DataFlex

DSA Signature Create and Verify

See more DSA Examples

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoCrypt
    String sHashStr
    Handle hoDsa
    String sPemPrivateKey
    String sHexSig
2    Handle hoDsa2
    String sPemPublicKey
    String sTemp1

    Move False To iSuccess

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

    Get Create (RefClass(cComChilkatCrypt2)) To hoCrypt
    If (Not(IsComObjectCreated(hoCrypt))) Begin
        Send CreateComObject of hoCrypt
    End

    Set ComEncodingMode Of hoCrypt To "hex"
    Set ComHashAlgorithm Of hoCrypt To "sha-1"

    // Return the SHA-1 hash of a file.  The file may be any size.
    // The Chilkat Crypt component will stream the file when 
    // computing the hash, keeping the memory usage constant
    // and reasonable.
    // The 20-byte SHA-1 hash is returned as a hex-encoded string.
    Get ComHashFileENC Of hoCrypt "hamlet.xml" To sHashStr

    Get Create (RefClass(cComChilkatDsa)) To hoDsa
    If (Not(IsComObjectCreated(hoDsa))) Begin
        Send CreateComObject of hoDsa
    End

    // Load a DSA private key from a PEM file.  Chilkat DSA
    // provides the ability to load and save DSA public and private
    // keys from encrypted or non-encrypted PEM or DER.
    // The LoadText method is for convenience only.  You may
    // use any means to load the contents of a PEM file into
    // a string.

    Get ComLoadText Of hoDsa "dsa_priv.pem" To sPemPrivateKey
    Get ComFromPem Of hoDsa sPemPrivateKey To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // You may optionally verify the key to ensure that it is a valid
    // DSA key.
    Get ComVerifyKey Of hoDsa To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Load the hash to be signed into the DSA object:
    Get ComSetEncodedHash Of hoDsa "hex" sHashStr To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Now that the DSA object contains both the private key and hash,
    // it is ready to create the signature:
    Get ComSignHash Of hoDsa To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // If SignHash is successful, the DSA object contains the
    // signature.  It may be accessed as a hex or base64 encoded
    // string.  (It is also possible to access directly in byte array form via
    // the "Signature" property.)
    Get ComGetEncodedSignature Of hoDsa "hex" To sHexSig
    Showln "Signature:"
    Showln sHexSig

    // -----------------------------------------------------------
    // Step 2: Verify the DSA Signature
    // -----------------------------------------------------------

    Get Create (RefClass(cComChilkatDsa)) To hoDsa2
    If (Not(IsComObjectCreated(hoDsa2))) Begin
        Send CreateComObject of hoDsa2
    End

    // Load the DSA public key to be used for verification:

    Get ComLoadText Of hoDsa2 "dsa_pub.pem" To sPemPublicKey
    Get ComFromPublicPem Of hoDsa2 sPemPublicKey To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Load the hash to be verified against the signature.
    Get ComSetEncodedHash Of hoDsa2 "hex" sHashStr To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Load the signature:
    Get ComSetEncodedSignature Of hoDsa2 "hex" sHexSig To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Verify:
    Get ComVerify Of hoDsa2 To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoDsa2 To sTemp1
        Showln sTemp1
    End
    Else Begin
        Showln "DSA Signature Verified!"
    End



End_Procedure