Every software developer has faced an issue at some point when pulling code from a repository. Git errors can occur due to several reasons, such as network issues, wrong configurations, or outdated software versions. But what if the error is related to the RSA key with SHA-1? In this blog post, we’ll look at a scenario with such an issue and walk through its resolution.


Let’s begin with a scenario. You’re working on your project and need to pull the latest code from your repository. You enter the standard command:

$ git pull

Unexpectedly, you’re faced with an error:

Warning: Permanently added the RSA host key for the IP address to the list of known hosts.
ERROR: You're using an RSA key with SHA-1, which is no longer allowed. Please use a newer client or a different key type.

Why did this happen, and how do we fix it? Let’s delve deeper.

Deciphering the Error

The error message tells us that the problem lies in the RSA key with SHA-1. RSA is a commonly used algorithm for public-key encryption, and SHA-1 is a widely used cryptographic hash function that produces a 160-bit hash value. GitHub has stopped supporting these keys due to security vulnerabilities. This blog post from GitHub explains more about the decision and the security reasons behind it.

The Attempt to Use the Ed25519 Key

Thinking the issue could be solved by using a different type of key, you attempt to generate a new key using the Ed25519 algorithm by running:

$ ssh-keygen -t ed25519

However, you’re met with another error: unknown key type ed25519. This suggests that your system doesn’t recognize or support the Ed25519 key type, which is a public-key signature system with several attractive features: small signatures, fast to compute, and resilience against various attacks. The problem here likely lies in the version of OpenSSH installed on your machine—it’s probably outdated and doesn’t support Ed25519.

The Solution

So how do you fix it? One option is to generate an ECDSA key with a 521-bit size. ECDSA stands for Elliptic Curve Digital Signature Algorithm. It’s an approach to public-key cryptography based on the algebraic structure of elliptic curves over finite fields. ECDSA offers the same level of security as RSA but with smaller keys, making it more efficient.

You generate an ECDSA key with a 521-bit size using the following command:

$ ssh-keygen -t ecdsa -b 521

Then, add the generated key to your deploy keys on GitHub with the following command:


This step is crucial to allow GitHub to recognize your new ECDSA key.

In summary, the error occurred due to GitHub’s decision to stop supporting RSA keys with SHA-1 due to security vulnerabilities, coupled with an outdated OpenSSH version that doesn’t support the Ed25519 key type. The problem was resolved by generating a new ECDSA key with a 521-bit size and adding it to GitHub’s deploy keys.


Cryptographic algorithms and keys are an essential part of secure communication, but they can also be a source of confusion when they stop working. The key to understanding and resolving these errors is to decipher the error message, understand what’s causing it, and then determine the best course of action. In our case, updating our keys solved the issue.

Remember, staying updated with the changes in your development tools, including GitHub, is crucial for a smooth and secure development experience.

I hope this blog post helped you understand more about RSA keys, SHA-1, and how to deal with related errors. Keep learning, keep growing!