Question 1

Step 2: Apply the polynomial expansion.

Accepted Answer

We multiply each character's value by our prime number $31$ raised to a decreasing power.

Question 2

Step 3: Sum the terms.

Accepted Answer

$Total = 65,348 + 2,449 + 71 = 67,868$

Question 3

Step 4: Apply the Modulo.

Accepted Answer

We take the total and find the remainder when divided by our maximum size $M$ (100,000).
$H("DOG") = 67,868 \pmod{100,000} = 67868$.
The final hash digest for "DOG" is 67868.

Question 4

Hashing vs. Encryption (e.g., SHA-256 vs. AES-256):

Accepted Answer

Encryption is a bidirectional process designed to protect data in transit or at rest. If you encrypt a 10-page document using the Advanced Encryption Standard (AES-256) and a secret key, the output will be roughly the size of a 10-page document. You can then transmit this scrambled data to a colleague, who uses the same secret key to reverse the process and read the document. Hashing is a unidirectional process designed for verification. If you hash the same 10-page document, the output is exactly 64 characters long. You cannot send the hash to a colleague and expect them to read the document. You use encryption when the data needs to be hidden but recovered later; you use hashing when you only need to prove that the data hasn't been altered.

Question 5

Hashing vs. Encoding (e.g., SHA-256 vs. Base64):

Accepted Answer

Encoding is merely a translation of data into a different format for compatibility purposes; it offers zero cryptographic security. Base64 encoding takes binary data (like an image) and translates it into standard ASCII text characters so it can be safely transmitted via text-based protocols like email. Anyone who possesses a Base64 string can instantly decode it back into the original image without needing a key or password. Hashing, conversely, destroys the original data format entirely to create a secure, irreversible fingerprint. A developer who attempts to "secure" a password by Base64 encoding it is essentially just translating the password into a different language, leaving it completely exposed to any attacker who knows how to translate it back.

Question 6

Hashing vs. Obfuscation:

Accepted Answer

Obfuscation is the practice of deliberately making code or data difficult for humans to read, usually to protect intellectual property or hide malicious payloads. An obfuscated JavaScript file might have all its variables renamed to single letters and its logic scrambled, but the computer can still execute the code perfectly. Obfuscation is a superficial disguise. Hashing is a mathematical destruction. You cannot execute a hashed program, nor can you read a hashed text. Where obfuscation relies on confusion, hashing relies on rigorous, mathematically proven one-way functions.

Question 7

What happens if I hash a file, change one letter, and hash it again?

Accepted Answer

Due to the cryptographic property known as the avalanche effect, changing even a single bit of data in the input file will cause a catastrophic cascade of mathematical changes throughout the algorithm. The resulting hash digest will be completely unrecognizable compared to the original hash. Approximately 50% of the characters in the new hash will change, ensuring that even microscopic tampering is immediately evident to anyone comparing the checksums.

Question 8

Can two different files produce the exact same hash?

Accepted Answer

Yes, mathematically this is called a collision, and it is an absolute certainty because there are infinite possible files but a finite number of hash outputs. However, for a modern algorithm like SHA-256, the total number of possible outputs ($2^{256}$) is so incomprehensibly large that the probability of finding a collision by chance is effectively zero. No human or supercomputer has ever found a collision in SHA-256, and it is widely believed that the energy required to compute one would exceed the energy output of the sun.

Question 9

Why do websites use salts when hashing passwords?

Accepted Answer

A salt is a random string of characters added to a user's password before it is hashed. Without a salt, every user who chooses the password "password123" will have the exact same hash in the database. Hackers exploit this by pre-computing the hashes of millions of common passwords in massive databases called "Rainbow Tables." By adding a unique, random salt to every password, the resulting hashes are completely unique, rendering Rainbow Tables useless and forcing the hacker to attack each account individually.

Question 10

Is MD5 safe to use anymore?

Accepted Answer

For cryptographic security, MD5 is completely broken and must never be used. Modern computers can mathematically engineer two different files that produce the exact same MD5 hash in a matter of seconds, allowing attackers to forge digital signatures and bypass security protocols. However, MD5 is still acceptable for non-security purposes, such as quickly checking if a file was accidentally corrupted during a network download, because it is computationally very fast.

Question 11

How do quantum computers threaten hash generators?

Accepted Answer

Quantum computers utilize qubits and quantum superposition to perform specific mathematical calculations exponentially faster than classical computers. Using Grover's Algorithm, a sufficiently powerful quantum computer could theoretically brute-force a hash function in the square root of the time it takes a normal computer. This means a 256-bit hash like SHA-256 would only offer 128 bits of security against a quantum attack. While 128 bits is still secure today, the industry is preparing to migrate to 512-bit hashes to maintain a comfortable security margin for the future.

Question 12

What is the difference between SHA-2 and SHA-3?

Accepted Answer

SHA-2 (which includes SHA-256 and SHA-512) is the current global standard, built on an older mathematical structure called the Merkle-Damgård construction. SHA-3 is the newest standard, finalized in 2015, which uses a completely different underlying mathematics called a "sponge function" (specifically the Keccak algorithm). SHA-3 was not created because SHA-2 was broken, but rather as an insurance policy. If a fatal flaw is ever discovered in the Merkle-Damgård structure, the world can instantly switch to SHA-3 without losing security.

Question 13

How long does it take to crack a SHA-256 hash?

Accepted Answer

You cannot "crack" or decrypt a hash because the process is one-way; you can only guess the original input. If you are trying to guess a 12-character random password hashed with SHA-256, a cluster of top-tier graphics cards could guess hundreds of billions of combinations per second. However, if you are trying to guess a 256-bit cryptographic key, even if you harnessed the computing power of every computer on Earth and ran them for the entire 13.8 billion-year lifespan of the universe, your chances of guessing the correct input would still be practically zero.

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