file then at any time the users are able to check the authentication and integrity after sending the secure data by applying the hash function to the message again and compare the result to the sender hash code, if its similar that is mean the message came from the original sender without altering because if there is any changed has been made to the data will changed the hash code at the receiver side.

    3. Methodology for processing plain text

      A block cipher processes the input one block of elements at a time, producing an output block for each input block. A stream cipher processes the input elements continuously, producing output one element at a time, as it goes along.


    Steganography is the science of writing hidden messages to guarantee information which is accessible only by authorized parties. It is the practice of hiding information usually text messages, inside other files (host files). The practice of hiding information is called stego. Information can be hidden or embedded inside any type of multimedia files especially image files. The host files can then be exchanged over an insecure medium without anyone knowing what really lies inside them. Therefore, steganography in contrast with cryptography, where the existence of the message is clear, but the meaning is obscured. Steganography applications conceal information

    in other, seemingly innocent media. Steganographic results may masquerade as other file for data types, be concealed within various media, or even hidden in network traffic or disk space. Information hiding techniques provide an interesting challenge for digital forensic investigations. Information can easily traverse through firewalls undetected.

    Fig. 2: Steganographic system


    Coding secret messages in digital images is the most widely used of all methods in the digital world. This is because it can take advantage of the limited power of the human visual system (HVS). Almost any plain text, cipher text, image and any other media that can be encoded into a bit stream can be hidden in a digital image. With the continued growth of strong graphics power in computers and the research being put into image based Steganography, this field will continue to grow at a very rapid pace.

    As Duncan Sellars explains:"To a computer, an image is an array of numbers that represent light intensities at various points, or pixels. These pixels make up the images raster data.". 24-bit image files are considered as carrier media candidates for hiding information in our proposed method of study. One of those methods is Least Significant Bit (LSB) Method. LSB insertion is an approach of embedding information in a cover image. The least significant bit of some or all bytes inside an image is changed to bits of the secret message. When using a 24-bit image, a bit of each of the red, green and blue color components can be used, since they are represented by a byte. In other words one can store 3 bits in each pixel. For example, a grid of 3 pixels of a 24-bit image is as follows:

    ( 00101101 00011100 11011100 )

    ( 10100110 11000100 00001100 )

    ( 11010010 10101101 01100011 )

    When the number 200, for which binary representation is 11001000, is embedded into the least significant bits of this part of this image, the resulting grid is as follows:

    ( 00101101 00011101 11011100 )

    ( 10100110 11000101 00001100 )

    ( 11010010 10101100 01100011 )

    Although the number was embedded into the first 8 bytes of the grid, only 3 underlined bits are changed according to the embedded message. On average, only half of the bits in an image will need to be modified to hide a secret message. Since there are 256 possible intensities of each primary color, changing the LSB of a pixel results in small changes in the intensity of the colors. These changes cannot be perceived by the human eye- thus the message is successfully hidden. With a well chosen image, one can even hide the message in the least as well as second to least significant bit and still not see the difference.

    In the above example, consecutive bytes are used to embed the information. This approach is very easy to detect. A slightly more secure system is to share a secret key which specifies which pixels to be changed between sender and receiver. This process needs a secret key called the stego-key. This key is used to control the process such as the selection of pixels. The selected pixels will then be used to embed secret binary information.


During the early history of cryptography, two parties would rely upon a key using a secure, but non- cryptographic, method; for example, a face-to-face meeting or an exchange via a trusted courier. This key, which both parties kept absolutely secret, could then be used to exchange encrypted messages. A number of significant practical difficulties arise in this approach of distributing keys. Public-key cryptography addresses these drawbacks so that users can communicate securely over a public channel without having to agree upon a shared key beforehand. An asymmetric-key cryptosystem was published in 1976 by Whitfield Diffie and Martin Hellman, who, influenced by Ralph Merkle's work on public-key distribution, disclosed a method of public-key agreement. This method of key exchange, which uses exponentiation in a finite field, came to be known as DiffieHellman key exchange. The Diffie-Hellman key exchange protocol was the first system to utilize public-key or two-key cryptography. For this reason, it is sometime called as Asymmetric encryption. This was the first published practical method for establishing a shared secret-key over an authenticated (but not private) communications channel without using a prior shared secret.

Public-key Cryptography:

Public-key cryptography refers to a cryptographic system requiring two separate keys, one to lock or encrypt the plaintext, and one to unlock or decrypt the cipher-text. Neither key will do both functions.

Fig. 3: Public key Cryptography

One of these keys is published or public and the other is kept private. If the lock/encryption key is the one published then the system enables private communication from the public to the unlocking key's owner. If the unlock/decryption key is the one published then the system serves as a signature verifier of documents locked by the owner of the private key. In the DiffieHellman key exchange scheme, each party generates a public/private key pair and distributes the public key. After obtaining an authentic copy of each other's public keys, SENDER and RECIPIENT can compute a shared secret offline.

An analog that can be used to understand the advantages of an asymmetric system is to imagine two people, SENDER and RECIPIENT, sending a secret message through the public mail. In this example, SENDER wants to send a secret message to RECIPIENT, and expects a secret reply from RECIPIENT. With a Symmetric-key system, SENDER first puts the secret message in a box, and locks the box using a padlock to which he has a key. He then sends the box to RECIPIENT through regular mail. When RECIPIENT receives the box, he uses an identical copy of SENDER's key (which he has somehow obtained previously, maybe by a face-to-face me send his secret reply. In an Asymmetric-key system, RECIPIENT and SENDER have separate padlocks. First, SENDER asks RECIPIENT to send his open padlock to him through regular mail, keeping his key to himself. When SENDER receives it he uses it to lock a box containing his message, and sends the locked box to RECIPIENT. RECIPIENT can then unlock the box with his key and reads the message from SENDER. To reply, RECIPIENT must similarly get SENDER's open padlock to lock the box before sending it back to her. The critical advantage in an asymmetric key system is that RECIPIENT and SENDER never need to send a copy of their keys to each other. This prevents a third party (perhaps, in the example, a corrupt postal worker) from copying a key while it is in transit, allowing said third party to spy on all future messages sent between SENDER and RECIPIENT. So in the public key scenario, SENDER and RECIPIENT need not trust the postal service as much. In addition, if

RECIPIENT was careless and allowed someone else to copy his key, SENDER's messages to RECIPIENT would be compromised, but SENDER's messages to other people would remain secret, since the other people would be providing different padlocks for SENDER to use. Public key exchange cryptosystem eliminates the key distribution problem by using two keys, a private and a public key. By exchanging the public keys, both parties can calculate a unique shared key, known only to both of them.

The Diffie-Hellman Algorithm for Key Exchange

SENDER must do the following:

    1. Choose a prime numbers p randomly, and choose two integer numbers a and g.

    2. Compute the A (SENDER's public key), as follows: A = ga mod p.

    3. Send the public value A to RECIPIENT.

    4. Compute the secret value K, as follows:

K = Ba mod p.

RECIPIENT must do the following:

  1. Choose an integer numbers b randomly.

  2. Compute the B (RECIPIENT's public-key), as follows: B = gb mod p.

  3. Send the public value B to SENDER.

  4. Compute the secret value K, as follows:

K = Ab mod p.


Steganography is not the same as cryptography Data hiding techniques have been widely used to transmission of hiding secret message for long time. Ensuring data security is a big challenge for computer users. Business men, professionals, and home users all have some important data that they want to secure from others. Even though both methods provide security, to add multiple layers of security it is always a good practice to use Cryptography and Steganography together. By combining, the data encryption can be done by a software

and then embed the cipher text in an image or any other media with the help of stego key. The combination of these two methods will enhance the security of the data embedded. This combined chemistry will satisfy the

requirements such as capacity, security and robustness for secure data transmission over an open channel. A pictorial representation of the combined concept of cryptography and steganography is depicted in figure 4.

Fig. 4: Combination of Cryptography and Steganography

In figure 4, both the methods are combined by encrypting message using cryptography and then hiding the encrypted message using steganography. The resulting stego-image can be transmitted without revealing that secret information is being exchanged. Furthermore, even if an attacker were to defeat the steganographic technique to detect the message from the stego-object, he would still require the cryptographic decoding key to decipher the encrypted message. Since then, the steganography approaches can be divided into three types.

Pure Steganography: This technique simply uses the steganography approach only without combining other methods. It is working on hiding information within cover carrier.

Secret Key steganography: The secret key steganography use the combination of the secret key cryptography technique and the steganography approach. The idea of this type is to encrypt the secret message or data by secret key approach and to hide the encrypted data within cover carrier.

Public Key Steganography: The last type of steganography is to combine the public key cryptography approach and the steganography approach. The idea of this type is to encrypt the secret data using the public key approach and then hide the encrypted data within cover carrier.


The proposed method describes two steps for hiding the secret information by using the public steganography based on matching method in different regions of an image.

  • The First step is converting the Plain text message into cipher text using Public-key Encryption algorithm.

  • The next step is to find the shared stego-key between the two communication parties (SENDER & RECIPIENT) over insecure networks by applying Diffie-Hellman Key exchange protocol (as explained above). At the end the protocol, each side recovers his/her received public key to reach the shared values between them, thats mean SENDER & RECIPIENT have arrived same sego-key value.

  • The next step in the proposed method is that the sender uses the secret stego-key to select pixels that it will be used to hide.


Ensuring data security is a big challenge for computer users. Businessmen, professionals, and home users all have some important data that they want to secure from others. Even though both methods provide security, to add multiple layers of security it is always a good practice to use Cryptography and Steganography together. The present study is designed to combine the features of both cryptography and steganography, which will provide a higher level of security. It is better than the technique used separately. Simple LSB method was used to embed the secret message into the image. The LSB in each selected pixel can be used to conceal the message binary code. It is also found that combination of cryptography and steganography enhance the security and reliability of message as first message is encrypted and using steganography hide it to other carrier like digital image, video file or any other.


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