Symmetric ciphers use a single key for both encrypting and decrypting data.
In this case , the encrypted data is secure only if the key can be securely distributed to both parties. In asymmetric encryption a key pair, consisting of a public key and private key, is used to encrypt and decrypt data. The public key encrypts, but cannot be used to decrypt. Only the private key can decrypt the data, thus data encoded with the public key is secure as long as the private key stays secure. Used alone, both ciphers have their shortcomings.