Creating and managing keys is an important part of the cryptographic process. Symmetric algorithms require the creation of a key and an initialization vector (IV). The key must be kept secret from anyone who should not decrypt your data. The IV does not have to be secret, but should be changed for each session. Asymmetric algorithms require the creation of a public key and a private key. The public key can be made public to anyone, while the private key must known only by the party who will decrypt the data encrypted with the public key. This section describes how to generate and manage keys for both symmetric and asymmetric algorithms.

Nov 20, 2014 Asymmetric encryption also takes readable data, scrambles it, and unscrambles it again at the other end, but there’s a twist: a different key is used for each end. Encrypters use a public key to scramble the data, and decrypters use the matching private (secret) key on the other end to unscramble it again. You can use this to acquire a byte array of the appropriate length (e.g. 32 bytes for AES256), which can be used as a key. Be sure to pass in the raw bytes, and not, e.g., a hex-encoded string. Alternatively, you may want to derive a key from some other source. A Key Derivation Function (KDF) is a function that transforms some input into a key. Generating Symmetric Private Key In C# and.NET. Major symmetric algorithms are AES, DES, RC2, Rijndael, and TripleDES. The GenerateKey and GenerateIV methods return the private secret key and initialization vector. Asymmetric cryptography, also known as public-key cryptography, is a process that uses a pair of related keys- one public key and one private key - to encrypt and decrypt a message and protect. Then we need to find a new value of e such that m=c^(ed) mod n. This is achieved by solving ed=kx phi(n) +1, where phi(n) is the Eulers Totient function. The reason to change the private key is if we believe that the keys have been compromised so we need a new key, but we need to keep the old public key.

Symmetric Keys

The symmetric encryption classes supplied by the .NET Framework require a key and a new initialization vector (IV) to encrypt and decrypt data. Whenever you create a new instance of one of the managed symmetric cryptographic classes using the parameterless constructor, a new key and IV are automatically created. Anyone that you allow to decrypt your data must possess the same key and IV and use the same algorithm. Generally, a new key and IV should be created for every session, and neither the key nor IV should be stored for use in a later session.

To communicate a symmetric key and IV to a remote party, you would usually encrypt the symmetric key by using asymmetric encryption. Sending the key across an insecure network without encrypting it is unsafe, because anyone who intercepts the key and IV can then decrypt your data. For more information about exchanging data by using encryption, see Creating a Cryptographic Scheme.

The following example shows the creation of a new instance of the TripleDESCryptoServiceProvider class that implements the TripleDES algorithm.

When the previous code is executed, a new key and IV are generated and placed in the Key and IV properties, respectively.

Sometimes you might need to generate multiple keys. In this situation, you can create a new instance of a class that implements a symmetric algorithm and then create a new key and IV by calling the GenerateKey and GenerateIV methods. The following code example illustrates how to create new keys and IVs after a new instance of the symmetric cryptographic class has been made.

When the previous code is executed, a key and IV are generated when the new instance of TripleDESCryptoServiceProvider is made. Another key and IV are created when the GenerateKey and GenerateIV methods are called.

Asymmetric Keys

The .NET Framework provides the RSACryptoServiceProvider and DSACryptoServiceProvider classes for asymmetric encryption. These classes create a public/private key pair when you use the parameterless constructor to create a new instance. Asymmetric keys can be either stored for use in multiple sessions or generated for one session only. While the public key can be made generally available, the private key should be closely guarded.

A public/private key pair is generated whenever a new instance of an asymmetric algorithm class is created. After a new instance of the class is created, the key information can be extracted using one of two methods:

• The ToXmlString method, which returns an XML representation of the key information.

• The ExportParameters method, which returns an RSAParameters structure that holds the key information.

Both methods accept a Boolean value that indicates whether to return only the public key information or to return both the public-key and the private-key information. An RSACryptoServiceProvider class can be initialized to the value of an RSAParameters structure by using the ImportParameters method.

Asymmetric private keys should never be stored verbatim or in plain text on the local computer. If you need to store a private key, you should use a key container. For more on how to store a private key in a key container, see How to: Store Asymmetric Keys in a Key Container.

The following code example creates a new instance of the RSACryptoServiceProvider class, creating a public/private key pair, and saves the public key information to an RSAParameters structure.

See also

APPLIES TO: SQL Server Azure SQL Database Azure Synapse Analytics (SQL DW) Parallel Data Warehouse

This topic describes how to create identical symmetric keys on two different servers in SQL Server 2019 (15.x) by using Transact-SQL. In order to decrypt ciphertext, you need the key that was used to encrypt it. When both encryption and decryption occur in a single database, the key is stored in the database and it is available, depending on permissions, for both encryption and decryption. But when encryption and decryption occur in separate databases or on separate servers, the key stored in one database is not available for use on the second database.

Before You Begin

Limitations and Restrictions

• When a symmetric key is created, the symmetric key must be encrypted by using at least one of the following: certificate, password, symmetric key, asymmetric key, or PROVIDER. The key can have more than one encryption of each type. In other words, a single symmetric key can be encrypted by using multiple certificates, passwords, symmetric keys, and asymmetric keys at the same time.

• When a symmetric key is encrypted with a password instead of the public key of the database master key, the TRIPLE DES encryption algorithm is used. Because of this, keys that are created with a strong encryption algorithm, such as AES, are themselves secured by a weaker algorithm.

Security

Permissions

Requires ALTER ANY SYMMETRIC KEY permission on the database. /key-generator-photoshop-cc-2014-mac.html. If AUTHORIZATION is specified, requires IMPERSONATE permission on the database user or ALTER permission on the application role. If encryption is by certificate or asymmetric key, requires VIEW DEFINITION permission on the certificate or asymmetric key. Only Windows logins, SQL Server logins, and application roles can own symmetric keys. Groups and roles cannot own symmetric keys.

Using Transact-SQL

To create identical symmetric keys on two different servers

1. In Object Explorer, connect to an instance of Database Engine.

2. On the Standard bar, click New Query.

3. Create a key by running the following CREATE MASTER KEY, CREATE CERTIFICATE, and CREATE SYMMETRIC KEY statements.

4. Connect to a separate server instance, open a different Query Window, and run the SQL statements above to create the same key on the second server.

5. Test the keys by first running the OPEN SYMMETRIC KEY statement and the SELECT statement below on the first server.

6. On the second server, paste the result of the previous SELECT statement into the following code as the value of @blob and run the following code to verify that the duplicate key can decrypt the ciphertext.

7. Close the symmetric key on both servers.

Encryption changes in SQL Server 2017 CU2

SQL Server 2016 uses the SHA1 hashing algorithm for its encryption work. Starting in SQL Server 2017, SHA2 is used instead. This means extra steps might be necessary to have your SQL Server 2017 installation decrypt items that were encrypted by SQL Server 2016. Here are the extra steps:

• Ensure your SQL Server 2017 is updated to at least Cumulative Update 2 (CU2).
  • See Cumulative Update 2 (CU2) for SQL Server 2017 for important details.
• After you install CU2, turn on trace flag 4631 in SQL Server 2017: DBCC TRACEON(4631, -1);
  • Trace flag 4631 is new in SQL Server 2017. Trace flag 4631 needs to be ON globally before you create the master key, certificate, or symmetrical key in SQL Server 2017. This enables these created items to interoperate with SQL Server 2016 and earlier versions.

For more guidance, see:

• Identical symmetric keys do not work between SQL Server 2017 and other SQL Server version

Asymmetric Function That Generates A New And Separate Key Every Time It Runs

For more information