A hashed password typically appears as a long, seemingly random string of alphanumeric characters, often presented in hexadecimal format. It's the fixed-length output of a cryptographic hash function, designed to be irreversible.
The Appearance of a Hashed Password
A hashed password doesn't resemble the original password in any way. Instead, it looks like a jumble of characters and numbers. For instance, a hash produced by a secure algorithm might look like 5d41402abc4b2a76b9719d911017c592. This output is specifically designed so that you cannot derive the original password from it.
Key Characteristics of a Hashed Password
- Fixed Length: Regardless of how long or short the original password is, the generated hash will always have a specific, fixed length determined by the hashing algorithm used.
- Hexadecimal Format: Most hash outputs are represented using hexadecimal characters (0-9 and a-f), which is a common way to display binary data compactly.
- Appears Random: The characters in a hash appear entirely random, with no obvious patterns or sequences that relate back to the original password. Even a minor change in the input password will result in a drastically different hash (the "avalanche effect").
- One-Way Function: Hashing is a one-way process. While you can easily generate a hash from a password, it's computationally infeasible to reverse the hash to get the original password.
The Role of Salting in Hashed Passwords
Modern password hashing doesn't just hash the password directly. A crucial security measure called salting is involved, which makes hashed passwords even more robust against common attacks.
Before a password is hashed, a unique, random string called a salt is generated and combined with the user's password. This combined string (password + salt) is then hashed using a secure algorithm. Both this salt and the resulting hash are stored in the database.
During login, when a user enters their password, the system retrieves the stored salt associated with that user. It then combines the entered password with this stored salt and hashes this new combined string. The newly generated hash is then compared to the previously stored hash to verify the user's identity. This process ensures that identical passwords used by different users will produce different hashes because they will be combined with different salts.
Common Hashing Algorithms and Their Outputs
Different hashing algorithms produce hashes of varying lengths and appearances. While some older algorithms like MD5 are no longer considered secure for password hashing due to vulnerabilities, newer, more robust algorithms are widely used.
Here are examples of what hashed passwords (or general hash outputs) might look like from different algorithms:
| Algorithm Type | Typical Length (Characters) | Example Output | Notes |
|---|---|---|---|
| MD5 | 32 | d1702f30453c072b2230ef1d234a4087 |
Not Recommended for passwords; vulnerable. |
| SHA-1 | 40 | 69d95d86211833116541f4a9b581e012e86b0388 |
Not Recommended for passwords; theoretically broken. |
| SHA-256 | 64 | 5f77833072a31969a5a3a2a613247063d8916d559828e82ef4c665e7ce0c7c8a |
Widely used, but often combined with salting and iteration. |
| Bcrypt | Typically 60 (variable) | $2a$10$QWzK9Gq.r3Z2oY0J8VzM5.uz.dC4x7jV6tP5M7E8S9F0G1H2I3J4 |
Includes algorithm version, cost factor, salt, and hash within the string. Recommended. |
| Scrypt | Variable (often longer) | $s0$e0801$1f9d6c... (complex structure) |
Similar to bcrypt, designed to be memory-hard. Recommended. |
Note: The example for Bcrypt includes metadata like the algorithm version, cost factor (iteration count), and the salt itself, followed by the actual hash, all combined into one string for storage.
Why Hashed Passwords Look This Way
The design of hashed passwords as complex, fixed-length strings is rooted in fundamental security principles:
- Data Security: If a database storing user information is compromised, attackers will only get these seemingly random hashes, not the actual plaintext passwords. This prevents them from easily logging into other services where users might reuse passwords.
- Integrity Verification: Hashes are also used to verify data integrity. If even one character of the stored hash is altered, it will no longer match the hash generated during login, indicating tampering or an incorrect password.
- Preventing Brute-Force and Dictionary Attacks: While an attacker can't reverse a hash, they could try to guess passwords, hash them, and compare them to the stored hashes. Strong, slow hashing algorithms (like Bcrypt or Scrypt) combined with salting significantly slow down this process, making such attacks impractical.
By transforming passwords into these unique, irreversible strings and storing them with their respective salts, systems significantly enhance the security of user accounts.
