This paper proposed a novel cryptography method for enhancing the user level security to avoid malicious user entering into cloud applications. Existing research works have been proposed various cryptographic methods, algorithms and techniques for validating the user for accessing data or operating cloud applications. But still the malicious user activity like sybil, sinkhole, Denial of Service, Distributed Denial of Service, Economic Denial of Sustainability, selective forwarding and so on, is increasing day by day in cloud. This paper taken this problem as a major problem and motivated to provide a better solution which can eliminate the malicious user activity in cloud. To do this, this paper used DNA cryptography method for generating a strong key for user and data encryption – decryption process. User information is converted into human deoxyribonucleic acid form for generating strong key and data encryption. The implementation of the proposed approach is carried out in DOTNET framework and the experimental results are verified. Based on the results the performance is evaluated by comparing with the existing results.