Cloud is the Internet based computing that provides resources on-demand. This has become an attractive solution to data owners as the can outsource data and computing. There is potential risk in terms of security and privacy of the outsourced data as the cloud servers are treated untrusted. In this context, there are two security mechanisms that are widely used. They are known as cryptography and steganography. The cryptography converts data into some format that cannot be comprehended by humans while the steganography hides the presence of a message (may be encrypted one) in an image or any digital media. If both are used independently they have their own limitations. When both are combined, it forms a realizable mechanism with both security and secrecy. Thus, the Crypto-steganography is the approach that overcomes the limitations of individual mechanisms as it proves to be difficult to adversaries to launch attacks. In this paper an LSB substitution method and quadruple efficient image encryption method are used to secure sensitive messages when they are outsourced to public cloud. We built a prototype application to show the utility of the proposed hybrid method. The results revealed that the proposed is capable of increasing security to the data outsourced to public cloud.

Cloud computing, cryptography, steganography, crypto-steganography

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