File verification is the process of using an algorithm for verifying the integrity or authenticity of a computer file. In Mathematics, Computing, Linguistics and related subjects an algorithm is a sequence of finite instructions often used for Calculation Authentication (from Greek αυθεντικός real or genuine from authentes author is the act of establishing or confirming something (or someone as A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually This can be done by comparing two files bit-by-bit, but requires two copies of the same file, and may miss systematic corruptions which might occur to both files. A more popular approach is to also store checksums (hashes) of files for later comparison. A checksum is a form of Redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space ( Telecommunications
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Integrity verification
File integrity can be compromised, usually referred to as the file becoming corrupted. Data corruption refers to errors in Computer Data that occur during transmission or retrieval introducing unintended changes to the original data A file can become corrupted by a variety of ways: faulty storage media, errors in transmission, write errors during copying or moving, software bugs, and so on. A data storage device is a device for recording (storing information (data A software bug (or just “bug” is an error flaw mistake Failure, fault or “undocumented feature” in a Computer program that prevents it
Hash-based verification ensures that a file has not been corrupted by comparing the file's hash value to a previously calculated value. A hash function is any well-defined procedure or mathematical function for turning some kind of Data into a relatively small integer, that may If these values match, the file is presumed to be unmodified. Due to the nature of hash functions, hash collisions may result in false positives, but the likelihood of collisions is often negligible with random corruption. In Computer science, a hash collision or hash clash is a situation that occurs when two distinct inputs into a Hash function produce identical outputs In Statistics, the terms Type I error (also α error, or false positive) and type II error ( β error, or a false negative
Authenticity verification
It is often desirable to verify that a file hasn't been modified in transmission or storage by untrusted parties, for example, to include malicious code such as viruses or backdoors. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable A backdoor in a Computer system (or Cryptosystem or Algorithm) is a method of bypassing normal Authentication, securing remote access to a computer To verify the authenticity, a classical hash function is not enough since they are not designed to be collision resistant; it is computationally trivial for an attacker to cause deliberate hash collisions, meaning that a malicious change in the file is not detected with by a hash comparison. Collision resistance is a property of Cryptographic hash functions: a hash function is collision resistant if it is hard to find two inputs that hash to the same output (that In cryptography, this attack is called the collision attack. A birthday attack is a type of cryptographic attack so named because it exploits the Mathematics behind the Birthday problem in Probability theory
For this purpose, cryptographic hash functions are employed often. A cryptographic Hash function is a transformation that takes an input (or 'message' and returns a fixed-size string which is called the hash value (sometimes As long as the hash sums cannot be tampered with — for example, if they are communicated over a secure channel — the files can be presumed to be intact. Alternatively, digital signatures can be employed to assure tamper-resistance. A digital signature or digital signature scheme is a type of asymmetric cryptography used to simulate the security properties of a handwritten Signature
File formats
See also
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