rbytes | Generates cryptographically secure random byte sequences

I'm writing a Zenity-based status monitor for GNU dd(1) in Python. Due to the constraints of the system I'm targeting, the wrapper must run on Python 2, and cannot pull in external libraries.

Among the requirements are for Zenity's "Cancel" button to terminate dd if it's not yet finished.

I must do the following without delay (i.e. triggered/driven/immediately); if multiple of the below conditions are met/triggered simultaneously, they are to be executed in the listed order:

• when Zenity exits, terminate dd
• when dd writes to its stderr, munge+forward that data to Zenity's stdin
• when dd exits, if its return code was not 0, terminate Zenity

However, the epoll object seems to only be triggering on dd's output; it never triggers on Zenity exiting, despite my registering EPOLLHUP on Zenity's stdin.

How should/can this be done? I understand that epoll is the only primitive that can be used to correctly trigger on dd's output (via EPOLLIN); I also understand that it is an unweildy primitive which may be unsuitable for triggering on Zenity's exiting. (If required, I can implement more logic into this file; doing so is infinitely preferable to pulling in any 3rd-party library, however small or "common". I reiterate that I understand that epoll is unwieldy to work with and may require a large amount of glue-logic.)

Alternatively: if epoll is not the correct primitive for monitoring a subprocess for its exit, then what is the correct way to monitor a subprocess for exit while monitoring a subprocess for output in a Python 2 compatible way?

(I do not inherently need multithreaded capabilities; to take all actions sequentially would be fully in-spec; though, if multithreaded programming would be absolutely necessary in this case in order to avoid a busy-loop, then so be it.)

Below is my full code so far.

Given an X509 certificate object of a person. (The object's type is sun.security.x509.X509CertImpl). This person signed a String with his private key. Given the signature that was made by this person, when he signed the above mentioned String object.

My task is to verify this signature, but have difficulties with it.

When I try to verify the signature with the below code:

i want to use multithreading for capturing and processing the IP packets.one thread will only capture and store the packets for say 2 seconds and after that send(using pipe) this chunk to another thread where necessary informations will be extracted. to capture ip packets, am using RAW sockets and recvfrom() but recvfrom() returns -1 for each loop iteration. I think socket is not capturing the packets but i could not find out the reason...any help?? here is the Code...