CERTENCODED (Transact-SQL)

Artikel
09/03/2024

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

This function returns the public portion of a certificate in binary format. This function takes a certificate ID as an argument, and returns the encoded certificate. To create a new certificate, pass the binary result to CREATE CERTIFICATE ... WITH BINARY.

Syntax

CERTENCODED ( cert_id )

Arguments

cert_id
The certificate_id of the certificate. Find this value in sys.certificates; the CERT_ID (Transact-SQL) function will return it as well. cert_id has data type int.

Return types

varbinary

Remarks

Use CERTENCODED and CERTPRIVATEKEY together to return, in binary form, different portions of a certificate.

Permissions

CERTENCODED is publicly available.

Examples

Simple Example

This example creates a certificate named Shipping04, and then uses the CERTENCODED function to return the binary encoding of the certificate. This example sets the certificate expiry date to October 31, 2040.

CREATE DATABASE TEST1;
GO
USE TEST1
CREATE CERTIFICATE Shipping04
ENCRYPTION BY PASSWORD = 'pGFD4bb925DGvbd2439587y'
WITH SUBJECT = 'Sammamish Shipping Records',
EXPIRY_DATE = '20401031';
GO
SELECT CERTENCODED(CERT_ID('Shipping04'));

B. Copying a Certificate to Another Database

The more complex example creates two databases, SOURCE_DB and TARGET_DB. Then, create a certificate in SOURCE_DB, and then copy the certificate to the TARGET_DB. Finally, demonstrate that data encrypted in SOURCE_DB can be decrypted in TARGET_DB using the copy of the certificate.

To create the example environment, create the SOURCE_DB and TARGET_DB databases, and a master key in each database. Then, create a certificate in SOURCE_DB.

USE master;  
GO  
CREATE DATABASE SOURCE_DB;  
GO  
USE SOURCE_DB;  
GO  
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'S0URCE_DB KEY Pa$$W0rd';  
GO  
CREATE DATABASE TARGET_DB;  
GO  
USE TARGET_DB  
GO  
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'Pa$$W0rd in TARGET_DB';  
GO  
  
-- Create a certificate in SOURCE_DB  
USE SOURCE_DB;  
GO  
CREATE CERTIFICATE SOURCE_CERT WITH SUBJECT = 'SOURCE_CERTIFICATE';  
GO

Next, extract the binary description of the certificate.

DECLARE @CERTENC VARBINARY(MAX);  
DECLARE @CERTPVK VARBINARY(MAX);  
SELECT @CERTENC = CERTENCODED(CERT_ID('SOURCE_CERT'));  
SELECT @CERTPVK = CERTPRIVATEKEY(CERT_ID('SOURCE_CERT'),  
       'CertEncryptionPa$$word');  
SELECT @CERTENC AS BinaryCertificate;  
SELECT @CERTPVK AS EncryptedBinaryCertificate;  
GO

Then, create the duplicate certificate in the TARGET_DB database. Modify the following code for this to work, inserting the two binary values - @CERTENC and @CERTPVK - returned in the previous step. Don't surround these values with quotes.

-- Create the duplicate certificate in the TARGET_DB database  
USE TARGET_DB  
GO  
CREATE CERTIFICATE TARGET_CERT  
FROM BINARY = <insert the binary value of the @CERTENC variable>  
WITH PRIVATE KEY (  
BINARY = <insert the binary value of the @CERTPVK variable>  
, DECRYPTION BY PASSWORD = 'CertEncryptionPa$$word');  
-- Compare the certificates in the two databases  
-- The two certificates should be the same   
-- except for name and (possibly) the certificate_id  
SELECT * FROM SOURCE_DB.sys.certificates  
UNION  
SELECT * FROM TARGET_DB.sys.certificates;

This code, executed as a single batch, demonstrates that TARGET_DB can decrypt data originally encrypted in SOURCE_DB.

USE SOURCE_DB;  
  
DECLARE @CLEARTEXT nvarchar(100);  
DECLARE @CIPHERTEXT varbinary(8000);  
DECLARE @UNCIPHEREDTEXT_Source nvarchar(100);  
SET @CLEARTEXT = N'Hello World';  
SET @CIPHERTEXT = ENCRYPTBYCERT(CERT_ID('SOURCE_CERT'), @CLEARTEXT);  
SET @UNCIPHEREDTEXT_Source =   
    DECRYPTBYCERT(CERT_ID('SOURCE_CERT'), @CIPHERTEXT)  
-- Encryption and decryption result in SOURCE_DB  
SELECT @CLEARTEXT AS SourceClearText, @CIPHERTEXT AS SourceCipherText,   
       @UNCIPHEREDTEXT_Source AS SourceDecryptedText;  
  
-- SWITCH DATABASE  
USE TARGET_DB;  
  
DECLARE @UNCIPHEREDTEXT_Target nvarchar(100);  
SET @UNCIPHEREDTEXT_Target = DECRYPTBYCERT(CERT_ID('TARGET_CERT'), @CIPHERTEXT);  
-- Encryption and decryption result in TARGET_DB  
SELECT @CLEARTEXT AS ClearTextInTarget, @CIPHERTEXT AS CipherTextInTarget, @UNCIPHEREDTEXT_Target AS DecriptedTextInTarget;   
GO

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