Hashing is a cornerstone of modern cryptography, serving as a mechanism to transform data into a fixed-size string of characters, which is typically a digest that represents the original data. In the context of databases like MySQL, hashing is primarily used for password storage and authentication. The core objectives of cryptographic hashing include:

• Integrity: Ensuring that data has not been tampered with.
• Authentication: Verifying user credentials without storing plaintext passwords.
• Non-reversibility: Making it computationally infeasible to retrieve the original input from its hash.

A robust hash algorithm is expected to resist collision attacks, pre-image attacks, and rainbow table attacks. For more details on cryptographic hash functions, refer to NIST’s glossary.

The MySQL 5 hash algorithm was introduced as part of MySQL 4.1 and became the default in MySQL 5.x series. Its development was driven by the need to address the security shortcomings of earlier versions, which used a less secure, custom hash function. The new algorithm aimed to provide stronger protection against password cracking and unauthorized access.

The shift to the MySQL 5 hash algorithm marked a significant step forward in the database’s security model, aligning it more closely with established cryptographic standards of the time. However, as cryptographic research advanced, the limitations of this algorithm became more apparent, prompting further evolution in subsequent MySQL releases.

Prior to MySQL 4.1, the database used a proprietary 16-byte hash function for password storage, which was vulnerable to various attacks due to its simplicity and lack of cryptographic rigor. The MySQL 5 hash algorithm replaced this with a 41-character hexadecimal string derived from the SHA-1 hash function, significantly increasing resistance to brute-force and dictionary attacks.

For a detailed history of MySQL authentication, see MySQL documentation on password hashing.

The MySQL 5 hash algorithm is fundamentally based on the SHA-1 cryptographic hash function. SHA-1, standardized by NIST in FIPS PUB 180-1, produces a 160-bit (20-byte) hash value. In MySQL 5, password hashes are stored as a 41-character string: an asterisk (*) followed by 40 hexadecimal digits representing the SHA-1 digest.

The hashing process involves a double application of SHA-1:

hash = SHA1(SHA1(password))

This double hashing was intended to provide additional security by making pre-computation attacks more difficult. For further background on the SHA-1 hash function and its cryptographic implications, see SHA-1: Insights into Its Security and Applications.

The process for generating a password hash in MySQL 5 is as follows:

1. The plaintext password is hashed using SHA-1.
2. The resulting hash is hashed again with SHA-1.
3. The final hash is stored as a 41-character string: an asterisk (*) followed by the 40-character hexadecimal SHA-1 digest.

Example:

Input password: secret123
Step 1: SHA1('secret123') = 84d961568a65073a3bcf0eb216b2a576c206d8ba
Step 2: SHA1(84d961568a65073a3bcf0eb216b2a576c206d8ba) = 2c1743a391305fbf367df8e4f069f9f9a44f979f
Stored hash: *2C1743A391305FBF367DF8E4F069F9F9A44F979F

This output format is easily recognizable and is used internally by MySQL for authentication.

The MySQL 5 hash algorithm is implemented in the server’s authentication system. When a user attempts to log in, the following steps occur:

• The client sends a hashed version of the password (using a challenge-response protocol) to avoid transmitting the plaintext password over the network.
• The server retrieves the stored hash from the mysql.user table.
• The server verifies the hash using the same double-SHA1 process.

The relevant code can be found in the MySQL source tree, particularly in the sql/password.c file. For further technical details, see the MySQL Internals documentation.

While the MySQL 5 hash algorithm improved upon its predecessor, it is not immune to vulnerabilities:

• SHA-1 Weaknesses: SHA-1 is no longer considered secure against well-funded adversaries due to advances in collision attacks (CISA SHA-1 Deprecation Notice).
• Lack of Salting: The algorithm does not use a salt, making it susceptible to precomputed rainbow table attacks.
• Brute Force Attacks: The speed of SHA-1 allows attackers to attempt large numbers of guesses per second, especially with modern hardware.

These vulnerabilities have led to the algorithm being deprecated in favor of more secure alternatives. To understand the mechanics and modern limitations of SHA-1, visit SHA-1: Insights into Its Security and Applications.

The MySQL 5 hash algorithm offers moderate resistance to brute-force and dictionary attacks compared to its predecessor, but falls short by modern standards:

• Brute Force: Without salting or computational cost factors, SHA-1 hashes can be brute-forced relatively quickly using GPUs or ASICs.
• Rainbow Tables: The absence of a salt means attackers can use precomputed tables to reverse hashes for common passwords.
• Collision Attacks: While less relevant for password hashing than for digital signatures, the theoretical possibility of SHA-1 collisions further undermines trust in the algorithm.

For current best practices in password hashing, refer to OWASP Password Storage Cheat Sheet. If you're interested in the impact of hardware advancements on password cracking, see GPU Password Cracking Benchmarks 2025: RTX vs CPUs.

Modern password hashing algorithms such as bcrypt, PBKDF2, scrypt, and Argon2 offer significant security improvements over the MySQL 5 hash algorithm:

• Salting: Modern algorithms use unique salts for each password, thwarting rainbow table attacks.
• Key Stretching: They introduce computational cost, making brute-force attacks much more expensive.
• Stronger Hash Functions: Algorithms like SHA-256 or SHA-3 are used, which are more resistant to cryptanalysis.

For a comparative analysis, see CIS Password Hashing Guide. You can also explore a deep dive into the differences and strengths of modern hashing algorithms such as Argon2 and bcrypt.

The MySQL 5 hash algorithm was widely used for:

• User authentication in MySQL 5.x and earlier 5.6 deployments.
• Legacy applications that have not yet migrated to newer authentication plugins.
• Environments where backward compatibility with older clients or connectors is required.

Despite its limitations, the algorithm’s simplicity and ubiquity made it a default choice for many years.

The MySQL 5 hash algorithm has several critical limitations:

• No salt, making it vulnerable to rainbow tables.
• Based on SHA-1, which is deprecated by major standards bodies (ISO/IEC 10118-3).
• Inadequate for compliance with modern security standards such as PCI DSS or GDPR.

As a result, MySQL has deprecated this algorithm in favor of more secure authentication plugins, such as caching_sha2_password and sha256_password, starting with MySQL 5.6 and 8.0. For official deprecation notices, see MySQL 8.0 Upgrade Guide.

Migrating away from the MySQL 5 hash algorithm is critical for several reasons:

• Security: Protect against modern attack vectors and comply with current best practices.
• Compliance: Meet regulatory requirements for data protection and password management.
• Support: Ensure compatibility with newer MySQL features and avoid deprecated functionality.

Failure to migrate can leave systems exposed to credential theft and regulatory penalties.

A secure migration from the MySQL 5 hash algorithm to a modern alternative involves several steps:

1. Assess Compatibility: Identify applications and clients that depend on the old authentication method.
2. Choose a Secure Plugin: Select caching_sha2_password or sha256_password for MySQL 8.0+, or integrate with external authentication systems.
3. Update User Passwords: Require users to reset their passwords, triggering re-hashing with the new algorithm.
4. Test Thoroughly: Validate authentication workflows in a staging environment before production rollout.
5. Monitor and Audit: Continuously monitor authentication logs and audit for legacy hash usage.

For a comprehensive migration guide, consult the MySQL 8.0 Upgrade Guide and CIS Controls for Databases.

The MySQL 5 hash algorithm represents a significant chapter in the evolution of database security, bridging the gap between insecure legacy methods and today’s robust cryptographic standards. While it offered improved security over its predecessors, its reliance on SHA-1 and lack of salting render it obsolete in the face of modern threats. Organizations are strongly encouraged to migrate to more secure authentication plugins and adopt best practices for password management. Staying informed about the cryptographic landscape is essential for safeguarding sensitive data and maintaining compliance in an ever-evolving threat environment.

• MySQL Documentation: Password Hashing in MySQL
• NIST: FIPS PUB 180-1 (SHA-1 Standard)
• CISA: SHA-1 Hash Function Deprecated
• OWASP: Password Storage Cheat Sheet
• CIS: Password Hashing – The Why and How
• MySQL 8.0 Upgrade Guide
• ISO/IEC 10118-3: Information technology — Security techniques — Hash-functions
• CIS Controls: Secure Configuration for Databases
• SHA-1: Insights into Its Security and Applications
• Unlocking the Strength of Argon2: The Future of Secure Hashing
• Understanding bcrypt: A Deep Dive into Its Mechanics and Usage in Cryptography
• GPU Password Cracking Benchmarks 2025: RTX vs CPUs