(SQL Server) RSA Encrypting Symmetric Secret Key

The RSA encryption algorithm is computationally expensive. It is not the best choice for encrypting large amounts of data. Symmetric encryption algorithms such as AES (i.e. Rijndael) or Blowfish are much more efficient. A typical application scenario is that you want to send encrypted messages to a partner, but you don't want to send the symmetric key unprotected. A solution is to generate a public/private RSA key pair and provide your partner with the public key (in advance). You may then encrypt the symmetric algorithm's key using the RSA private key. Next, encrypt the message using the symmetric algorithm, and send your partner both the encrypted key and encrypted message. Your partner decrypts by first RSA decrypting the key, and then uses the decrypted symmetric key to decrypt the message content.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

// Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
//
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    -- This example assumes the Chilkat API to have been previously unlocked.
    -- See Global Unlock Sample for sample code.

    DECLARE @rsa int
    EXEC @hr = sp_OACreate 'Chilkat_9_5_0.Rsa', @rsa OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @crypt int
    EXEC @hr = sp_OACreate 'Chilkat_9_5_0.Crypt2', @crypt OUT

    -- Load a public/private key pair from a .snk key file.
    -- Assume you have already provided your partner with 
    -- the public key part of the key pair.
    DECLARE @xmlKey nvarchar(4000)
    EXEC sp_OAMethod @rsa, 'SnkToXml', @xmlKey OUT, 'chilkat2.snk'

    -- Alternatively, you may generate a public/private key pair 
    -- by calling GenerateKey..

    -- Import the private key into the RSA instance.
    DECLARE @success int
    EXEC sp_OAMethod @rsa, 'ImportPrivateKey', @success OUT, @xmlKey

    -- Our message data will be encrypted using 128-bit AES
    -- encryption, using CBC (cipher-block chaining).
    EXEC sp_OASetProperty @crypt, 'CryptAlgorithm', 'aes'
    EXEC sp_OASetProperty @crypt, 'CipherMode', 'cbc'
    EXEC sp_OASetProperty @crypt, 'KeyLength', 128

    -- Generate a 128-bit secret key from a passphrase and return it as a hex string.
    DECLARE @secretKey nvarchar(4000)
    EXEC sp_OAMethod @crypt, 'GenEncodedSecretKey', @secretKey OUT, 'secret', 'hex'

    PRINT 'Unencrypted Key: ' + @secretKey

    -- Use the key we generated:
    EXEC sp_OAMethod @crypt, 'SetEncodedKey', NULL, @secretKey, 'hex'

    -- RSA encrypt the secret key and return as a hex string:
    EXEC sp_OASetProperty @rsa, 'EncodingMode', 'hex'
    DECLARE @bUsePrivateKey int
    SELECT @bUsePrivateKey = 0
    DECLARE @encryptedKey nvarchar(4000)
    EXEC sp_OAMethod @rsa, 'EncryptStringENC', @encryptedKey OUT, @secretKey, @bUsePrivateKey

    -- Symmetric encrypt a message.  For this example the message
    -- is very short, but typically this is where a large amount
    -- of data may be encrypted.
    EXEC sp_OASetProperty @crypt, 'EncodingMode', 'base64'
    DECLARE @encryptedText nvarchar(4000)
    EXEC sp_OAMethod @crypt, 'EncryptStringENC', @encryptedText OUT, 'Hello World!'

    -- Show our encrypted key and encrypted text:

    PRINT 'Encrypted Key: ' + @encryptedKey

    PRINT 'Encrypted Text: ' + @encryptedText

    -- Assume we sent these strings to our partner...

    -- Here's what we do at the partner end:
    EXEC sp_OAMethod @rsa, 'ImportPublicKey', @success OUT, @xmlKey

    -- First, decrypt the encryptedKey:
    SELECT @bUsePrivateKey = 1
    DECLARE @decryptedKey nvarchar(4000)
    EXEC sp_OAMethod @rsa, 'DecryptStringENC', @decryptedKey OUT, @encryptedKey, @bUsePrivateKey

    PRINT 'Decrypted Key: ' + @decryptedKey

    -- Set our crypt object's properties and secret key:
    DECLARE @crypt2 int
    EXEC @hr = sp_OACreate 'Chilkat_9_5_0.Crypt2', @crypt2 OUT

    EXEC sp_OASetProperty @crypt2, 'CryptAlgorithm', 'aes'
    EXEC sp_OASetProperty @crypt2, 'CipherMode', 'cbc'
    EXEC sp_OASetProperty @crypt2, 'KeyLength', 128
    EXEC sp_OASetProperty @crypt2, 'EncodingMode', 'base64'
    EXEC sp_OAMethod @crypt2, 'SetEncodedKey', NULL, @decryptedKey, 'hex'

    -- Decrypt the message:
    DECLARE @decryptedText nvarchar(4000)
    EXEC sp_OAMethod @crypt2, 'DecryptStringENC', @decryptedText OUT, @encryptedText

    PRINT 'Decrypted Text: ' + @decryptedText

    EXEC @hr = sp_OADestroy @rsa
    EXEC @hr = sp_OADestroy @crypt
    EXEC @hr = sp_OADestroy @crypt2


END
GO