A hash is a fixed-length string (digest) generated from input data of any size using a hash function. The process is one-way—you cannot decrypt or reverse a hash to get the original data. That’s why "hash encryption" is a misnomer; hashing is not encryption.
Popular hash algorithms include:
MD5 (obsolete for security use)
SHA-1 (deprecated)
SHA-256, SHA-512 (part of SHA-2 family)
SHA-3
bcrypt, scrypt, Argon2 (for secure password hashing)
Hashing serves several purposes in cybersecurity and data integrity. Key reasons to use hashing include:
Data Integrity: Ensures data hasn’t been altered (e.g., file checksums).
Password Storage: Securely stores passwords by comparing hashes instead of storing actual passwords.
Digital Signatures: Hashes are signed rather than large documents.
Efficiency: Small, fixed-size hash values are faster to compare than large blocks of data.
Because hashes are deterministic and fast, they are ideal for verification tasks.
Using a hash function involves:
Inputting data (e.g., a file, string, or password).
Processing the data with a hashing algorithm.
Obtaining a digest, which is a fixed-size string that uniquely represents the input.
For password protection:
Combine the password with a salt (random data).
Apply a secure hash function (e.g., bcrypt or Argon2).
Store the resulting hash and salt securely.
Since hashes can’t be reversed, you verify input (like a password) by hashing it again and comparing the new hash to the stored one.
Hashing should be used when:
Data integrity needs to be verified (e.g., checking for corruption or tampering).
Passwords need to be securely stored (not encrypted or plain-text).
Digital signatures and certificates are involved (hashing ensures document authenticity).
Fast data comparison is necessary (e.g., in hash tables or caches).
Hashing is not suitable when you need to recover original data later—that’s what encryption is for.