# MD2

> obsolete cryptographic hash function

**Wikidata**: [Q741247](https://www.wikidata.org/wiki/Q741247)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/MD2_(hash_function))  
**Source**: https://4ort.xyz/entity/md2

## Summary

MD2 was established in 1989 . It is a thing defined by its establishment date and no other attributes are provided.

## Summary
MD2 is an obsolete cryptographic hash function designed by Ronald Rivest in 1989. It produces a 128-bit hash value and was one of the earliest message digest algorithms developed for cryptographic applications.

## Key Facts
- Created in 1989 by Ronald Rivest as a cryptographic hash function
- Produces a 128-bit (16-byte) hash value output
- Follows the Merkle-Damgård construction methodology
- Superseded by MD4 in 1990
- Described in RFC 1319: The MD2 Message-Digest Algorithm
- Has multiple ITU/ISO/IEC object identifiers including 1.2.840.113549.2.2
- Considered cryptographically broken and unsuitable for further use
- Available in 10 Wikipedia language editions including English, German, and Japanese

## FAQs
### Q: What is MD2 used for?
A: MD2 was originally used for cryptographic applications requiring data integrity verification and digital signatures. However, due to security vulnerabilities discovered over time, it is now considered obsolete and should not be used for any security-critical applications.

### Q: How does MD2 differ from MD5?
A: MD2 was developed before MD5 and produces the same 128-bit output size, but uses different internal operations and padding schemes. MD5 was designed to be faster than MD2 while maintaining similar security properties, though both are now considered cryptographically broken.

### Q: Is MD2 still secure to use?
A: No, MD2 is not secure for modern cryptographic applications. It has known vulnerabilities and collision attacks that make it unsuitable for any security-sensitive purposes. Modern alternatives like SHA-256 or SHA-3 should be used instead.

## Why It Matters
MD2 represents an important milestone in the evolution of cryptographic hash functions, demonstrating early approaches to creating secure message digests. As one of Ronald Rivest's first hash function designs, it helped establish foundational concepts in cryptographic engineering that influenced subsequent algorithms. While now obsolete, MD2's development process revealed critical insights about collision resistance, preimage resistance, and the importance of rigorous security analysis. The algorithm's eventual breaking also served as an important lesson in the field about the need for ongoing cryptanalysis and the temporary nature of cryptographic security. MD2's historical significance lies not in its current utility, but in its role as a stepping stone toward more robust cryptographic primitives that form the backbone of modern digital security infrastructure.

## Notable For
- One of the first practical cryptographic hash functions developed for widespread use
- Introduced the concept of message padding to ensure fixed-length input blocks
- Demonstrated early applications of the Merkle-Damgård construction in hash functions
- Served as a direct predecessor to the more successful MD4 and MD5 algorithms
- Documented in one of the earliest RFCs dedicated to cryptographic hash functions

## Body
### Technical Specifications
MD2 operates on 8-bit bytes and produces a 128-bit hash value. The algorithm processes input messages in 16-byte blocks, padding the final block if necessary to reach this length. It uses a 48-byte auxiliary block during computation and performs 18 rounds of processing per 16-byte block.

### Security Properties and Vulnerabilities
The algorithm was designed to be collision-resistant and preimage-resistant, though these properties were compromised through cryptanalysis over time. Research in the 1990s and 2000s demonstrated practical collision attacks, making MD2 unsuitable for any security applications. The birthday paradox attack complexity is significantly lower than the ideal 2^64 operations for a 128-bit hash.

### Historical Context
MD2 was developed during a period of rapid advancement in public-key cryptography and digital signatures. It was created to provide a standardized way to generate fixed-size digests from arbitrary-length messages, enabling efficient signature schemes and data integrity verification. The algorithm's design reflects the computational constraints and security understanding of the late 1980s.

### Implementation Details
The algorithm uses addition modulo 256 and XOR operations throughout its rounds. It employs a static permutation table for non-linear mixing and includes a checksum calculation as part of the final hash computation. These design choices, while innovative at the time, contributed to the algorithm's eventual vulnerabilities.

## References

1. Freebase Data Dumps. 2013