March, 2009

   Since the introduction of SQL Server 2008 extensible key management  (EKM), new opportunities may arise to handle data encryption on the client while still making the plaintext data accessible to authorized users in SQL Server. One issue between SQL Server and third party clients has been already discussed in the SQL Server Security forum in the past: describing the cryptographic message elements used by the resulting ciphertext generated by EncryptByKey builtin.

  While we are in the process of finalizing our documentation regarding this subject matter, I would like to take this opportunity to bring you an early draft view of the information and to get your feedback.. Below I will explain each one of the parts of the message along with an example. Notice that in all cases we are using little-endian byte ordering.

CipherTextMessage := KeyGUID + EncryptionHeader + EncryptedMessage

KeyGUID := {16 bytes} Key_guid. This GUID serves as an identifier for the key and it is stored in metadata (SELECT key_guid FROM sys.symmetric_keys). It is used during decryption for finding the corresponding key in the keyring.

EncryptionHeader := Headerversion + ReservedBytes

Headerversion := {1 byte} SQL Server encryption message version. Current version = 1

ReservedBytes := {3 byte} Reserved. Must be 0.

EncryptedMessage := InitializationVector + _EncryptFunction(SymKey, InitializationVector, InnerMessage)

InitializationVector := {1 block} the length of this field depends on the algorithm being used. All AES family keys will be 16 bytes per block, while the DES family keys are 8 bytes per block. Initialization vectors are used to initialize the block algorithm. It is not intended to be a secret, but must be unique for every call to the encryption function in order to avoid revealing patterns. For simplicity we will refer to the Initialization Vector as IV.

_EncryptFunction(IV, key, plaintext) := {variable length} function used to encrypt the plaintext data using the key (the algorithm is specified by the key itself) and the IV. In the case of SQL Server, this function is the CryptEncrypt, but since the supported encryption algorithms are standard, this function should be considered generic.

  Interoperability note: We use the block cipher in Cipher Block Chaining (CBC) mode. (default mode for most algorithms for Microsoft cryptographic providers, see AES provider Algorithms in BOL for further details).

InnerMessage := InnerMessageHeader + IntegrityBytes + Plaintext

InnerMessageHeader := MagicNumber + IntegrityBytesLength + PlaintextLength

MagicNumber := {4 bytes} As the name suggests, it is only an arbitrary value used to identify the message format. The current expected value is 3131961357 (decimal, unsigned). The main goal of this value is to detect if the message format is the expected one (if the value is incorrect, the message will be discarded). Extra points for anyone who identified the hexadecimal representation for this value which is (DWORD) 0xBAADF00D. For anyone curious about magic numbers, here is an interesting article about hexspeak.

IntegrityBytesLength := {2 bytes} The length of the IntegrityBytes field. May be either 0 or 20 (decimal).

IntegrityBytes := {IntegrityBytesLength bytes} This field is used when the @authenticator parameter is used when calling EncryptByKey. When this parameter is used, the Integrity field will be the cryptographic hash (SHA1) of the @ClearText (Plaintext) concatenated with the @authenticator parameter.

PlaintextLength := {2 bytes} The length of the Plaintext field.

Plaintext := {PlaintextLength bytes} The content of the @ClearText parameter (binary representation) when calling EncryptByKey.

Let’s use concrete examples and analyze each part of the message. For example, a call to SELECT ENCRYPTBYKEY( key_guid('key1'), 'Hello World!') resulted in the following ciphertext:

0x0096F42B8789694F87002E54D30FA0210100000013BDD2DD73F4392654565D3D156A073D4E8B16E0E11D0984F8E564E986268BF7D5C21158F1A511347F0177C5B1B18D24

Detailed analysis of each field:

Since the rest of the message is encrypted, it would be of little value to try to analyze it in the current form, but the following analysis will describe the inner message before being encrypted:

0x0DF0ADBA00000C0048656C6C6F20576F726C6421

If we would have called the EncryptByKey builtin using the @authenticator parameter, the inner message would have looked slightly different; for example when calling SELECT ENCRYPTBYKEY( key_guid('key1'), 'Hello World!' ,1, 'SQL Server 2008 demo'):

0x0DF0ADBA14000C00429DF3A3B39257F69C3359CA7F94B3F26AF3BE2B48656C6C6F20576F726C6421

 -Raul Garcia
  SDE/T
  SQL Server Engine

I'm pretty sure that there are many of you who have to deal with regulatory compliance but how many of you are aware that we have a SQL Server Compliance web portal?  Check out http://www.microsoft.com/sqlserver/2008/en/us/compliance.aspx.  There's a lot of information listed there covering a variety of topics that are interesting to compliance situations.

While we're talking about compliance, if you're dealing with PCI DSS compliance, you may want to check out this webcast which is scheduled for the end of the month: SQL Server 2008 Capabilities for Meeting PCI Compliance Needs

Il-Sung Lee
Program Manager
SQL Server Engine Security

We would like your feedback on the scenarios where you need to assign default schemas to Windows groups. We have a post in the forums, but there has only been one reply so far. Please, if you have an opinion or even just want to express your support of us doing anything about this, head over and leave a comment.