Ssh which key

Connect with SSH. Troubleshooting SSH. Verify commit signatures. Troubleshoot verification. Checking for existing SSH keys. Note: GitHub is improving security by dropping older, insecure key types. Did this doc help you? Help us make these docs great!

Make a contribution Or, learn how to contribute. SSH uses a pair of keys to initiate a secure handshake between remote parties. The key pair contains a public and private key. The private vs public nomenclature can be confusing as they are both called keys. It is more helpful to think of the public key as a "lock" and the private key as the "key".

You give the public 'lock' to remote parties to encrypt or 'lock' data. This data is then opened with the 'private' key which you hold in a secure place. At a very high level SSH keys are generated through a mathematical formula that takes 2 prime numbers and a random seed variable to output the public and private key.

This is a one-way formula that ensures the public key can be derived from the private key but the private key cannot be derived from the public key. SSH keys are created using a key generation tool. The SSH command line tool suite includes a keygen tool. Most git hosting providers offer guides on how to create an SSH Key. Both OsX and Linux operating systems have comprehensive modern terminal applications that ship with the SSH suite installed.

The process for creating an SSH key is the same between them. You will then be prompted to "Enter a file in which to save the key. The next prompt will ask for a secure passphrase. If someone gains access to the computer that private keys are stored on, they could also gain access to any system that uses that key. Adding a passphrase to keys will prevent this scenario.

The ssh-agent is another program that is part of the SSH toolsuite. The ssh-agent is responsible for holding private keys. Think of it like a keychain. In addition to holding private keys it also brokers requests to sign SSH requests with the private keys so that private keys are never passed around unsecurly.

Before adding the new SSH key to the ssh-agent first ensure the ssh-agent is running by executing:. Windows environments do not have a standard default unix shell.

What is important to note is the use of a randomly generated number, m , is used with signing a message along with a private key, k. This number m must be kept private. More in this later. Algorithms using elliptic curves are also based on the assumption that there is no generally efficient solution to solving a discrete log problem.

The computational complexity of the discrete log problem allows both classes of algorithms to achieve the same level of security as RSA with significantly smaller keys. Performance Larger keys require more time to generate. First published in , RSA has the widest support across all SSH clients and languages and has truly stood the test of time as a reliable key generation method.

According to NIST standards, achieving bit security requires a key with length bits whereas other algorithms use smaller keys. Bit security measures the number of trials required to brute-force a key.

This number m must be kept privately. The value m is meant to be a nonce, which is a unique value included in many cryptographic protocols. However, the additional conditions of unpredictability and secrecy makes the nonce more akin to a key, and therefore extremely important. Not only is it difficult to ensure true randomness within a machine, but improper implementation can break encryption. For example:. In other words, the class reused some randomly generated numbers.

This exposed a number of different Android-based Bitcoin wallets to having their private keys stolen. The requirements of the nonce m means that any two instances with the same nonce value could be reverse engineered and reveal the private key used to sign transactions. Taking this a step further, fail0verflow discovered the private key used to sign firmware updates for the Sony Playstation 3.

In other words, programmers could write their own code, sign it with the revealed private key, and run it on the PS3. As it turns out, Sony was using the same random number to sign each message. Every other week we'll send a newsletter with the latest cybersecurity news and Teleport updates.

The two examples above are not entirely sincere. In response to the desired speeds of elliptic curves and the undesired security risks, another class of curves has gained some notoriety. While offering slight advantages in speed over ECDSA, its popularity comes from an improvement in security. Instead of relying on a random number for the nonce value, EdDSA generates a nonce deterministically as a hash making it collision resistant.

Taking a step back, the use of elliptic curves does not automatically guarantee some level of security. Not all curves are the same. Only a few curves have made it past rigorous testing. Put together that makes the public-key signature algorithm, Ed Peter Ruppel puts the answer succinctly:.

Because here we are considering a signature for authentication within an SSH session.