DataFlex

Verify the RSA Signature of a SHA256 Hash

See more RSA Examples

Demonstrates how to verify an RSA signature of a SHA256 hash. DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Variant vPubKey
    Handle hoPubKey
    Handle hoRsa
    Handle hoBdHash
    Handle hoBdSig
    String sEnc
    String sTemp1
    String sTemp2

    Move False To iSuccess

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

    // Let's say you have a file containing the 32-bytes of a SHA256 hash,
    // and a file that is an RSA signature of those 32 bytes.
    // Here's how you verify using the RSA public key found in a PEM.

    Get Create (RefClass(cComChilkatPublicKey)) To hoPubKey
    If (Not(IsComObjectCreated(hoPubKey))) Begin
        Send CreateComObject of hoPubKey
    End
    Get ComLoadFromFile Of hoPubKey "rsaPubKey.pem" To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoPubKey To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get Create (RefClass(cComChilkatRsa)) To hoRsa
    If (Not(IsComObjectCreated(hoRsa))) Begin
        Send CreateComObject of hoRsa
    End

    // Get the public key.
    Get pvComObject of hoPubKey to vPubKey
    Get ComUsePublicKey Of hoRsa vPubKey To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoRsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Get the 32-byte SHA256 hash.
    Get Create (RefClass(cComChilkatBinData)) To hoBdHash
    If (Not(IsComObjectCreated(hoBdHash))) Begin
        Send CreateComObject of hoBdHash
    End
    Get ComLoadFile Of hoBdHash "myHash.sha256" To iSuccess
    If (iSuccess = False) Begin
        Showln "Failed to load SHA256 hash."
        Procedure_Return
    End

    // Get the RSA signature to be validated.
    Get Create (RefClass(cComChilkatBinData)) To hoBdSig
    If (Not(IsComObjectCreated(hoBdSig))) Begin
        Send CreateComObject of hoBdSig
    End
    Get ComLoadFile Of hoBdSig "mySig.sig" To iSuccess
    If (iSuccess = False) Begin
        Showln "Failed to load RSA signature."
        Procedure_Return
    End

    // Verify the signature against the SHA256 hash.
    Move "base64" To sEnc
    Set ComEncodingMode Of hoRsa To sEnc
    Get ComGetEncoded Of hoBdHash sEnc To sTemp1
    Get ComGetEncoded Of hoBdSig sEnc To sTemp2
    Get ComVerifyHashENC Of hoRsa sTemp1 "sha256" sTemp2 To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoRsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Signature validated."


End_Procedure