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Executable Text
In hacking, a shellcode is a small piece of code used as the payload in the exploitation of a software vulnerability. It is called "shellcode" because it typically starts a command shell from which the attacker can control the compromised machine, but any piece of code that performs a similar task can be called shellcode. Because the function of a payload is not limited to merely spawning a shell, some have suggested that the name shellcode is insufficient. However, attempts at replacing the term have not gained wide acceptance. Shellcode is commonly written in machine code. When creating shellcode, it is generally desirable to make it both small and executable, which allows it to be used in as wide a variety of situations as possible. Writing good shellcode can be as much an art as it is a science. In assembly code, the same function can be performed in a multitude of ways and there is some variety in the lengths of opcodes that can be used for this purpose; good shellcode ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hacker (computer Security)
A security hacker is someone who explores methods for breaching defenses and exploiting weaknesses in a computer system or network. Hackers may be motivated by a multitude of reasons, such as profit, protest, information gathering, challenge, recreation, or evaluation of a system weaknesses to assist in formulating defenses against potential hackers. The subculture that has evolved around hackers is often referred to as the "computer underground". Longstanding controversy surrounds the meaning of the term "hacker." In this controversy, computer programmers reclaim the term ''hacker'', arguing that it refers simply to someone with an advanced understanding of computers and computer networks and that ''cracker'' is the more appropriate term for those who break into computers, whether computer criminals ( black hats) or computer security experts ( white hats). A 2014 article noted that "the black-hat meaning still prevails among the general public". History Birth of subcult ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drive-by Download
Drive-by download is of two types, each concerning the unintended download of computer software from the Internet: # Authorized drive-by downloads are downloads which a person has authorized but without understanding the consequences (e.g. downloads which install an unknown or counterfeit executable program In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instructions", as opposed to a data file ..., ActiveX component, or Java applet). # Unauthorized drive-by downloads are downloads which happen without a person's knowledge, often a computer virus, spyware, malware, or crimeware. Drive-by downloads may happen when visiting a website, opening an Email attachment, e-mail attachment or clicking a link, or clicking on a deceptive pop-up window: by clicking on the window in the mistaken belief that, for example, an error repor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Null Character
The null character (also null terminator) is a control character with the value zero. It is present in many character sets, including those defined by the Baudot and ITA2 codes, ISO/IEC 646 (or ASCII), the C0 control code, the Universal Coded Character Set (or Unicode), and EBCDIC. It is available in nearly all mainstream programming languages. It is often abbreviated as NUL (or NULL, though in some contexts that term is used for the null pointer). In 8-bit codes, it is known as a null byte. The original meaning of this character was like NOP—when sent to a printer or a terminal, it has no effect (some terminals, however, incorrectly display it as space). When electromechanical teleprinters were used as computer output devices, one or more null characters were sent at the end of each printed line to allow time for the mechanism to return to the first printing position on the next line. On punched tape, the character is represented with no holes at all, so a new unpunched ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NOP Slide
In computer security, a NOP slide, NOP sled or NOP ramp is a sequence of NOP (no-operation) instructions meant to "slide" the CPU's instruction execution flow to its final, desired destination whenever the program branches to a memory address anywhere on the slide. The technique sees common usage in software exploits, where it is used to direct program execution when a branch instruction target is not known precisely. Other notable applications include defensive programming strategies such as EMC-aware programming. While a NOP slide will function if it consists of a list of canonical NOP instructions, the presence of such code is suspicious and easy to automatically detect. For this reason, practical NOP slides are often composed of non-canonical NOP instructions (such as moving a register to itself or adding zero), or of instructions that affect program state only inconsequentially, which makes them much more difficult to identify. A NOP-sled is the oldest and most widely kn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NOP (code)
In computer science, a NOP, no-op, or NOOP (pronounced "no op"; short for no operation) is a machine language instruction and its assembly language mnemonic, programming language statement, or computer protocol command that does nothing. Machine language instructions Some computer instruction sets include an instruction whose explicit purpose is to not change the state of any of the programmer-accessible registers, status flags, or memory. It often takes a well-defined number of clock cycles to execute. In other instruction sets, there is no explicit NOP instruction, but the assembly language mnemonic NOP represents an instruction which acts as a NOP; e.g., on the SPARC, sethi 0, %g0. A NOP must not access memory, as that could cause a memory fault or page fault. A NOP is most commonly used for timing purposes, to force memory alignment, to prevent hazards, to occupy a branch delay slot, to render void an existing instruction such as a jump, as a target of an execute inst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IA-32
IA-32 (short for "Intel Architecture, 32-bit", commonly called i386) is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the 80386 microprocessor in 1985. IA-32 is the first incarnation of x86 that supports 32-bit computing; as a result, the "IA-32" term may be used as a metonym to refer to all x86 versions that support 32-bit computing. Within various programming language directives, IA-32 is still sometimes referred to as the "i386" architecture. In some other contexts, certain iterations of the IA-32 ISA are sometimes labelled i486, i586 and i686, referring to the instruction supersets offered by the 80486, the P5 and the P6 microarchitectures respectively. These updates offered numerous additions alongside the base IA-32 set including floating-point capabilities and the MMX extensions. Intel was historically the largest manufacturer of IA-32 processors, with the second biggest supplier having been AMD. During the 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Character Encodings In HTML
While Hypertext Markup Language (HTML) has been in use since 1991, HTML 4.0 from December 1997 was the first standardized version where international characters were given reasonably complete treatment. When an HTML document includes special characters outside the range of seven-bit ASCII, two goals are worth considering: the information's integrity, and universal browser display. Specifying the document's character encoding There are two general ways to specify which character encoding is used in the document. First, the web server can include the character encoding or "charset" in the Hypertext Transfer Protocol (HTTP) Content-Type header, which would typically look like this: Content-Type: text/html; charset=utf-8 This method gives the HTTP server a convenient way to alter document's encoding according to content negotiation; certain HTTP server software can do it, for example Apache with the module mod_charset_lite. Second, a declaration can be included within the docume ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Percent-encoding
Percent-encoding, also known as URL encoding, is a method to encode arbitrary data in a Uniform Resource Identifier (URI) using only the limited US-ASCII characters legal within a URI. Although it is known as ''URL encoding'', it is also used more generally within the main Uniform Resource Identifier (URI) set, which includes both Uniform Resource Locator (URL) and Uniform Resource Name (URN). As such, it is also used in the preparation of data of the application/x-www-form-urlencoded media type, as is often used in the submission of HTML form data in HTTP requests. Percent-encoding in a URI Types of URI characters The characters allowed in a URI are either ''reserved'' or ''unreserved'' (or a percent character as part of a percent-encoding). ''Reserved'' characters are those characters that sometimes have special meaning. For example, forward slash characters are used to separate different parts of a URL (or more generally, a URI). ''Unreserved'' characters have no such m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymorphic Code
In computing, polymorphic code is code that uses a polymorphic engine to mutate while keeping the original algorithm intact - that is, the ''code'' changes itself every time it runs, but the ''function'' of the code (its semantics) will not change at all. For example, the simple math expressions 3+1 and 6-2 both achieve the same result, yet run with different machine code in a CPU. This technique is sometimes used by computer viruses, shellcodes and computer worms to hide their presence. Encryption is the most common method to hide code. With encryption, the main body of the code (also called its payload) is encrypted and will appear meaningless. For the code to function as before, a decryption function is added to the code. When the code is ''executed'', this function reads the payload and decrypts it before executing it in turn. Encryption alone is not polymorphism. To gain polymorphic behavior, the encryptor/decryptor pair is mutated with each copy of the code. This allows di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intrusion Detection
An intrusion detection system (IDS; also intrusion prevention system or IPS) is a device or software application that monitors a network or systems for malicious activity or policy violations. Any intrusion activity or violation is typically reported either to an administrator or collected centrally using a security information and event management (SIEM) system. A SIEM system combines outputs from multiple sources and uses alarm filtering techniques to distinguish malicious activity from false alarms. IDS types range in scope from single computers to large networks. The most common classifications are network intrusion detection systems (NIDS) and host-based intrusion detection systems (HIDS). A system that monitors important operating system files is an example of an HIDS, while a system that analyzes incoming network traffic is an example of an NIDS. It is also possible to classify IDS by detection approach. The most well-known variants are signature-based detection (recogni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-modifying Code
In computer science, self-modifying code (SMC) is code that alters its own instructions while it is executing – usually to reduce the instruction path length and improve performance or simply to reduce otherwise repetitively similar code, thus simplifying maintenance. The term is usually only applied to code where the self-modification is intentional, not in situations where code accidentally modifies itself due to an error such as a buffer overflow. Self-modifying code can involve overwriting existing instructions or generating new code at run time and transferring control to that code. Self-modification can be used as an alternative to the method of "flag setting" and conditional program branching, used primarily to reduce the number of times a condition needs to be tested. The method is frequently used for conditionally invoking test/debugging code without requiring additional computational overhead for every input/output cycle. The modifications may be performed: * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alphanumeric Code
Alphanumericals or alphanumeric characters are a combination of alphabetical and numerical characters. More specifically, they are the collection of Latin letters and Arabic digits. An alphanumeric code is an identifier made of alphanumeric characters. Merriam-Webster suggests that the term "alphanumeric" may often additionally refer to other symbols, such as punctuation and mathematical symbols. In the POSIX/C locale, there are either 36 (A–Z and 0–9, case insensitive) or 62 (A–Z, a–z and 0–9, case-sensitive) alphanumeric characters. Subsets of alphanumeric used in human interfaces When a string of mixed alphabets and numerals is presented for human interpretation, ambiguities arise. The most obvious is the similarity of the letters I, O and Q to the numbers 1 and 0. Therefore, depending on the application, various subsets of the alphanumeric were adopted to avoid misinterpretation by humans. In passenger aircraft, aircraft seat maps and seats were designate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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