What Is MD5? | Message-Digest Algorithm & MD5 Hashing
Secure communications are more important than ever - and also more accessible, thanks to cryptography and hashing functions like SHA-1 and bcrypt. MD5 (Message-Digest Algorithm 5) is one example of a cryptographic hashing algorithm used today to verify that the receiver of information gets the exact same message that was sent. In this article, learn what MD5 is, how it works, and how we use it.
What is MD5?
MD5, or Message-Digest Algorithm 5, is a cryptographic hash function designed to produce a unique, fixed-size 128-bit hash value from input data of any size. This hash value is what we call a message digest.
We normally use message digest to authenticate files. MD5 verifies data against corruption, ensuring a file was not altered during transmission or storage.
MD5 generates a unique hash value for each unique input. If even a single bit of the original data changes, the resulting hash will vastly differ. This key property makes the algorithm useful for tasks like checking the authenticity of digital signatures.
Cryptographic hash algorithms, including Message-Digest Algorithm 5, are one-way functions. This means they transform data into unique hashes that can’t be reversed to recover the original data.
When data is hashed, MD5 generates a hash value that uniquely represents the original data. If the hash value of the received data matches the original hash, it confirms that the data is identical to the original and hasn't been tampered with.
MD5's popularity is due to its simplicity and speed. Although MD5 is still recognized today, it is no longer powerful for many modern applications and has been considered less secure since 2005.
Cryptographic researchers have discovered that MD5 is susceptible to collision attacks, in which two inputs produce the same hash value. These vulnerabilities undermine MD5's reliability for cryptographic security purposes because attackers can exploit these weaknesses to forge data and bypass security measures.
In light of these vulnerabilities, more secure hash functions, like SHA-256 and SHA-3, superseded MD5.
History of Message-Digest Algorithm 5
Message Digest Algorithm 5 has a significant history in cryptography. It was designed by Ronald Rivest of RSA Data Security in 1991 as an improvement for MD4 and specified in RFC 1321 in 1992.
The increasing need for data security further propelled the adoption of MD5. MD5 is commonly used as a checksum to ensure data integrity. Despite its historical use as a cryptographic hash algorithm, MD5 has been found to have several significant vulnerabilities over time.
However, it remains useful for various non-cryptographic tasks, such as determining the partition for a particular key in a partitioned database. This is largely due to its lower CPU usage when compared to more modern hash functions.
In 1993, researchers Den Boer and Bosselaers made an early but limited breakthrough by discovering a "pseudo-collision" in the MD5 compression function. In this, two different initialization vectors produce the same digest.
By 1996, Hans Dobbertin identified actual collisions within the MD5 compression function. Although this attack didn't compromise the entire MD5 hash algorithm, it was sufficient to raise alarms within the cryptographic community.
This led to recommendations to transition to alternative algorithms like SHA-1. One major weakness of MD5 is its relatively short hash value of 128 bits, making it susceptible to brute force collision attacks.
A practical demonstration of MD5's vulnerability was undertaken by the MD5CRK project, launched in March 2004. The project aimed to find a collision using a birthday attack, which is a type of brute force collision attack, to highlight the practical risks associated with MD5.
In subsequent years, further advancements in computing power made MD5 even more vulnerable. Major organizations, including NIST (National Institute of Standards and Technology), deprecated using MD5 for digital signatures.
MD5 is still used today to file integrity checks, though alternatives now exist.
How does MD5 work?
A hash function is a mathematical algorithm that transforms input data into a fixed-size string of characters, which appears random.
For Message-Digest Algorithm 5, this fixed-size output is a 128-bit hash value. The goal of a hash function is to ensure that even a small change in the input data results in a significantly different hash value. There are a few steps to the algorithm: input padding, initializing the buffers, processing the message, adding the results, and outputting the final hash.
Step one: Input padding
The input message is first padded so that its length is a multiple of 512 bits. Padding involves:
- Appending a single '1' bit to the message.
- Adding '0' bits until the length of the message is congruent to 448 modulo 512.
- Appending the length of the original message (before padding) as a 64-bit integer. This ensures that the total length of the padded message is a multiple of 512 bits.
Step two: Initializing the MD buffers
Message-Digest Algorithm 5 uses four 32-bit variables (A, B, C, D) initialized to specific constants. These variables will hold the intermediate and final hash values.
- A = 0x67452301
- B = 0xEFCDAB89
- C = 0x98BADCFE
- D = 0x10325476
Step three: Processing the message in 512-bit blocks
The padded message is divided into 512-bit blocks. Each block is processed in 64 steps, divided into four rounds of 16 operations. Each step involves a non-linear function, modular addition, and bitwise operations (left rotations). The main functions used in these steps are:
- F (B, C, D) = (B AND C) OR ((NOT B) AND D)
- G (B, C, D) = (B AND D) OR (C AND (NOT D))
- H (B, C, D) = B XOR C XOR D
- I (B, C, D) = C XOR (B OR (NOT D))
Each round uses one of these functions combined with a 32-bit constant and a specific part of the current 512-bit block.
Step four: Adding the result to the current hash value
After processing each 512-bit block, the results are added to the current values of the buffers (A, B, C, D). This is done using modular addition (addition modulo 2^32).
Step five: Outputting the final hash value
After all the 512-bit blocks process, the buffers A, B, C, and D are concatenated to form the final 128-bit hash value. You see this value typically represented as a 32-character hexadecimal number.
Uses of MD5 algorithm
Though the MD5 algorithm isn't the most commonly-used algorithm in our present day, it still has many uses.
- Data integrity and encryption. Message-Digest Algorithm 5 verifies the integrity of data. It generates an MD5 hash of a file before and after transmission. If the hash values match, the data is intact, and the file is secured from eavesdropping.
- Create digital signatures. To authenticate the origin of a message or document, MD5 hashes the message and encrypts the hash with a private key to generate a digital signature. The recipient can then decrypt the signature with the sender's public key and compare the hash to verify authenticity.
- Password storage and authentication. In some systems, Message-Digest Algorithm 5 hashes passwords before storing them in databases. This practice scrambles the actual password even in the case of a database compromise. However, due to MD5's vulnerabilities, experts recommend other hash functions for secure password storage.
- File verification and duplicate detection. The algorithm identifies identical files. If two files have the same MD5 hash, they are identical. Message-Digest Algorithm 5 also detects modified files in cloud storage systems.
When a file is modified, its MD5 hash changes.
Advantages and disadvantages of MD5
Like all algorithms and protocols, MD5 has both advantages and disadvantages. The key advantages of the MD5 algorithm are:
- Fast computation. Many know MD5 for its fast computation and straightforward implementation.
- 128-bit hash values. It generates a 128-bit (16-byte) hash value to create compact representations of data.
- Requires low memory. Integrating MD5 requires relatively low memory. This is beneficial for systems with limited resources.
- Simple process. Generating an MD5 hash (digest) from an original message is simple and quick.
- Easy to compare files. It’s pretty easy to compare hashes between files.
On the other hand, however, hash collisions and preimage attacks defeat the purpose of the MD5 authentication tool. Furthermore, MD5 is not as robust as it once was. Other algorithms, like SHA-256, produce 256-bit hashes rather than the 128-bit hashes produced by MD5.
MD5 vs. other hashing algorithms
There are a set of modern hashing algorithms that address the shortcomings of MD5. They create more complex hashes to tighten the security of digital data.
Here is an overview of some alternatives to MD5.
- Secure Hash Algorithm 1 (SHA-1): While it produces a longer 160-bit hash, SHA-1 is vulnerable to collision attacks. It's generally not recommended for new applications.
- Secure Hash Algorithm 2 (SHA-2): This family includes SHA-224, SHA-256, SHA-384, and SHA-512, offering varying levels of security and hash lengths. SHA-256 and SHA-512 are particularly popular for their strong security properties and are widely used in applications like blockchain.
- Secure Hash Algorithm 3 (SHA-3): SHA-3 is the latest in the SHA family. It uses a different construction (Keccak) and can produce hash values of variable lengths. The hash function offers robust security but organizations implement it less commonly due to its complexity and the need for system updates.
- Cyclic redundancy check (CRC) codes: While not true hash functions, CRC codes are used for error-checking in data transmission. They are faster but less secure compared to cryptographic hash functions like SHA.
Frequently asked questions
Is MD5 secure?
The IETF considers Message-Digest Algorithm 5 “broken.” In the past years, there have been a large number of attacks against MD5 hashes; hence, it is not a secure method for cryptographic authentication.
What are hash collisions?
Hash collisions happen when different inputs result in the same hash. MD5 is vulnerable to them.
Can you decrypt MD5?
No. Message-Digest Algorithm 5 is a hash function, not encryption, so it's one-way and can't be reversed to reveal the original data.
