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Public Key Cryptosystem

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A. RSA
RSA stands for Ron Rivest, Adi Shamir and Leonard Adleman. It is a public key Cryptosystem used for secure data transmission. In this, two different keys are used. One is public key used for encryption and other is private key used for decryption. In [1], they mainly focused on the data security issues in the cloud like:
1) Privacy and Confidentiality which means that once the user hosted the data in the cloud, there should be some guarantee that access to that hosted data will only be limited to the authorized access. It is ensured by the authentication services, security protocols and data encryption services.

2) Data Integrity which means data sent is same as the message received i.e. it is not altered in between. It is ensured by the firewalls and intrusion detection system (IDS).

3) Data Availability which means data should be available to users when they needed.

4) Data Location and Relocation which means data can be moved from one location to another because cloud providers have contracts with each other, so that they can use each other’s resources.

In cloud computing environment, plain text is converted into cipher text by the cloud service provider and get back to the original data by the cloud user. Only the authorised user can access the data. If any unauthorised person gets the data intentionally or by mistake then he cannot get the original data.
In [2], they have addressed the secure hybrid framework to ensure the data security in cloud computing, which comprises public key algorithm RSA, private key algorithm AES and SHA algorithm which is used to convert arbitrary sized message into hash code with the help of hash function. They have integrated digital fingerprint mechanism to enhance the authenticatio...

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... is generated using secure hash algorithm which is combined with digital signature to form a concatenated string. This concatenated string is then encrypted with the help of public key of receiver and sent to the cloud user who requested data. Then deciphered message is converted into the message digest by SHA for data integrity verification and RSA is used to validate digital fingerprint.
1) Advantages: It produces a fixed length output by applying a hash function on the actual data. So, it’s easy to compute fixed length output. It is a collision resistant algorithm and provides a one way hash. Its attack protection is also stronger than the other algorithms.
2) Disadvantages: It is a slower computational algorithm than MD5 algorithm. It has known security vulnerabilities. Choosing an effective hash function for a specific application is a difficult task.
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