Hashing in cryptography is a one-way mathematical process that takes an input (or "message") and produces a fixed-size string of characters, which is typically a hexadecimal value. The output, known as the hash value or digest, is unique to the input data, meaning that even a small change in the input will result in a completely different hash.
The main characteristics of cryptographic hash functions are:
Hash functions are widely used in various cryptographic applications, including password storage, data integrity verification, digital signatures, and blockchain technology.
In the context of password storage, hashing is used to convert user passwords into irreversible hash values. When a user creates an account or sets a password, the system takes the password, applies the hash function, and stores the resulting hash in the database. When the user attempts to log in, the entered password is hashed again, and the system compares the hash with the stored value. If they match, the password is considered correct, and the user is granted access.
Hashing is used to verify the integrity of data. Before transmitting or storing data, the system computes the hash of the data and sends or stores both the data and the hash value. When the data is later retrieved or received, the system recalculates the hash and compares it with the original hash. If they match, the data has not been tampered with.
Digital signatures involve hashing a message and then encrypting the hash value with the sender's private key. The encrypted hash, along with the original message, forms the digital signature. The recipient can verify the authenticity of the message by decrypting the signature with the sender's public key and comparing the decrypted hash with a freshly computed hash of the received message.