(DataFlex) 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

Use ChilkatAx-win32.pkg

Procedure Test
    Handle hoRsa
    Variant vPrivKey
    Handle hoPrivKey
    Boolean iSuccess
    Handle hoBdEncrypted
    String sPassphrase
    String sTemp1
    Boolean bTemp1

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

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

    Get Create (RefClass(cComChilkatPrivateKey)) To hoPrivKey
    If (Not(IsComObjectCreated(hoPrivKey))) Begin
        Send CreateComObject of hoPrivKey
    End

    Get ComLoadPemFile Of hoPrivKey "myPrivateKey.pem" To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoPrivKey To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get pvComObject of hoPrivKey to vPrivKey
    Get ComImportPrivateKeyObj Of hoRsa vPrivKey To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoRsa To sTemp1
        Showln sTemp1
        Procedure_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...
    Get Create (RefClass(cComChilkatBinData)) To hoBdEncrypted
    If (Not(IsComObjectCreated(hoBdEncrypted))) Begin
        Send CreateComObject of hoBdEncrypted
    End
    Get ComLoadFile Of hoBdEncrypted "qa_data/passphrase.enc" To iSuccess
    If (iSuccess <> True) Begin
        Showln "Failed to load file."
        Procedure_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.
    Set ComEncodingMode Of hoRsa To "base64"
    Get ComGetEncoded Of hoBdEncrypted "base64" To sTemp1
    Get ComDecryptStringENC Of hoRsa sTemp1 True To sPassphrase
    Get ComLastMethodSuccess Of hoRsa To bTemp1
    If (bTemp1 <> True) Begin
        Get ComLastErrorText Of hoRsa To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Decrypted passphrase: " sPassphrase


End_Procedure