Parameterization(Always Encrypted)- Inside stored proc

Question

I have a scenario where i need to have literals(hard coded strings) inside proc used against "Always Encrypted" columns, Since this fails with the following error,

Operand type clash: varchar is incompatible with nvarchar(20) encrypted with (encryption_type = 'DETERMINISTIC', encryption_algorithm_name = 'AEAD_AES_256_CBC_HMAC_SHA_256', column_encryption_key_name = 'CEK_Auto4', column_encryption_key_database_name = 'DBName')

I am trying to do Parameterization for Always Encrypted within the stored proc, similar to below

GO
    CREATE PROCEDURE InsertProc  
    @Var1 nVarchar(20)  
    As  
    BEGIN     
        DECLARE @Plaintext nvarchar(20)='testText' 

        INSERT INTO testClass(EncryptedCol1,EncryptedCol2,NonEncryptedCol)
        VALUES (@Plaintext,@Var1,default)
    END

I have also enabled parameterization and also enabled column encryption setting for connection. Still getting the following error when creating procedure,

Procedure sp_describe_parameter_encryption, Line 1 [Batch Start Line 4] Statement(s) could not be prepared. An error occurred while executing batch. Error message is: Internal error. Metadata for parameter '@p3467a2cdc3d547a3be48f46dfc7e9580' in statement or procedure<--my proc code here--> ' is missing in resultset returned by sp_describe_parameter_encryption.

NOTE:I still could execute and insert if i manually run the script which is inside the proc.But Proc creation is issue

Could some one help to fix or provide alternative solution.

Answer 1

I found a work around for using hard coded strings in procedures.

1. Create a table with a nVarchar column(Note: encrypted nvarchar is not compatable with encrypted varchar, Also you could not assign value from higher data length to lower data length encrypted values(Eg you could not assign a encrypted variable/column of nVarchar(max) to a encrypted column of nVarchar(20)). So choose a smaller size as possible.)
2. Encrypt the column with the same encryption type and key as that of the column under consideration.
3. Now you could use the value from the table to insert, update, compare,..etc. operations. You could also use in functions like coalesce , isnull, etc..

Example:

Create table with encrypted column

CREATE TABLE [dbo].[Encrypted_nVarchar_256](
    [SNo] [smallint] IDENTITY(-32768,1) NOT NULL,
    [EncryptValue] [nvarchar](256) COLLATE Latin1_General_BIN2 
ENCRYPTED WITH (COLUMN_ENCRYPTION_KEY = [CEK_key], ENCRYPTION_TYPE = Deterministic, ALGORITHM = 'AEAD_AES_256_CBC_HMAC_SHA_256') NULL,
        [Value_Description] [nvarchar](256) NULL,
     CONSTRAINT [Pk_Enc_nVar_256] PRIMARY KEY CLUSTERED 
    (
        [SNo] ASC
    )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
    ) ON [PRIMARY]
    GO

Insert text into encrypted column the value that you would required to be used inside procedures.

DECLARE @EncryptValue  nvarchar(256) ='';
INSERT INTO Encrypted_nVarchar_256(EncryptValue,[Value_Description]) VALUES(@EncryptValue,'Empty string')
DECLARE @EncryptValue1  nvarchar(256) ='Some string you would like to hard code';
INSERT INTO Encrypted_nVarchar_256(EncryptValue,[Value_Description]) VALUES(@EncryptValue1,'Your description')
--more rows as you need
GO

Now you could consume in stored procedure

 CREATE PROCEDURE InsertProc  
    @Var1 nVarchar(20)  
    As  
    BEGIN    
        --Passing hard coded ''(Empty string) as insert value
        INSERT INTO testTable(EncryptedCol1,EncryptedCol2,NonEncryptedCol)
        SELECT TOP 1 EncryptValue,@Var1,"some string" FROM Encrypted_nVarchar_256 where Sno=-32768
        --Comparing some hard coded string
        SELECT * from  testTable
        where EncryptedCol1=(SELECT TOP 1 EncryptValue FROM Encrypted_nVarchar_256 
 where Sno=-32768)
         --Using in functions
         SELECT COALESCE(EncryptedCol1,(SELECT TOP 1 EncryptValue FROM Encrypted_nVarchar_256  where Sno=-32768)) as [new col name] from  testable

    END

Voila!!! now you could do anything with just a little twist.