PureBasic

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.

PureBasic

IncludeFile "CkPrng.pb"

Procedure ChilkatExample()

    success.i = 0

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

    success = 0

    fortuna.i = CkPrng::ckCreate()
    If fortuna.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Generate random data and periodically add entropy...
    success = CkPrng::ckAddEntropy(fortuna,CkPrng::ckGetEntropy(fortuna,32,"hex"),"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    success = CkPrng::ckAddEntropy(fortuna,CkPrng::ckGetEntropy(fortuna,16,"hex"),"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    success = CkPrng::ckAddEntropy(fortuna,CkPrng::ckGetEntropy(fortuna,16,"hex"),"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    success = CkPrng::ckAddEntropy(fortuna,CkPrng::ckGetEntropy(fortuna,16,"hex"),"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna,16,"hex")

    exportedEntropy.s = CkPrng::ckExportEntropy(fortuna)
    ; 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:
    fortuna2.i = CkPrng::ckCreate()
    If fortuna2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPrng::ckImportEntropy(fortuna2,exportedEntropy)

    ; Generate more random data, continuing to add entropy as we go along..
    Debug CkPrng::ckGenRandom(fortuna2,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna2,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna2,16,"hex")
    success = CkPrng::ckAddEntropy(fortuna2,CkPrng::ckGetEntropy(fortuna2,16,"hex"),"hex")
    Debug CkPrng::ckGenRandom(fortuna2,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna2,16,"hex")
    Debug CkPrng::ckGenRandom(fortuna2,16,"hex")
    success = CkPrng::ckAddEntropy(fortuna2,CkPrng::ckGetEntropy(fortuna2,16,"hex"),"hex")
    ; ..


    CkPrng::ckDispose(fortuna)
    CkPrng::ckDispose(fortuna2)


    ProcedureReturn
EndProcedure