Encrypts data with an asymmetric key.
Encryption and decryption with an asymmetric key is very costly compared with encryption and decryption with a symmetric key. We recommend that you not encrypt large datasets, such as user data in tables, using an asymmetric key. Instead, you should encrypt the data using a strong symmetric key and encrypt the symmetric key using an asymmetric key.
EncryptByAsymKey return NULL if the input exceeds a certain number of bytes, depending on the algorithm. The limits are: a 512 bit RSA key can encrypt up to 53 bytes, a 1024 bit key can encrypt up to 117 bytes, and a 2048 bit key can encrypt up to 245 bytes. (Note that in SQL Server, both certificates and asymmetric keys are wrappers over RSA keys.)
The following example encrypts the text stored in @cleartext with the asymmetric key JanainaAsymKey02. The encrypted data is inserted into the ProtectedData04 table.
INSERT INTO AdventureWorks2012.Sales.ProtectedData04 VALUES( N'Data encrypted by asymmetric key ''JanainaAsymKey02''', EncryptByAsymKey(AsymKey_ID('JanainaAsymKey02'), @cleartext) ); GO