What is Hashing?
Hashing is the process of taking input data of any length and transforming it into a fixed-length string (a hash value) that appears random.
The most critical characteristic of hashing is that it is “one-way” or irreversible—you cannot reconstruct the original data from its hash.
Primary Goals of Hashing
- Password Storage: By storing hash values instead of plain-text passwords, you minimize the damage if your database is ever compromised.
- Data Integrity: Comparing hash values allows you to verify that a file or message hasn’t been altered during transmission.
Ensuring Secure Hashing
In modern systems, simply hashing a value is not enough.
- SHA-256 / SHA-512: These are the currently recommended secure algorithms. Avoid using MD5 or SHA-1 for security purposes, as they have known vulnerabilities.
- Salting: This involves appending a unique “random string” (the salt) to a password before hashing it. This prevents rainbow table attacks (using pre-calculated lists of hash values).
HMAC (Keyed-Hash Message Authentication Code)
HMAC is a mechanism for authenticating a message by combining a hash function with a “secret key.”
- The sender calculates an HMAC value using the “data” and a “secret key” and sends both the data and the HMAC.
- The receiver calculates the HMAC using the same “data” and “secret key” and checks if it matches the received HMAC.
This verifies both Integrity (the data hasn’t been changed) and Authenticity (the message came from the correct sender). It’s widely used in Web API authentication and Webhook verification.
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⚠️ Note: While different data can theoretically produce the same hash (a collision), it is computationally infeasible to intentionally cause a collision with modern algorithms.