A mid- squares hash code is produced by squaring the input and extracting an appropriate number of middle digits or bits. For example, if the input is 123,456,789 and the hash table size 10,000, squaring the key produces 1.524157875019e16, so the hash code is taken as the middle 4 digits of the 17-digit number (ignoring the high digit) 8750. The mid-squares method produces a reasonable hash code if there are not a lot of leading or trailing zeros in the key. This is a variant of multiplicative hashing, but not as good, because an arbitrary key is not a good multiplier.
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Hash functions are used in conjunction with Hash table to store and retrieve data items or data records. The hash function translates the key associated with each datum or record into a hash code which is used to index the hash table. When an item is to be added to the table, the hash code may index an empty slot (also called a bucket), in which case the item is added to the table there. If the hash code indexes a full slot, some kind of collision resolution is required: the new item may be omitted (not added to the table), or replace the old item, or it can be added to the table in some other location by a specified procedure.
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If the key is the hash code of the element, the map is essentially a set. If it's just an increasing number, it becomes a list. Maps are implemented by java.util.HashMap, java.util.
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Edge-notched card with data for a bibliographic item. Edges have not yet been notched. A superimposed code such as Zatocoding is a kind of hash code that was popular in marginal punched-card systems.
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In encryption, the confidentiality of a message is guaranteed. Hash functions can be used to verify digital signatures, so that when signing documents via the Internet, the signature is applied to one particular individual. Much like a hand-written signature, these signatures are verified by assigning their exact hash code to a person. Furthermore, hashing is applied to passwords for computer systems.
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The hash code for each file is stored in a Hash Index Table (HIT) which is the second sector of the directory. Each position in this table corresponds to a specific directory entry record. The hash table, being one sector in length, can index a maximum of 256 directory records or files. The directory itself is sized according to disk capacity by being a maximum of one cylinder (up to 34 sectors).
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Aho, Sethi, Ullman, 1986, Compilers: Principles, Techniques and Tools, pp.435. Addison-Wesley, Reading, MA. This hash function offsets the bytes 4 bits before ADDing them together. When the quantity wraps, the high 4 bits are shifted out and if non-zero, XORed back into the low byte of the cumulative quantity. The result is a word size hash code to which a modulo or other reducing operation can be applied to produce the final hash index.
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A folding hash code is produced by dividing the input into n sections of m bits, where 2^m is the table size, and using a parity- preserving bitwise operation like ADD or XOR, to combine the sections. The final operation is a mask or shift to trim off any excess bits at the high or low end. For example, for a table size of 15 bits and key value of 0x0123456789ABCDEF, there are 5 sections 0x4DEF, 0x1357, 0x159E, 0x091A and 0x8. Adding, we obtain 0x7AA4, a 15-bit value.
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Analogous to the way an ASCII or EBCDIC character string representing a decimal number is converted to a numeric quantity for computing, a variable length string can be converted as (x0ak−1+x1ak−2+...+xk−2a+xk−1). This is simply a polynomial in a non-zero "radix" a!=1 that takes the components (x0,x1,...,xk−1) as the characters of the input string of length k. It can be used directly as the hash code, or a hash function applied to it to map the potentially large value to the hash table size.
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Peers that provide a complete file are called seeders, and the peer providing the initial copy is called the initial seeder. The exact information contained in the torrent file depends on the version of the BitTorrent protocol. By convention, the name of a torrent file has the suffix `.torrent`. Torrent files have an "announce" section, which specifies the URL of the tracker, and an "info" section, containing (suggested) names for the files, their lengths, the piece length used, and a SHA-1 hash code for each piece, all of which are used by clients to verify the integrity of the data they receive.
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Modern microprocessors will allow for much faster processing, if 8-bit character strings are not hashed by processing one character at a time, but by interpreting the string as an array of 32 bit or 64 bit integers and hashing/accumulating these "wide word" integer values by means of arithmetic operations (e.g. multiplication by constant and bit-shifting). The final word, which may have unoccupied byte positions, is filled with zeros or a specified "randomizing" value before being folded into the hash. The accumulated hash code is reduced by a final modulo or other operation to yield an index into the table.
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One of the main differences between a digital signature and a written signature is that the user does not "see" what he signs. The user application presents a hash code to be signed by the digital signing algorithm using the private key. An attacker who gains control of the user's PC can possibly replace the user application with a foreign substitute, in effect replacing the user's own communications with those of the attacker. This could allow a malicious application to trick a user into signing any document by displaying the user's original on-screen, but presenting the attacker's own documents to the signing application.
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In 2009 ElcomSoft released a tool that takes WPA/WPA2 Hash Codes and uses brute-force methods to guess the password associated with a wireless network. The brute force attack is carried out by testing passwords with a known SSID of a network of which the WPA/WPA2 Hash Code has been captured. The passwords that are tested are generated from a dictionary using various mutation (genetic algorithm) methods, including case mutation (password, PASSWORD, PassWOrD, etc.), year mutation (password, password1992, password67, etc.), and many other mutations to try to guess the correct password. The advantages of using such methods over the traditional ones, such as rainbow tables, are numerous.
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The hash join is an example of a join algorithm and is used in the implementation of a relational database management system. All variants of hash join algorithms involve building hash tables from the tuples of one or both of the joined relations, and subsequently probing those tables so that only tuples with the same hash code need to be compared for equality in equijoins. Hash joins are typically more efficient than nested loops joins, except when the probe side of the join is very small. They require an equijoin predicate (a predicate comparing records from one table with those from the other table using a conjunction of equality operators '=' on one or more columns).
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If the data to be hashed is small enough, one can use the data itself (reinterpreted as an integer) as the hashed value. The cost of computing this identity hash function is effectively zero. This hash function is perfect, as it maps each input to a distinct hash value. The meaning of "small enough" depends on the size of the type that is used as the hashed value. For example, in Java, the hash code is a 32-bit integer. Thus the 32-bit integer `Integer` and 32-bit floating-point `Float` objects can simply use the value directly; whereas the 64-bit integer `Long` and 64-bit floating-point `Double` cannot use this method.
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While all methods require physical security on the paper ballots, method 1 also requires enough security on the cast vote records so no one can change them. This can be accomplished by computer-calculating, storing and comparing a hash code for each file of cast vote records: (a) right after the election, (b) when independent tabulation is done, and (c) when ballot comparison is done. Colorado says it has a system to do the independent count of cast vote records, but it is not yet publicly documented, so the chance of bugs or hacks affecting this independent computer at the Secretary of State's office along with one or more of the election machines is unknown. California's process for risk-limiting audits omits the step of independent totals.
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A small phone book as a hash table In computing, a hash table (hash map) is a data structure that implements an associative array abstract data type, a structure that can map keys to values. A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired value can be found. During lookup, the key is hashed and the resulting hash indicates where the corresponding value is stored. Ideally, the hash function will assign each key to a unique bucket, but most hash table designs employ an imperfect hash function, which might cause hash collisions where the hash function generates the same index for more than one key.
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Rainbow tables, being very large in size because of the amount of SSID/Password combinations saved, take a long time to traverse, cannot have large numbers of passwords per SSID, and are reliant on the SSID being a common one which the rainbow table has already listed hash codes for (Common ones include linksys, belkin54g, etc.). EWSA, however, uses a relatively small dictionary file (a few megabytes versus dozens of gigabytes for common rainbow tables) and creates the passwords on the fly as needed. Rainbow tables are tested against a captured WPA/WPA2 Hash Code via a computer's processor with relatively low numbers of simultaneous processes possible. EWSA, however, can use a computer's processor(s), with up to 32 logical cores, up to 8 GPUs, all with many CUDA cores (NVIDIA) or Stream Processors (ATI).
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During the SBS interview, the integrity of the chatroom file was discussed and said to have a tamper-proof device, technically a hash-code verification, showing that the file had not been manipulated; and could stand as circumstantial evidence to seek more evidence. Bang, an economics graduate of Seoul National University said of the chats, "Their conversations showed that there were not only sex crimes by celebrities, but also a cozy relationship between them and top police officers," and, "It is someone higher up than [the Gangnam Police Precinct chief]." The phone belonged to Jung, who was in Los Angeles filming for another television show when the chatroom leaks reached him. He hurriedly returned to Seoul on March 12, where he was booked as a suspect on charges of illegal hidden camera filming and sharing and accused of taping ten or more women.
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During the SBS interview, the integrity of the chat room file was discussed, and was said to have a tamper-proof device, technically a hash-code verification, showing that the file had not been manipulated; and could stand as circumstantial evidence to seek more evidence. Bang, an economics graduate of Seoul National University, and a practicing lawyer, said of the chats, "Their conversations showed that there were not only sex crimes by celebrities, but also a cozy relationship between them and top police officers," and "It is someone higher up than [the Gangnam Police Precinct chief]." Traffic on Bongeunsa-ro, Yeoksam-dong, Gangnam. Le Meridien Hotel, location of Club Burning Sun on left. Also, on Monday, March 11, due to possible police involvement, the Commission, a watchdog agency, turned the records over to the Supreme Prosecutors' Office of the Republic of Korea, asking them to investigate the scandal instead of the police. Within a week, the case was transferred to the Seoul Central District Prosecutors’ Office who said they would assign a team to direct the SMPA's investigation.
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