Secret message passing through an open channel needs an extreme level of privacy to protect it from theft or misuse. To achieve this objective, two parallel approaches are frequently used in digital media namely – Cryptography and Steganography. Cryptography encrypts the secret data into some unreadable format before sending through shared channel whereas Steganography conceals the secret message within an ordinary, non-secret file in such a way that an eavesdropper cannot suspect its existence. One layer of security, however, may be vulnerable from various security attacks. Hence, both the methods can be combined to achieve more secure as well as powerful model termed as Crypto-stego model. In this paper, an extensive survey is presented on Stegano-encryption techniques that are applied to various real-world systems which need high security. The survey also provides a thematic approach to classify available state-of-the-arts with regards to different application domains where it could be used. The rigorous survey follows the security threats along with various security-analysis that can establish a system as robust and safe from attacks.

Keywords: Steganography, Cryptography, Security, Robust-system, Steganalysis
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