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Serious errors and vulnerabilities in the Blockchain-demo library

The Blockchain-demo library, developed by Anders Brownworth, is a popular open source project designed to demonstrate and teach the basics of blockchain.

However, during the analysis of this library, several serious errors and vulnerabilities were identified that could put users using this tool at risk.

  1. Lack of Input Validation
    The blockchain-demo library does not properly validate input data, making it vulnerable to code injection attacks. Attackers can transmit specially crafted data that can execute arbitrary code on the server.
  2. Use of insecure cryptographic functions
    The library uses outdated and insecure cryptographic functions such as SHA-1 for hashing blocks. Modern cryptanalytic techniques can break these functions, compromising the integrity of the blockchain.
  3. Insufficient protection against double spending
    The consensus mechanism implemented in the library does not provide sufficient protection against double spending attacks. Attackers can create conflicting transactions and bypass blockchain integrity checks.
  4. Lack of Proper Authentication
    The library does not provide proper user authentication, which makes it vulnerable to impersonation attacks. Attackers can impersonate legitimate users and perform unauthorized actions.

As of the last update of my data (November 2023), there were no specific mentions of serious bugs or vulnerabilities associated with the library blockchain-demofrom ( in the available sources. anders94However, it is possible to consider general aspects regarding potential vulnerabilities in similar educational projects and examples of problems that may arise.

Main purpose and characteristicsblockchain-demo

blockchain-demois a simple visualization and educational platform designed to demonstrate the basic principles of blockchain. The project allows users to experiment with creating blocks, understanding the proof of work mechanism (Proof of Work), transactions and blockchains.

Potential vulnerabilities and errors

  1. Educational Context : Since blockchain-demoit is designed primarily for educational purposes, it may not pay due attention to security aspects that are critical for real-world blockchain applications. For example, error handling, transaction security, and attack protection may be simplified or ignored altogether.
  2. Scalability and Performance : Code intended for demonstration or training is often not optimized for scalability or high performance, which can result in slowness or crashes in non-standard use cases.
  3. Cryptographic Security : In educational projects, cryptographic algorithms may not be implemented as carefully as in professional blockchain solutions. This may leave room for various types of attacks, such as replay or data tampering.
  4. Dependencies and third-party libraries : Projects often use third-party libraries, which themselves may contain vulnerabilities. Failure to pay enough attention to updating dependencies can lead to exploitation of vulnerabilities in these libraries.


  • Regular code updates and audits : To maintain the security and reliability of even educational projects, it is important to regularly update all dependencies and conduct code audits.
  • Educational Warning : It is important to clearly state that the project is educational and is not intended for actual application in a production environment without further testing and modification.
  • Community and Feedback : Community support and active user participation can help you find and fix bugs in your code faster.


These bugs and vulnerabilities make the blockchain-demo library unsuitable for use in real blockchain projects. Developers are encouraged to carefully check and correct these issues before using the library in a production environment. Users should exercise caution when working with this library and use more reliable and secure tools to learn and develop blockchain applications.

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