A hash value, also known as a hash code, hash sum, or simply a hash, is the output produced by a hash function. A hash function is a mathematical algorithm that takes an input (or "message") of any size and converts it into a fixed-length string of characters, which typically appears random. This fixed-length output is the hash value.
Key Characteristics of Hash Values
Fixed Length: Regardless of the size of the input, the hash value is always of a fixed length. For example, the SHA-256 hash function always produces a 256-bit hash value[2][3][17].
Deterministic: The same input will always produce the same hash value. This property ensures consistency and reliability in applications like data retrieval and integrity checks[17][18].
One-Way Function: It is computationally infeasible to reverse-engineer the original input from its hash value. This property is crucial for security applications, such as password storage and digital signatures[3][13][17].
Collision Resistance: A good hash function minimizes the probability of two different inputs producing the same hash value. This property is essential to avoid conflicts in data storage and ensure data integrity[3][13][17].
Avalanche Effect: A small change in the input should produce a significantly different hash value. This property ensures that even minor alterations in the input are detectable[17][18].
Applications of Hash Values
Data Integrity: Hash values are used to verify that data has not been altered. By comparing the hash value of the original data with the hash value of the received data, one can ensure data integrity[11][17].
Password Storage: Hash values are used to securely store passwords. Instead of storing the actual password, systems store the hash value of the password. When a user logs in, the system hashes the entered password and compares it to the stored hash value[3][9][17].
Digital Signatures: Hash values are used in digital signatures to ensure the authenticity and integrity of a message or document. The hash value of the message is encrypted with the sender's private key to create the digital signature[3][11][17].
Data Retrieval: Hash values are used in hash tables to quickly locate a data record given its search key. The hash function computes an index into an array of buckets or slots, from which the desired valu...
