Blockchain is a technology that allows data to be protected from manipulation. So, in this sense, it improves data security. Simply put, this security is achieved by making the records saved in the blockchain transparent and immutable, which is accomplished by redundantly and distributed storing each record at multiple nodes across a large network. When we consider the requirements of the EU General Data Protection Regulation (GDPR), the very essence of blockchain security is in conflict with the privacy required for personal data protection. As a result, the development of a blockchain project must include a careful examination of the type of data being stored and whether that data can be compromised. 
 
5 Security Issues in Blockchain 

Many people are correct in believing that blockchain is inherently secure. Blockchain is undeniably beneficial to businesses but has significant drawbacks due to specific security concerns. Here are the top five blockchain security challenges and their solutions. 

 51% Attacks 

Miners play an important role in validating blockchain transactions, allowing them to grow even further. A 51% attack is possibly the most feared threat in the blockchain industry. These attacks are more likely in the early stages of the chain, and a 51% attack does not apply to enterprise or private blockchains. 

To prevent 51% attacks: 

1. Increase the monitoring of mining pools. 
2. Ensure that the hash rate is higher. 
3. Avoid using consensus procedures based on proof-of-work (PoW). 

Phishing Attacks 

Phishing attacks on blockchain networks are becoming more common, causing severe problems. Phishing attempts frequently target individuals or company employees.  
 
The hacker aims to steal the user’s credentials in a phishing attack. They have the ability to send legitimate-looking emails to the owner of the wallet key. The user must enter login information via an attached bogus hyperlink. Access to a user’s credentials and other sensitive information could cause harm to both the user and the blockchain network. 

To prevent Phishing Attacks 

1. Increase browser security by installing a trusted add-on that alerts you to dangerous websites. 
2. Boost device security by installing malicious link detection software as well as trustworthy antivirus software. 
3. If you receive an email requesting login information related to the issue, reconfirm with the partner. 
4. Don’t click on the link until you’ve read it thoroughly. Enter the address into your browser instead of clicking on the links. 
5. Avoid using open Wi-Fi networks when using an electronic wallet or performing other critical banking transactions. 
6. Check to see if your system and software are up to date.  

Routing Attacks 

Routing attacks are the primary concern for blockchain technology’s security and privacy.  
 
The real-time movement of massive amounts of data is essential to a blockchain network and application. Hackers can use the anonymity of an account to intercept data as it is transmitted to internet service providers. 

To avoid routing attacks: 

1. Use secure routing protocols (with certificates).  
2. Encrypt your data. 
3. Change passwords on a regular basis, and use strong passwords.  

Sybil Attacks 

In a Sybil attack, hackers create a large number of bogus network nodes. The hacker can obtain majority consensus and disrupt the chain’s transactions by using those nodes. As a result, a large-scale Sybil assault is essentially a 51% attack. 

To prevent Sybil Attacks 

1. Use suitable consensus algorithms.  
2. Keep an eye on the behavior of other nodes and look for nodes that are only forwarding blocks from one user.  

While these algorithms may not completely prevent these attacks, they do make the hacker’s execution impossible. 

With the onset of blockchain-based services and products, service providers must make sure that they look at every day as an end day and make sure to treat all kinds of threats with the best possible solution there is.