What Is the MD5 Hashing Algorithm and How Does It Work? (2024)

What is MD5?

MD5 (message-digest algorithm) is a cryptographic protocol used for authenticating messages as well as content verification and digital signatures. MD5 is based on a hash function that verifies that a file you sent matches the file received by the person you sent it to. Previously, MD5 was used for data encryption, but now it’s used primarily for authentication.

How does MD5 work?

MD5 runs entire files through a mathematical hashing algorithm to generate a signature that can be matched with an original file. That way, a received file can be authenticated as matching the original file that was sent, ensuring that the right files get where they need to go.

The MD5 hashing algorithm converts data into a string of 32 characters. For example, the word “frog” always generates this hash: 938c2cc0dcc05f2b68c4287040cfcf71. Similarly, a file of 1.2 GB also generates a hash with the same number of characters. When you send that file to someone, their computer authenticates its hash to ensure it matches the one you sent.

If you change just one bit in a file, no matter how large the file is, the hash output will be completely and irreversibly changed. Nothing less than an exact copy will pass the MD5 test.

What is MD5 used for?

MD5 is primarily used to authenticate files. It’s much easier to use the MD5 hash to check a copy of a file against an original than to check bit by bit to see if the two copies match.

MD5 was once used for data security and encryption, but these days its primary use is authentication. Because a hacker can create a file that has the exact same hash as an entirely different file, MD5 is not secure in the event that someone tampers with a file. But if you’re simply copying a file from one place to another, MD5 will do the job.

Since MD5 is no longer used for encryption purposes, if you need to secure your files, you should consider getting the best encryption software you can find or learning how to turn on WiFi encryption in your router settings.

And if you want to encrypt your entire internet connection, try Avast SecureLine VPN. Unlike MD5, a VPN encrypts all the data moving in and out of your computer, making it completely invisible to hackers, ISPs, governments, or anyone else. And with Avast, you’ll enjoy lightning-fast connection speeds.

How is an MD5 hash calculated?

The MD5 hashing algorithm uses a complex mathematical formula to create a hash. It converts data into blocks of specific sizes and manipulates that data a number of times. While this is happening, the algorithm adds a unique value into the calculation and converts the result into a small signature or hash.

MD5 algorithm steps are incredibly complex for a reason — you cannot reverse this process and generate the original file from the hash. But the same input will always produce the same output, also known as the MD5 sum, hash, or the checksum. That’s what makes them so useful for data validation.

An MD5 hash example looks like this: 0cc175b9c0f1b6a831c399e269772661. That’s the hash for the letter “a.”

But a hacker with a very powerful computer can make a malicious file generate the same hash as a harmless one. So, when you think you’re receiving a normal file, you might be getting something nasty like ransomware instead — or a different kind of malware.

When this happens, and two distinct files share the same hash, it’s called MD5 collision, which can happen accidentally or on purpose.

An MD5 collision attack occurs when a hacker intentionally sends a malicious file with the same hash as a clean file.

If you’ve gotten ransomware this way — or any other way — check out our guide to removing ransomware from your PC immediately. One of the most dangerous types of ransomware in recent years is a strain called CryptoLocker ransomware, which wreaked havoc even after removal.

How many bytes long is an MD5 hash?

An MD5 hash is 16 bytes. Each MD5 hash looks like 32 numbers and letters, but each digit is in hexadecimal and represents four bits. Since a single character represents eight bits (to form a byte), the total bit count of an MD5 hash is 128 bits. Two hexadecimal characters form a byte, so 32 hexadecimal characters equal 16 bytes.

The MD5 length will always be the same: a 128-bit hash.

The process where a single letter gets converted to a 32-character output is called padding, which forms a part of the hash calculation. If a bunch of data doesn’t match the length needed to proceed with MD5 calculation, bits are added to reach some multiple of 512 bits.

MD4 vs MD5: what's the difference?

MD4 was considered not secure because its hash calculation wasn’t sufficiently complex. While MD4 hashes resemble MD5 hashes, there’s a lot more going on behind the scenes with MD5 — many more steps were added to the calculation to increase complexity.

MD5 was secure enough for many years, but these days it’s no longer complex enough for cryptographic purposes and data encryption. Computers have become powerful enough to crack MD5 hashes easily, and a new standard is needed.

Which is better, MD5 or SHA?

A hashing algorithm needs to occupy the “sweet spot” of complexity — not so complex that it becomes cumbersome to use, but not so simple that it can be easily broken. Now, MD5 collisions are simply too easy to attain with current processing power.

SHA (Secure Hash Algorithm) addresses MD5’s vulnerabilities, giving new life to the security applications of hash algorithms. SHA outputs a longer string of hexadecimal characters, so you can easily tell the difference between the two types. This is a big reason why SHA is more secure, because a greater number of bits increases complexity exponentially.

When security isn’t a concern, MD5 is sufficient, and it’s still a great option for data verification.

What is the best hashing algorithm?

While there’s no “best” hashing algorithm, there are hashing algorithms that are better depending on the use and application.

MD5 might not have the best security, but you can trust an MD5 hash from a known, secure website. MD5 calculates faster than SHA, making it a convenient solution for software vendors like OpenOffice. You can ensure the installation file matches the file on the website with the MD5 hash.

SHA-256 is widely used for website authentication and data encryption. Secure websites usually have an SSL certificate. SSL (Secure Socket Layer) encrypts data moving between you and the website you’re using, and it does so with SHA-256. If you want even greater security and data encryption, use a VPN.

Why all this talk about encryption? Imagine if someone could read the entire thread between you and a friend on WhatsApp. The reason they can’t is because of end-to-end encryption.

Keep your data secure with Avast SecureLine VPN

While true data privacy is at a premium these days; it should be a given. Thankfully, Avast SecureLine VPN offers airtight security for your data and your entire internet connection. No one will see what you’re doing — not snoops or government agencies — and personal information like your credit card details will stay hidden. While MD5 no longer offers sufficient encryption protection, Avast SecureLine VPN certainly does.