SQL Server

Exporting and Importing Accumulated Entropy

See more PRNG Examples

When a system starts, a good established source of entropy may be lacking. The Fortuna algorithm keeps 32 internal entropy pools. When AddEntropy is called, it is added to these internal pools. (The details of the Fortuna algorithm can be read elsewhere.)

This example demonstrates how the entropy that has accumulated within the internal pools can be exported (such as when an application exits) and then imported when an application starts. (It is the application's job to persist the exported entropy to a database, file, etc.)

Importing entropy helps ensure an application is beginning with an adequate source of entropy for random number generation.

SQL Server

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr 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.

    SELECT @success = 0

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

    -- Generate random data and periodically add entropy...
    EXEC sp_OAMethod @fortuna, 'GetEntropy', @sTmp0 OUT, 32, 'hex'
    EXEC sp_OAMethod @fortuna, 'AddEntropy', @success OUT, @sTmp0, 'hex'
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GetEntropy', @sTmp0 OUT, 16, 'hex'
    EXEC sp_OAMethod @fortuna, 'AddEntropy', @success OUT, @sTmp0, 'hex'
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GetEntropy', @sTmp0 OUT, 16, 'hex'
    EXEC sp_OAMethod @fortuna, 'AddEntropy', @success OUT, @sTmp0, 'hex'
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GetEntropy', @sTmp0 OUT, 16, 'hex'
    EXEC sp_OAMethod @fortuna, 'AddEntropy', @success OUT, @sTmp0, 'hex'
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0

    DECLARE @exportedEntropy nvarchar(4000)
    EXEC sp_OAMethod @fortuna, 'ExportEntropy', @exportedEntropy OUT
    -- The application would persist the exported entropy in some way,
    -- such as to a file, or to a database, etc.

    -- Create a new PRNG object and initialize the internal entropy pools
    -- with the previously exported entropy:
    DECLARE @fortuna2 int
    EXEC @hr = sp_OACreate 'Chilkat.Prng', @fortuna2 OUT

    EXEC sp_OAMethod @fortuna2, 'ImportEntropy', @success OUT, @exportedEntropy

    -- Generate more random data, continuing to add entropy as we go along..
    EXEC sp_OAMethod @fortuna2, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna2, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna2, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna2, 'GetEntropy', @sTmp0 OUT, 16, 'hex'
    EXEC sp_OAMethod @fortuna2, 'AddEntropy', @success OUT, @sTmp0, 'hex'
    EXEC sp_OAMethod @fortuna2, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna2, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna2, 'GenRandom', @sTmp0 OUT, 16, 'hex'
    PRINT @sTmp0
    EXEC sp_OAMethod @fortuna2, 'GetEntropy', @sTmp0 OUT, 16, 'hex'
    EXEC sp_OAMethod @fortuna2, 'AddEntropy', @success OUT, @sTmp0, 'hex'
    -- ..

    EXEC @hr = sp_OADestroy @fortuna
    EXEC @hr = sp_OADestroy @fortuna2


END
GO