Symmetric and asymmetric keys both are used to make transactions secured. Both are the complete solution to avoid data loss and have different advantages. The goals can be achieved by applying both techniques in the proper way and in the appropriate situation. Both are used to encrypt data using the same keys. The sender and receiver of the information are informed about the keys. The difference arises in their functionality and efficiency.          Symmetric keys are faster because their algorithm takes far less time to execute. Faster working makes it more efficient than asymmetric keys. Due to its efficiency, it is used to process big data efficiently. It is used where speed is required.  The symmetric encryption uses the same key for the encryption and decryption of data. This is why it is a very simple and cheaper technique. It is the disadvantage of using a symmetric key that all the persons involved in this encryption are given the key used for encryption.          The asymmetric keys are less efficient as they take more time than symmetric keys. Asymmetric keys use two keys: a public key and a private key. The first key encrypts data but the second one decrypts the encrypted information. It is useful where many persons are sharing information. A person gives his information by a public key and the information can be only read by the person who has the private key of that data. So in this way information is secured. The public key can be given to any person to deliver the message. But the private key is given only to the relevant person. It is expensive to use the asymmetric key.References

Daniel J. Bernstein (1 May 2008). “Protecting communications against forgery” (PDF). Algorithmic Number Theory. 44. MSRI Publications. §5: Public-key signatures, pp. 543–545. Retrieved 14 November 2016.

Rivest, R.; Shamir, A.; Adleman, L. (February 1978). “A Method for Obtaining Digital Signatures and Public-Key Cryptosystems” (PDF). Communications of the ACM. 21 (2): 120–126. CiteSeerX 10.1.1.607.2677. doi:10.1145/359340.359342.