IV.SECUTIRY TECHNIQUESIn the present era various number ofapplications are relying on internet such online shopping , stock trading,internet banking, digital bill payment etc., All these public networks need tohave the end to end  connection in asecured manner which should also be confidential in order to ensure dataauthentication, confidentiality ,availability integrity as well as accountability.As per NIST  computer security can be defined as theprotection afforded to an automated information system in order to attain theapplicable objectives of preserving the integrity ,availability ofconfidentiality of information system resources(inclusion hardware, software,firmware ,data /information and tele-communications)Security is the process of protectingthe services and information from an unauthorised access, modification ordistruction . In networking the security can be obtained by using cryptography (oneof  science and art) is  of transforming the messages  so thatthey can be protected by attacks.Encryption is one of important mechanism which can ensure the security of sensitiveinformation. The  encryption algorithmsare classified into two groups: symmetric key(secret key) and asymmetrickey(public key)579Symmetric key: it is also known as conventional encryption is a form of cryptosystemin which encryption and decryption performed using same key57 9Asymmetric encryption : In which encryption and decryptionare performed using the different keys ie.

, public key, private key.5 9V.EXISTING ALGORITHMS FOR SECURITY In data communication encryption plays a major role to secure the data. Theencryption algorithms714 used in cloud computing are 1.Symmetric encryption algorithms:                In this method sender andreceiver use a single secret key which is used to encrypt and decrypt themessages. Some of the encryption algorithms area)      DES(DataEncrytpion Standard): It is a symmetric key algorithm used to encryptthe information. It was developed by IBM in 1975.

In DES algorithm block cipheris of 64bits and key is of 56bits. Now a days this algorithm is insecure forlots of applications.514b)      3DES(TrippleData Encryption algorithm): It is developed to overcome the flaws of DESwithout  designing a new crypto system. Itwas developed by IBM in 1978.

3DES extends the key size of DES by applying thealgorithm 3 times in succession with 3 different keys. The combined key size isthus 168 bits( 3times to DES(3*56)).TDEA uses three 64bit keys K1,K2,K3 inEncrypt-Decrypt-Encrypt(EDE) mode.

3DES is slower than other block ciphermethods.514c)      AES(AdvancedEncyrption Standard): Is one of the new encryption standard recommendedby NIST to replace DES in 2001. AES can support any combination of data(128bits ) and key length of 128,192 and 256 bits. During encryption anddecryption process AES goes through 10 rounds for 128 bit keys, 12 rounds for192 bit keys and 14 rounds for 256 bit keys to deliver final cipher text. Thedraw back of this algorithm is difficult to implement.

57d)      BlowFish:Isa symmetric key algorithm designed by Bruce Schneier in the year 1993. It is abasic algorithm developed an option to DES algorithm to  overcome many problems that come with manyother algorithms. This algorithm is available in public domain. And can beavailable to free to every one.7.The key size is 32-448 bits and 16 rounds.e)      RC5(RivestCipher):  Is a symmetric key algorithm.

Mainly known for its simple execution. This is developed by Ronald Rivest in1994. The speed of algorithm is slow comparative to other algorithms 2.Asymmetric Algorithms:                These  are public key algorithms which generallymake use of different keys for encryption and decryption. These algorithms aremost important because these can be used for transmission of encryption keys.a) RSA(Rivest-Shamir-Adeleman): Is the most simple and common asymmetricalgorithm used for both encryption and decryption of digital signature. It hasfast encryption key.

514. . It was developed by Ronrivest,Adi shamir,andLeonard Adleman in 1978.

     b) DSA :  It is an important algorithm forprocessing the digital data. It was given by the NIST in the year august 1991.c) Diffie-Hellman : Is the earlierasymmetric data standard algorithm developed in the year 1976. This algorithmmost widely used   key exchange algorithm14  VI.

CONCLUSIONCloud computing provides an enormous benefits of cloud services andresources in various fields. However cloud security issues remain the majorobstacles  that may prohibit the adoptionof cloud computing on a large scale.  Securityengineering is one of the best practices to provide the best methods andtechniques for developing systems and services which are built for security, sustainabilityand resiliency. In this paper the  overview of various  security threats, attacks with solutions, securityissues , challenges , risks and   some of the encryption techniques werediscussed.