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Quiz based on Digital Principles and Computer Organization

1) Base of hexadecimal number system? Answer : 16 2) Universal gate in digital logic? Answer : NAND 3) Memory type that is non-volatile? Answer : ROM 4) Basic building block of digital circuits? Answer : Gate 5) Device used for data storage in sequential circuits? Answer : Flip-flop 6) Architecture with shared memory for instructions and data? Answer : von Neumann 7) The smallest unit of data in computing? Answer : Bit 8) Unit that performs arithmetic operations in a CPU? Answer : ALU 9) Memory faster than main memory but smaller in size? Answer : Cache 10) System cycle that includes fetch, decode, and execute? Answer : Instruction 11) Type of circuit where output depends on present input only? Answer : Combinational 12) The binary equivalent of decimal 10? Answer : 1010 13) Memory used for high-speed temporary storage in a CPU? Answer : Register 14) Method of representing negative numbers in binary? Answer : Two's complement 15) Gate that inverts its input signal? Answer : NOT 16)...

Fire walling to protect systems and networks

Fire walling to Protect Systems and Networks
* Firewalls are devices (or sometimes software) that sits on the border between two securities domains and monitor/log activity between them, sometimes avoiding the traffic that can pass between them based on certain criteria.
* For example a firewall router may permit HTTP: requests to pass through to a web server inside a company domain while not allowing telnet, ssh, or other traffic to pass through.
* A common architecture is to place a de-militarized zone, DMZ, which arrange of sits "between" the company domain and the outside world, as shown below. Company computers can extend either the DMZ or the outside world, but outside computers can only extend the DMZ. Perhaps most importantly, the DMZ cannot extend any of the other company computers, so even if the DMZ is breached, the attacker cannot get to the balance of the company network. (In some cases the DMZ may have restricted access to company computers, such as a web server on the DMZ that reqires to query a database on one of the other company computers.)
     figure: Domain separation via firewall.
* Firewalls themselves required to be resistant to attacks, and unfortunately have several vulnerabilities:
o Tunneling, which includes encapsulating forbidden traffic inside of packets that 
are allowed?
o Denial of service affects addressed at the firewall itself.
o Spoofing, in which an illegal host sends packets to the firewall with the 
return address of an authorized host.
* In extra to the normal firewalls protecting a company internal network from the outside world, there are also some specialized forms of firewalls that have been recently developed:
o A personal firewall is a software layer that guards an individual computer. It may be a part of the operating system or a unique software package.
o An application proxy firewall understands the protocols of a specific service and acts as a stand-in (and relay) for the particular service. For example, and SMTP proxy firewall would take SMTP requests from the outside world, examine them for security concerns, and forward only the "safe" ones on to the real SMTP server behind the firewall.
o XML firewalls examined XML packets only, and reject ill-formed packets. Similar 
firewalls exist for other specific protocols.
o System call firewalls protects the boundary between user mode and system mode, and delete any system calls that infringe security policies.

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