Hi mdali,
Refer the below query. You need to use the same key to decrypt the encrypted string.
DECLARE @Encrypt VARBINARY(200)
SET @Encrypt = ENCRYPTBYPASSPHRASE('MAKV2SPBNI99212', 'abc')
SELECT @Encrypt EncryptedValue
SELECT CONVERT(VARCHAR(100),DECRYPTBYPASSPHRASE('MAKV2SPBNI99212', @Encrypt)) DecryptedValue
Output
EncryptedValue
0x01000000083E19A4BF8EAAF20B3B25092522E19439003A7D8FA816CD
DecryptedValue
abc