• SQL Server Security

    SQL Server 2012 Best Practices Analyzer

    • 0 Comments

    Copied from an internal email from a PM on the team, Jakub -

    I’m pleased to announce that SQL Server 2012 Best Practices Analyzer (BPA) has been released and is available for download at http://www.microsoft.com/download/en/details.aspx?id=29302.

    Customer Value

    The Microsoft SQL Server 2012 BPA is a diagnostic tool that
    performs the following functions:


    • Gathers information about a Server and a
      Microsoft SQL Server 2012 instance installed on that Server.

    • Determines if the configurations are set
      according to the recommended best practices.

    • Reports on all configurations, indicating
      settings that differ from recommendations.

    • Indicates potential problems in the installed
      instance of SQL Server.

    • Recommends solutions to potential problems.

     

  • SQL Server Security

    Security Best Practice and Label Security Whitepapers

    • 4 Comments

    2 New Whitepapers:

  • SQL Server Security

    Azure Trust Services

    • 0 Comments

    Microsoft is working on a new Windows Azure service through SQL Azure Labs, called Trust Services. It is an application-level encryption framework that can be used to protect sensitive data stored on the Windows Azure Platform. By using Trust Services you can store keys, authorizations and encryption policies in the cloud, and use them to encrypt and decrypt sensitive data.

    Trust Services provides a API that simplifies the development process and enables easy integration with data driven applications.

    Check it out at Microsoft Codename "Trust Services". We are looking forward for your feedback.

  • SQL Server Security

    SQL Azure Security Services

    • 0 Comments

    Last week, we released SQL Azure Security Services through SQL Azure Labs. In this initial version of our labs, you can

    • Scan your SQL Azure server or individual databases for security issues - We look for design issues, elevation issues and etc.

    • Get a report of your database security model - You can quickly know which users exist in a database, role memberships, permissions on various objects and etc, to reason over presence of user accounts or permissions on various objects.

    • Scan your data for malware presence (Currently we only check for Mass SQL Injection Attacks) - We have been observing Automated Mass SQL Injection attacks for over 4 years now, we scan for presence of malicious javascript in your data.

    Please try the service here and let us know your feedback.

    - Bala Neerumalla.

     

  • SQL Server Security

    Meet the team at SQL PASS Summit 2011

    • 0 Comments

    PASS Summit 2011 is coming to Seattle this week starting October 11th 2011. You'll have the opportunity to meet a lot of folks from the SQL Server team during the event, and a variety of speakers that will share their experiences and delight you with awesome SQL Server sessions.

    Lastly, the SQL Server Engine Security  Team will be present at the conference and this is your opportunity to meet with us so that we can answer your questions. For those interested in SQL Server Security, we recommend that you attend the following talks –

    (1)   SQL PASS Session - [DBA-412-M] What’s New in Security for SQL Server Code Name "Denali"

    Friday, October 14, 2011 2:00 PM-3:15 PM, Room 608

    Presented by Il-Sung Lee

     

    (2) SQL PASS Theater Session - SQL Server 2011 Audit Enhancements

    Wednesday, October 12, 2011, 10:30am - 11:00am, Microsoft Booth # 208

    Presented by Jack Richins

     

     

    (3) SQL PASS Theater Session – A quick lap around SQL Server Encryption

    Wednesday, October 12, 2011, 1:45pm – 2:15pm, Microsoft Booth # 208

    Presented by Don Pinto

     

    Also, don’t forget to stop by the Security and Compliance Booth and the Performance/Security Expert POD to meet with our team members, and ask questions or share your product feedback and suggestions.



    We look forward to seeing you at SQL PASS!

    - SQL Engine Security Team-

  • SQL Server Security

    Data Hashing in SQL Server

    • 3 Comments

    A common scenario in data warehousing applications is knowing what source system records to update, what data needs to be loaded and which data rows can be skipped as nothing has changed since they were last loaded. Another possible scenario is the need to facilitate searching data that is encrypted using cell level encryption or storing application passwords inside the database.

     Data Hashing can be used to solve this problem in SQL Server.

     A hash is a number that is generated by reading the contents of a document or message. Different messages should generate different hash values, but the same message causes the algorithm to generate the same hash value.

    The HashBytes function in SQL Server

    SQL Server has a built-in function called HashBytes to support data hashing.

     HashBytes ( '<algorithm>', { @input | 'input' } )
    <algorithm>::= MD2 | MD4 | MD5 | SHA | SHA1 | SHA2_256 | SHA2_512

     Here is a sample along with the return values commented in the next line :

     

     

    Properties of good hash functions

    A good hashing algorithm has these properties: 

    • It is especially sensitive to small changes in the input. Minor changes to the document will generate a very different hash result.
    • It is computationally unfeasible to reverse. There will be absolutely no way to determine what changed in the input or to learn anything about the content of an input by examining hash values. For this reason, hashing is often called one-way hashing.
    • It is very efficient.

     

    Should you encrypt or hash?

    During application development, it might be useful to understand when to encrypt your data vs. when to hash it.

    The difference is that encrypted data can be decrypted, while hashed data cannot be decrypted. Another key difference is that encryption normally results in different results for the same text but hashing always produces the same result for the same text. The deciding factor when choosing to encrypt or hash your data comes after you determine if you'll need to decrypt the data for offline processing.

    A typical example of data that needs to be decrypted would be within a payment processing system is a credit card number. Thus the credit card number should be encrypted in the payment processing system. However, in the case of security code for the credit card, hashing it is sufficient if only equality checks are done and the system does not need to know it’s real value.

    Encryption is a two way process but hashing is unidirectional

     

    How to use hashbytes for indexing encrypted data.

    Encryption introduces randomization and in there is no way to predict the outcome of an encryption built-in. Does that mean creating an index on top of encrypted data is not possible?

     However, data hashing can come to your rescue. Refer to this blog post to learn how.

     

    Which hash function should I choose?

    Although, most hashing functions are fast, the performance of a hashing function depends on the data to be hashed and the algorithm used.

     There is no magic bullet. For security purposes, it is advised to use the strongest hash function (SHA2_512). However, you can choose other hashing algorithms depending on your workload and data to hash.   

     

    Hash functions or CHECK_SUM()?

    SQL Server has the CHECK_SUM () (or BINARY_CHECKSUM ()) functions for generating the checksum value computed over a row of a table, or over a list of expressions.

    One problem with the CHECK_SUM() (or BINARY_CHECKSUM()) functions is that the probability of a collision may not be sufficiently low for all applications (i.e. it is possible to come across examples of two different inputs hashing to the same output value). Of course, collisions are possible with any functions that have a larger domain than its range but because the CHECK_SUM function implements a simple XOR, the probability of this collision is high.

    Try it out using the following example -

     

     ---

    Don Pinto, PM, SQL Server Engine

  • SQL Server Security

    Database Engine Permission Basics

    • 1 Comments

    I am posting this on behalf of my colleague Rick Byham, a technical writer on the SQL Server Team.

    Database Engine permissions are managed at the server level through logins and fixed server roles, and at the database level through database users and user-defined database roles.

    Logins

    Logins are individual user accounts for logging on to the SQL Server Database Engine. SQL Server supports logins based on Windows authentication and logins based on SQL Server authentication. For information about the two types of logins, see Choosing an Authentication Mode .

    Fixed Server Roles

    Fixed server roles are a set of preconfigured roles that provide convenient group of server-level permissions. Logins can be added to the roles using the sp_addsrvrolemember procedure.

    Database Users

    Logins are granted access to a database by creating a database user in a database and mapping that database user to login. Typically the database user name is the same as the login name, though it does not have to be the same. Each database user maps to a single login. A login can be mapped to only one user in a database, but can be mapped as a database user in several different databases.

    Fixed Database Roles

    Fixed database roles are a set of preconfigured roles that provide convenient group of database-level permissions. Database users and user-defined database roles can be added to the fixed database roles using the sp_addrolemember procedure.

    User-defined Database Roles

    Users with the CREATE ROLE permission can create new user-defined database roles to represent groups of users with common permissions. Typically permissions are granted or denied to the entire role, simplifying permissions management and monitoring.

    Typical Scenario

    The following example represents a common and recommended method of configuring permissions.

    In Active Directory:

    1. Create a Windows user for each person.
    2. Create Windows groups that represent the work units and the work functions.
    3. Add the Windows users to the Windows groups.

    In SQL Server:

    1. Create a login for the Windows groups. (If using SQL Server authentication, skip the Active Directory steps, and create SQL Server authentication logins here.)
    2. Create a database user for the login representing the Windows groups.
    3. Create one or more user-defined database roles, each representing a similar function. For example financial analyst, and sales analyst.
    4. Add database users to one or more user-defined database roles.
    5. Grant permissions to the user-defined database roles.

    Assigning Permissions

    Most permission statements have the format :

    AUTHORIZATION PERMISSION ON SECURABLE::NAME TO PRINCIPAL

    • AUTHORIZATION must be GRANT, REVOKE or DENY.
    • PERMISSION is listed in the chart referenced below.
    • ON SECURABLE::NAME is the server, server object, database, or database object and its name. Some permissions do not require ON SECURABLE::NAME because it is unambiguous or inappropriate in the context. For example the CREATE TABLE permission doesn’t require the ON SECURABLE::NAME clause.
    • PRINCIPAL is the login, user, or role which receives or loses the permission. Grant permissions to roles whenever possible.

    Sample grant statement: GRANT UPDATE ON OBJECT::Production.Parts TO PartsTeam

    Permissions are granted to security principals (logins, users, and roles) by using the GRANT statement. Permissions are explicitly denied by using the DENY command. A previously granted or denied permission is removed by using the REVOKE statement. Permissions are cumulative, with the user receiving all the permissions granted to the user, login, and any group memberships; however any permission denial overrides all grants.

    Tip: A common mistake is to attempt to remove a GRANT by using DENY instead of REVOKE. This can cause problems when a user receives permissions from multiple sources; which is quite common. The following example demonstrates the principal.

    The Sales group receives SELECT permissions on the OrderStatus table through the statement GRANT SELECT ON OBJECT::OrderStatus TO Sales. User Ted is a member of the Sales role. Ted has also been granted SELECT permission to the OrderStatus table under his own user name through the statement GRANT SELECT ON OBJECT::OrderStatus TO Ted. Presume the administer wishes to remove the GRANT to the Sales role.

    • If the administrator correctly executes REVOKE SELECT ON OBJECT::OrderStatus TO Sales, then Ted will retain SELECT access to the OrderStatus table through his individual GRANT statement.
    • If the administrator incorrectly executes DENY SELECT ON OBJECT::OrderStatus TO Sales then Ted, as a member of the Sales role, will be denied the SELECT permission because the DENY to Sales overrides his individual GRANT.

    Permission Hierarchy

    Permissions have a parent/child hierarchy. That is, if you grant SELECT permission on a database, if includes SELECT permission on all (child) schemas in the database. If you grant SELECT permission on a schema, it includes SELECT permission on all the (child) tables and views in the schema. The permissions are transitive; that is, if you grant SELECT permission on a database, it includes SELECT permission on all (child) schemas, and all (grandchild) tables, and all views.

    Permissions also have covering permissions. The CONTROL permission on an object, normally gives you all other permissions on the object.

    Because both the parent/child hierarchy and the covering hierarchy can act on the same permission, the permission system can get complicated. For example, let's take a table (Region), in a schema (Customers), in a database (SalesDB).

    • CONTROL permission on table Region includes all the other permissions on the table Region, including ALTER, SELECT, INSERT, UPDATE, DELETE, and some other permissions.
    • SELECT on the Customers schema that owns the Region table includes the SELECT permission on the Region table.

    So SELECT permission on the Region table can be achieved through any of these three statements:

    • GRANT SELECT ON OBJECT::Region TO Ted
    • GRANT CONTROL ON OBJECT::Region TO Ted
    • GRANT SELECT ON SCHEMA::Customers TO Ted
    • GRANT CONTROL ON SCHEMA::Customers TO Ted
    • GRANT SELECT ON DATABASE::SalesDB TO Ted
    • GRANT CONTROL ON DATABASE::SalesDB TO Ted

    Grant the Least Permissions

    The first permission listed above (GRANT SELECT ON OBJECT::Region TO Ted) is the most granular, that is, that statement is the least permission possible that grants the SELECT. No permissions to subordinate objects come with it. Always grant the least permission possible, but grant at higher levels in order to simplify the granting system. So if Ted needs permissions to the entire schema, grant SELECT once at the schema level, instead of granting SELECT at the table of view level many times. The design of the database has a great deal of impact on how successful this strategy can be. This strategy will work best when your database is designed so that objects needing identical permissions are included in a single schema.

    List of Permissions

    SQL Server 2008 R2 has 195 permissions. SQL Server Code-named 'Denali' has 214 permissions. The following graphic shows the permissions and their relationships to each other. Some of the higher level permissions (such as CONTROL SERVER) are listed many times.
    5710.Permissions_Poster_2008_R2_Wiki.pdf

    Permissions vs. Fixed Server and Fixed Database Roles

    The permissions of the fixed server roles and fixed database roles are similar but not exactly the same as the granular permissions. For example, members of the sysadmin fixed server role have all permissions on the instance of SQL Server, as do logins with the CONTROL SERVER permission. But granting the CONTROL SERVER permission does not make a login a member of the sysadmin fixed server role, and making adding a login to the sysadmin fixed server role does not explicitly grant the login the CONTROL SERVER permission. Sometimes a stored procedure will check permissions by checking the fixed role and not checking the granular permission. For example detaching a database requires membership in the db_owner fixed database role. The equivalent CONTROL DATABASE permission is not enough. These two systems operate in parallel but rarely interact with each other. Microsoft recommends using the newer, granular permission system instead of the fixed roles whenever possible.

    Monitoring permissions

    The following views return security information.

    • The logins and user-defined server roles (available in SQL Server Code-named 'Denali') on a server can be examined by using the sys.server_principals view.
    • The users and user-defined roles in a database can be examined by using the sys.database_principals view.
    • The permissions granted to logins and user-defined fixed server roles can be examined by using the sys.server_permissions view.
    • The permissions granted to user and user-defined fixed database roles can be examined by using the sys.database_permissions view.
    • Database role membership can be examined by using the sys. sys.database_role_members view.
    • Server role membership can be examined by using the sys. sys.server_role_members view.
    • For additional security related views, see Security Catalog Views (Transact-SQL) .

    The following statements return useful information about permissions.

    To return the explicit permissions granted or denied in a database, execute the following statement in the database.

    SELECT
    perms.state_desc AS State,
    permission_name AS [Permission],
    obj.name AS [on Object],
    dPrinc.name AS [to User Name],
    sPrinc.name AS [who is Login Name]
    FROM sys.database_permissions AS perms
    JOIN sys.database_principals AS dPrinc
    ON perms.grantee_principal_id = dPrinc.principal_id
    JOIN sys.objects AS obj
    ON perms.major_id = obj.object_id
    LEFT OUTER JOIN sys.server_principals AS sPrinc
    ON dPrinc.sid = sPrinc.sid

    To return the members of the server roles, execute the following statement.

    SELECT sRole.name AS [Server Role Name] , sPrinc.name AS [Members]
    FROM sys.server_role_members AS sRo
    JOIN sys.server_principals AS sPrinc
    ON sRo.member_principal_id = sPrinc.principal_id
    JOIN sys.server_principals AS sRole
    ON sRo.role_principal_id = sRole.principal_id;

    To return the members of the database roles, execute the following statement in the database.

    SELECT dRole.name AS [Database Role Name], dPrinc.name AS [Members]
    FROM sys.database_role_members AS dRo
    JOIN sys.database_principals AS dPrinc
    ON dRo.member_principal_id = dPrinc.principal_id
    JOIN sys.database_principals AS dRole
    ON dRo.role_principal_id = dRole.principal_id;

  • SQL Server Security

    SQL Server 2008 PCI DSS v.2.0 Whitepaper

    • 0 Comments

    If PCI compliance with SQL Server is a concern for you, then you'll probably want to check out the Deploying SQL Server 2008 R2 Based on Payment Card Industry Data Security Standards (PCI DSS) Version 2.0 white paper published by Parente Beard LLC. The paper is written by certified PCI auditors (QSAs) and is similar to the PCI v1.2 white paper that they previously published but updated for PCI DSS 2.0.  It should be an invaluable resource as you prepare for your certification.

    Il-Sung

  • SQL Server Security

    Integrity checks with EncryptByKey

    • 0 Comments

     

        This article is a follow up to “Prevent Tampering of Encrypted Data Using @add_authenticator Argument for ENCRYPTBYKEY”. In the last article we described a scenario where the security risk of copying encrypted data from one row to another could be blocked, but there are other scenarios that can benefit from using the @add_authenticator and @authenticator arguments of ENCRYPTBYKEY.

     

       Generally speaking, it is highly recommended to make use of the @add_authenticator  argument to add some form of integrity check, even if the value for the @authenticator parameter is a constant for the whole table. In order to understand the motivation for this recommendation, it is necessary to explain some basic concepts of block ciphers (The information I present in this article is a high-level abstraction of this subject).

     

        In cryptography there are several modes of operation to work with multiple blocks of data. One of the most common modes of operation is cipher-block chaining (CBC) mode, which has specific error propagation characteristics. In a nutshell, one error in a given block will affect only a deterministic number of blocks. The error-correction characteristics of this chaining mode may allow an adversary to tamper with the message. A common mitigation against such data tampering is to use an integrity check mechanism.

     

      The SQL Server ENCRYPTBYKEY built-in function uses CBC mode and therefore it is subject to this error-propagation mechanism and data tampering threat. Without using any integrity checks (i.e. if the default @add_authenticator is not set), an adversary may be able to manipulate the ciphertext in such a way that the blob can control some of the bits of the plaintext.  When the @add_authenticator  parameter is set, the @authenticator argument is used along with the @plaintext parameter to calculate a hash value that is encrypted and acts as the integrity check.

     

       Below is an example describing how a crafty adversary may tamper with data. For the following sample, we assume that the attacker has no direct access to the key (i.e. access to the key may be controlled via a stored procedure), but the attacker has direct write privileges (i.e. a way to insert the tampered ciphertext), and that other than verifying for null values, the application may not have any additional checks on decrypted data.

     

    CREATE TABLE t( data varbinary(200))

     

    INSERT INTO t VALUES (ENCRYPTBYKEY(key_guid('key1'), N'Testingtesting1234'));

    SELECT * FROM t;

    go

    -- 0x008CB602DBC9D145B899AC05FC14E2A30100000093384ECE68D1618EB5E197…

     

     

    -- Application “myApp” decryps data and returns the plaintext

    -- “Testingtesting1234”

    SELECT CONVERT( nvarchar(100), DECRYPTBYKEY(data)) FROM t

     

      Now, imagine that the attacker may be able to inject the following ciphertext (notice that the attacker modified a single bit of the original ciphertext):

     

    INSERT INTO t VALUES (

        0x008CB602DBC9D145B899AC05FC14E2A30100000093384ECE68D1618EB5F197…);

    SELECT * FROM t;

     

    Results:

    Testingtesting1234

    estingtesting1234

     

       Now let’s see what happens when using the @authenticator parameter. In this particular case I am using an arbitrary string to demonstrate the integrity check. The value for the @authenticator argument in this case is not important, as long as it is the same value for encryption and decryption calls.

     

    INSERT INTO t VALUES (

        ENCRYPTBYKEY(key_guid('key1'), N'Testingtesting1234', 1, 'abc'));

    SELECT * FROM t;

    -- 0x008CB602DBC9D145B899AC05FC14E2A3010000009925C3FB4D21B13D92869A53BB959303483575FE0D…

     

    -- Testingtesting1234

    SELECT CONVERT( nvarchar(100), DECRYPTBYKEY(data, 1, 'abc')) FROM t

     

    Attacker:

    INSERT INTO t VALUES (0x008CB602DBC9D145B899AC05FC14E2A3010000009925C3FB4D21B13D92869A53BB959303483575FF0D …)

     

    SELECT CONVERT( nvarchar(100), DECRYPTBYKEY(data, 1, 'abc')) FROM t

     

    Results:

    Testingtesting1234

    NULL

     

       As the final NULL result shows, the integrity check failed, and instead of returning a corrupted plaintext, the result of the decrypt call is discarded and the DECRYPTBYKEY function returns null.

     

      -Raul Garcia

     

    P.S. Thanks a lot to Jack Richins & Rick Byham for their feedback.

     

     

     

     

  • SQL Server Security

    Prevent Tampering of Encrypting Data Using add_authenticator Argument of EncryptByKey

    • 0 Comments

       This article is one of several articles discussing some of the best practices for encrypting data. This article demonstrates how the @add_authenticator argument of the ENCRYPTBYKEY function can help prevent tampering with encrypted data.

       Imagine the following scenario: The DBA is encrypting the salary column for all employees in such a way that people with authorization to access the table, but no access to the encryption key can see and manipulate the table, but cannot access the salary in plaintext. Mallory is one such employee, who has SELECT, INSERT & UPDATE on the table as required for her daily job, but no access to the encryption keys protecting the salary column.

    CREATE TABLE employees( employee_id int identity primary key, name nvarchar(256), salary_crypt varbinary(8000));

    go

    CREATE CERTIFICATE cert_demo WITH SUBJECT = 'Encryption demo';

    go

    CREATE SYMMETRIC KEY key_employee WITH ALGORITHM = AES_256

    ENCRYPTION BY CERTIFICATE cert_demo;

    go

    OPEN SYMMETRIC KEY key_employee DECRYPTION BY CERTIFICATE cert_demo;

    go

    INSERT INTO employees VALUES ( N'Alice',

    ENCRYPTBYKEY( key_guid('key_employee'),

    CONVERT(varbinary(100), 50000.00)));

    INSERT INTO employees VALUES ( N'Bob',

    ENCRYPTBYKEY( key_guid('key_employee'),

    CONVERT(varbinary(100), 1000.00)));

    INSERT INTO employees VALUES ( N'Mallory',

    ENCRYPTBYKEY( key_guid('key_employee'),

    CONVERT(varbinary(100), 1000.00)));

    go

     

    --1   Alice       5000

    --2   Bob         1000

    --3   Mallory     1000

    SELECT employee_id, name, CONVERT(decimal,

    DECRYPTBYKEY(salary_crypt)) AS salary FROM employees;

    go

     

    CLOSE SYMMETRIC KEY key_employee;

    Go

    CLOSE SYMMETRIC KEY key_employee;

    go

     

    CREATE USER [mallory] WITHOUT LOGIN;

    go

     

    GRANT UPDATE ON employees TO [mallory];

    go

    GRANT SELECT ON employees TO [mallory];

    go

     

      In this scenario, Mallory may not be able to recover the plaintext from anybody else in the company, but she may still be able to modify her own salary. She may not be able to see the salary for Alice, her manager, but she can easily guess that Alice’s salary is higher than her own. What would Mallory do? Simply copy Alice’s salary into her own row.

     

    EXECUTE AS USER = 'mallory';

    go

     

    --Msg 15151, Level 16, State 1, Line 1

    --Cannot find the symmetric key 'key_employee', because it does not exist or you do not have permission.

    OPEN SYMMETRIC KEY key_employee DECRYPTION BY CERTIFICATE cert_demo;

    go

     

    --1   Alice 0x... (Alice’s salary)

    --2   Bob 0x... (Bob’s salary)

    --3   Mallory 0x... (Mallory’s salary)

    SELECT * FROM employees;

    go

     

    -- Mallory can copy Alice’s salary into her own row

    -- Alice's ID = 1

    -- Mallory's ID = 3

    DECLARE @ceo_grade_salary varbinary(8000);

    SELECT @ceo_grade_salary = salary_crypt FROM employees WHERE employee_id = 1;

    UPDATE employees SET salary_crypt = @ceo_grade_salary WHERE employee_id = 3;

    go

     

    --1   Alice 0x... (Alice’s salary)

    --2   Bob 0x... (Bob’s salary)

    --3   Mallory 0x... (Alice’s salary)

    -- Looks like a successful attack at a glance…

    SELECT * FROM employees;

    go

     

    REVERT;

    go

     

      If the ciphertext for salary was created without any form of integrity check that takes into account the context in which the value is meaningful (i.e. it hasn’t been copied from one row to another), mallory’s attack may be successful.

    -- ... and it was indeed a successful attack!

    --

    --1   Alice       5000

    --2   Bob         1000

    --3   Mallory     5000

    SELECT employee_id, name, CONVERT(decimal,

    DECRYPTBYKEY(salary_crypt)) AS salary FROM employees;

    Go

     

      In order to prevent these kind of attacks using SQL Server encryption built-ins, the application developer may make use of the @add_authenticator parameter set to 1 and set the @authenticator parameter to a unique-per-row, immutable value such as the employee ID in this example (which also happens to be the primary key in this case).

    DROP TABLE employees;

    go

    CREATE TABLE employees( employee_id int identity primary key,

    name nvarchar(256), salary_crypt varbinary(8000));

    go

     

    OPEN SYMMETRIC KEY key_employee DECRYPTION BY CERTIFICATE cert_demo;

    go

     

    --   This time we will use the employee ID as

    -- @authenticator for the encryption field

    --   Given the simplicity of the nature of this demo, I will create the

    -- rows first (to populate the ID) and add the salaries later

    --

    INSERT INTO employees VALUES ( N'Alice', null);

    INSERT INTO employees VALUES ( N'Bob', null);

    INSERT INTO employees VALUES ( N'Mallory', null);

    go

     

    -- Update each salary using the employee_id as @authenticator

    UPDATE employees SET salary_crypt =

    ENCRYPTBYKEY( key_guid('key_employee'),

    CONVERT(varbinary(100), 5000.00),

    1, CONVERT(varbinary(8000), employee_id))

    WHERE employee_id = 1;

     

    UPDATE employees SET salary_crypt =

    ENCRYPTBYKEY( key_guid('key_employee'),

    CONVERT(varbinary(100), 1000.00),

    1, CONVERT(varbinary(8000), employee_id))

    WHERE employee_id = 2;

     

    UPDATE employees SET salary_crypt =

    ENCRYPTBYKEY( key_guid('key_employee'),

    CONVERT(varbinary(100), 1000.00),

    1, CONVERT(varbinary(8000), employee_id))

    WHERE employee_id = 3;

    go

     

    --1   Alice       5000

    --2   Bob         1000

    --3   Mallory     1000

    SELECT employee_id, name, CONVERT(decimal,

    DECRYPTBYKEY(salary_crypt, 1, CONVERT(varbinary(8000), employee_id))) AS salary FROM employees;

    go

     

    CLOSE SYMMETRIC KEY key_employee;

    go

     

    GRANT UPDATE ON employees TO [mallory];

    go

    GRANT SELECT ON employees TO [mallory];

    go

     

      When using the @add_authenticator = 1 parameter during encryption, the @athenticator value is going to be used along to the plaintext to generate a hash (SHA-1) that is going to be verified during decryption. If the value for @authenticator specified during the decryption call cannot generate a matching hash (or not specified at all) the decryption call will fail and return NULL.

    -- Assuming the same attack as before

    -- Did Mallory succeeded this time?

    OPEN SYMMETRIC KEY key_employee DECRYPTION BY CERTIFICATE cert_demo;

    Go

     

    -- ... no, she didn’t! She got a null salary this time,

    -- This result would be a good indication of tampering

    --

    --1   Alice       5000

    --2   Bob         1000

    --3   Mallory     null

    SELECT employee_id, name, CONVERT(decimal,

    DECRYPTBYKEY(salary_crypt, 1, CONVERT(varbinary(8000), employee_id)))

    AS salary FROM employees;

    go

     

      I hope this information helps.

      -Raul

      Special thanks to Jack Richins & Rick Byham for their feedback while writing this article.

     

Page 1 of 7 (61 items) 12345»