File Fixity
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File Fixity
File fixity is a digital preservation term referring to the property of a digital file being fixed, or unchanged. Fixity checking is the process of verifying that a digital object has not been altered or corrupted. During transfer, a repository may run a fixity check to ensure a transmitted file has not been altered en route. Within the repository, fixity checking is used to ensure that digital files have not been affected by data rot or other digital preservation dangers. By itself, fixity checking does not ensure the preservation of a digital file. Instead, it allows a repository to identify which corrupted files to replace with a clean copy from the producer or from a backup. In practice, a fixity check is most often accomplished by computing checksum or cryptographic hash function values for a file and comparing them to a stored value or through digital signatures. File fixity figures prominently in Preservation Metadata: Implementation Strategies (PREMIS), the Government Printi ...
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Digital Preservation
In library and archival science, digital preservation is a formal endeavor to ensure that digital information of continuing value remains accessible and usable. It involves planning, resource allocation, and application of preservation methods and technologies,Day, Michael. "The long-term preservation of Web content". Web archiving (Berlin: Springer, 2006), pp. 177-199. . and it combines policies, strategies and actions to ensure access to reformatted and "born-digital" content, regardless of the challenges of media failure and technological change. The goal of digital preservation is the accurate rendering of authenticated content over time.Evans, Mark; Carter, Laura. (December 2008). The Challenges of Digital Preservation. Presentation at the Library of Parliament, Ottawa. The Association for Library Collections and Technical Services Preservation and Reformatting Section of the American Library Association, defined digital preservation as combination of "policies, strategies and ...
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Data Rot
Bit rot may refer to: * " Bit Rot", a short story by Charles Stross * Data rot, the decay of electromagnetic charge in a computer's storage ** Disc rot Disc rot is the tendency of CD, DVD, or other optical discs to become unreadable because of physical or chemical deterioration. The causes include oxidation of the reflective layer, physical scuffing and abrasion of disc, reactions with contamina ..., the deterioration of optical media such as DVDs and CDs * Software rot, the deterioration of unmaintained software {{disambig ...
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Checksum
A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data integrity but are not relied upon to verify data authenticity. The procedure which generates this checksum is called a checksum function or checksum algorithm. Depending on its design goals, a good checksum algorithm usually outputs a significantly different value, even for small changes made to the input. This is especially true of cryptographic hash functions, which may be used to detect many data corruption errors and verify overall data integrity; if the computed checksum for the current data input matches the stored value of a previously computed checksum, there is a very high probability the data has not been accidentally altered or corrupted. Checksum functions are related to hash functions, fingerprints, randomization functi ...
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Cryptographic Hash Function
A cryptographic hash function (CHF) is a hash algorithm (a map of an arbitrary binary string to a binary string with fixed size of n bits) that has special properties desirable for cryptography: * the probability of a particular n-bit output result (hash value) for a random input string ("message") is 2^ (like for any good hash), so the hash value can be used as a representative of the message; * finding an input string that matches a given hash value (a ''pre-image'') is unfeasible, unless the value is selected from a known pre-calculated dictionary (" rainbow table"). The ''resistance'' to such search is quantified as security strength, a cryptographic hash with n bits of hash value is expected to have a ''preimage resistance'' strength of n bits. A ''second preimage'' resistance strength, with the same expectations, refers to a similar problem of finding a second message that matches the given hash value when one message is already known; * finding any pair of different messa ...
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Digital Signatures
A digital signature is a mathematical scheme for verifying the authenticity of digital messages or documents. A valid digital signature, where the prerequisites are satisfied, gives a recipient very high confidence that the message was created by a known sender ( authenticity), and that the message was not altered in transit (integrity). Digital signatures are a standard element of most cryptographic protocol suites, and are commonly used for software distribution, financial transactions, contract management software, and in other cases where it is important to detect forgery or tampering. Digital signatures are often used to implement electronic signatures, which includes any electronic data that carries the intent of a signature, but not all electronic signatures use digital signatures.

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Implementation Strategies (PREMIS)
Implementation is the realization of an application, or execution of a plan, idea, model, design, specification, standard, algorithm, or policy. Industry-specific definitions Computer science In computer science, an implementation is a realization of a technical specification or algorithm as a program, software component, or other computer system through computer programming and deployment. Many implementations may exist for a given specification or standard. For example, web browsers contain implementations of World Wide Web Consortium-recommended specifications, and software development tools contain implementations of programming languages. A special case occurs in object-oriented programming, when a concrete class implements an interface; in this case the concrete class is an ''implementation'' of the interface and it includes methods which are ''implementations'' of those methods specified by the interface. Information technology In the information technology during in ...
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United States Government Publishing Office
The United States Government Publishing Office (USGPO or GPO; formerly the United States Government Printing Office) is an agency of the legislative branch of the United States Federal government. The office produces and distributes information products and services for all three branches of the Federal Government, including U.S. passports for the Department of State as well as the official publications of the Supreme Court, the Congress, the Executive Office of the President, executive departments, and independent agencies. An act of Congress changed the office's name to its current form in 2014. History The Government Printing Office was created by congressional joint resolution () on June 23, 1860. It began operations March 4, 1861, with 350 employees and reached a peak employment of 8,500 in 1972. The agency began transformation to computer technology in the 1980s; along with the gradual replacement of paper with electronic document distribution, this has led to a st ...
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