(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.

Note: This example requires Chilkat v11.0.0 or greater.

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
    DECLARE @iTmp0 int
    -- Important: Do not use nvarchar(max).  See the warning about using nvarchar(max).
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    -- 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.Rsa', @rsa OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    -- 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, 'qa_data/rsaKeys/test.snk'
    EXEC sp_OAGetProperty @rsa, 'LastMethodSuccess', @iTmp0 OUT
    IF @iTmp0 = 0
      BEGIN
        EXEC sp_OAGetProperty @rsa, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @rsa
        RETURN
      END

    DECLARE @pubKey int
    EXEC @hr = sp_OACreate 'Chilkat.PublicKey', @pubKey OUT

    EXEC sp_OAMethod @pubKey, 'LoadFromString', @success OUT, @xmlKey
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @pubKey, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @rsa
        EXEC @hr = sp_OADestroy @pubKey
        RETURN
      END
    EXEC sp_OAMethod @rsa, 'UsePublicKey', @success OUT, @pubKey

    -- Our message data will be encrypted using 128-bit AES
    -- encryption, using CBC (cipher-block chaining).
    DECLARE @crypt int
    EXEC @hr = sp_OACreate 'Chilkat.Crypt2', @crypt OUT

    EXEC sp_OASetProperty @crypt, 'CryptAlgorithm', 'aes'
    EXEC sp_OASetProperty @crypt, 'CipherMode', 'cbc'
    EXEC sp_OASetProperty @crypt, 'KeyLength', 128

    -- Generate 128-bit (16 bytes) secret key and return as a hex string.
    EXEC sp_OASetProperty @crypt, 'EncodingMode', 'hex'
    DECLARE @secretKey nvarchar(4000)
    EXEC sp_OAMethod @crypt, 'GenRandomBytesENC', @secretKey OUT, 16

    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:
    DECLARE @privKey int
    EXEC @hr = sp_OACreate 'Chilkat.PrivateKey', @privKey OUT

    EXEC sp_OAMethod @privKey, 'LoadXml', @success OUT, @xmlKey
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @privKey, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @rsa
        EXEC @hr = sp_OADestroy @pubKey
        EXEC @hr = sp_OADestroy @crypt
        EXEC @hr = sp_OADestroy @privKey
        RETURN
      END
    EXEC sp_OAMethod @rsa, 'UsePrivateKey', @success OUT, @privKey

    -- 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.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 @pubKey
    EXEC @hr = sp_OADestroy @crypt
    EXEC @hr = sp_OADestroy @privKey
    EXEC @hr = sp_OADestroy @crypt2


END
GO