What is MD5?
MD5 (Message-Digest Algorithm 5) is a widely used cryptographic hash function that produces a 128-bit (16-byte) hash value, typically expressed as a 32-character hexadecimal number. It was designed to be used as a checksum to verify data integrity.
Quick Facts
| Full Name | Message-Digest Algorithm 5 |
|---|---|
| Created | 1991 by Ronald Rivest |
| Specification | Official Specification |
How It Works
⚠️ SECURITY WARNING: MD5 is cryptographically broken and should NOT be used for security purposes. Collision attacks can be performed in seconds on modern hardware. Use SHA-256 or SHA-3 for cryptographic applications, and bcrypt/Argon2 for password hashing. MD5 was designed by Ronald Rivest in 1991 to replace the earlier MD4 hash function. It processes input data in 512-bit blocks and produces a fixed 128-bit output regardless of input size. While MD5 was once widely used for security purposes, cryptographic weaknesses discovered in 2004 and later make it unsuitable for security-sensitive applications. However, it remains useful for non-cryptographic purposes like checksums and data deduplication.
Key Characteristics
- Produces a fixed 128-bit (32 hexadecimal characters) output
- Deterministic - same input always produces same output
- Fast computation suitable for large files
- One-way function - cannot reverse hash to original data
- Collision vulnerabilities discovered - not secure for cryptographic use
- Still widely used for checksums and file verification
Common Use Cases
- File integrity verification and checksums
- Detecting duplicate files in storage systems
- Generating unique identifiers for caching
- Verifying downloaded file integrity
- Legacy password storage (not recommended for new systems)
Example
Loading code...Frequently Asked Questions
Is MD5 still safe to use for password hashing?
No, MD5 is not safe for password hashing. It is cryptographically broken and vulnerable to collision attacks. For password hashing, use modern algorithms like bcrypt, Argon2, or PBKDF2 which are specifically designed to be slow and resistant to brute-force attacks.
What is the difference between MD5 and SHA-256?
MD5 produces a 128-bit hash (32 hex characters) while SHA-256 produces a 256-bit hash (64 hex characters). SHA-256 is cryptographically secure and recommended for security applications, whereas MD5 has known vulnerabilities and should only be used for non-security purposes like checksums.
Can an MD5 hash be reversed to get the original data?
No, MD5 is a one-way hash function and cannot be mathematically reversed. However, attackers can use rainbow tables or brute-force methods to find inputs that produce the same hash, which is why MD5 is no longer secure for cryptographic purposes.
Why do different files sometimes have the same MD5 hash?
This is called a collision, where two different inputs produce the same hash output. MD5's 128-bit output space and discovered vulnerabilities make it possible to deliberately create collisions. This is a major security flaw that makes MD5 unsuitable for verifying file authenticity.
What are valid use cases for MD5 today?
MD5 is still acceptable for non-security purposes such as file integrity checksums (when not concerned about malicious tampering), cache key generation, data deduplication, and generating unique identifiers. For any security-sensitive application, use SHA-256 or SHA-3 instead.