(SQL Server) RSA Decrypt Binary

When something is RSA encrypted, the output is always equal in size to the RSA key. For example, if "Hello World" is encrypted with a 1024-bit RSA key, the output is 128 bytes (because 1024 bits / 8 bits per byte = 128 bytes). You can see that the size of the RSA key imposes a limit on how many bytes can be encrypted. Thus RSA encryption is for small amounts of data. A typical use for RSA encryption is to encrypt a bulk (symmetric) encryption key.

In this example, we have a binary file containing the result of RSA encryption. The size of the file tells us the RSA key size. For example, if the file is exactly 256 bytes, we know that the RSA key required to decrypt must be a 2048-bit key.

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)
    -- This example assumes the Chilkat API to have been previously unlocked.
    -- See Global Unlock Sample for sample code.

    DECLARE @rsa int
    -- Use "Chilkat_9_5_0.Rsa" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.Rsa', @rsa OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @privKey int
    -- Use "Chilkat_9_5_0.PrivateKey" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.PrivateKey', @privKey OUT

    DECLARE @success int
    EXEC sp_OAMethod @privKey, 'LoadPemFile', @success OUT, 'myPrivateKey.pem'
    IF @success <> 1
      BEGIN
        EXEC sp_OAGetProperty @privKey, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @rsa
        EXEC @hr = sp_OADestroy @privKey
        RETURN
      END

    EXEC sp_OAMethod @rsa, 'ImportPrivateKeyObj', @success OUT, @privKey
    IF @success <> 1
      BEGIN
        EXEC sp_OAGetProperty @rsa, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @rsa
        EXEC @hr = sp_OADestroy @privKey
        RETURN
      END

    -- Load the encrypted bytes.
    -- This will typically be a file that is 128, 256, etc. bytes in length.
    -- For example, maybe it is a file containing an encrypted passphrase...
    DECLARE @bdEncrypted int
    -- Use "Chilkat_9_5_0.BinData" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @bdEncrypted OUT

    EXEC sp_OAMethod @bdEncrypted, 'LoadFile', @success OUT, 'qa_data/passphrase.enc'
    IF @success <> 1
      BEGIN

        PRINT 'Failed to load file.'
        EXEC @hr = sp_OADestroy @rsa
        EXEC @hr = sp_OADestroy @privKey
        EXEC @hr = sp_OADestroy @bdEncrypted
        RETURN
      END

    -- In this case, we know that it was a string that was encrypted,
    -- so decryption should result in a string.
    -- To make things easy, we'll pass the RSA encrypted data as a Base64 string 
    -- to the decryptor.
    EXEC sp_OASetProperty @rsa, 'EncodingMode', 'base64'
    DECLARE @passphrase nvarchar(4000)
    EXEC sp_OAMethod @bdEncrypted, 'GetEncoded', @sTmp0 OUT, 'base64'
    EXEC sp_OAMethod @rsa, 'DecryptStringENC', @passphrase OUT, @sTmp0, 1
    EXEC sp_OAGetProperty @rsa, 'LastMethodSuccess', @iTmp0 OUT
    IF @iTmp0 <> 1
      BEGIN
        EXEC sp_OAGetProperty @rsa, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @rsa
        EXEC @hr = sp_OADestroy @privKey
        EXEC @hr = sp_OADestroy @bdEncrypted
        RETURN
      END


    PRINT 'Decrypted passphrase: ' + @passphrase

    EXEC @hr = sp_OADestroy @rsa
    EXEC @hr = sp_OADestroy @privKey
    EXEC @hr = sp_OADestroy @bdEncrypted


END
GO