如何从 SSH 私钥中检索公钥？

Question

生成的 SSH 私钥ssh-keygen包含公钥部分。如何从私钥中检索此公钥？我丢失了我的公钥，需要将此公钥的内容放在服务器authorized_keys文件中，并且不想创建新的密钥对。

或者说：如何id_rsa.pub从id_rsa文件创建文件？

Answer 1

我在 Server Fault: Create a public SSH key from the private key上找到了答案？

该选项-y输出公钥：

ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub

作为旁注，公钥的注释丢失了。我有一个需要评论的网站（Launchpad？），所以您需要编辑~/.ssh/id_rsa.pub评论并将评论附加到第一行，评论和关键数据之间有一个空格。下面显示了一个示例公钥。

ssh-rsa AAAA..../VqDjtS5 ubuntu@ubuntu

对于添加到 SSH 代理的密钥（在后台运行并避免需要一遍又一遍地重新输入密钥文件密码的程序），您可以使用该ssh-add -L命令列出添加到的密钥的公钥代理（通过ssh-add -l）。当 SSH 密钥存储在智能卡上（并且无法访问私钥文件）时，这很有用。

Answer 2

This is a solution is specifically for users using Windows to SSH into their remote machines, including cloud images on Amazon AWS and GCE.

(Disclaimer)

I recently used this solution to remote log in to new deployed VM images on GCE.

Tools used:

1. puttygen
2. WinSCP

Steps to perform:

1. Generate a public/private key pair using puttygen.
2. Upload a public key to your server in the cloud or remote location.

Description (how to do it):

1. Generate a key/pair or use an existing private key:

   If you have a private key:

   Open puttygen, press load button and select your private key (*.pem) file.

   If you do not have a private key:

   • Open puttygen,
   • Select the desired key type SSH2 DSA (you may use RSA or DSA) within the Parameters section... and it is important that you leave the passphrase field blank,
   • Press generate and follow instructions to generate (public/private) key pair.

   

2. Create a new 'authorized_keys' file (with Notepad):

   Copy your public key data from the "Public key for pasting into OpenSSH authorized_keys file" section of the PuTTY Key Generator, and paste the key data to the "authorized_keys" file.

   Make sure there is only one line of text in this file.

3. Upload the key to a Linux server:

   • Open WinSCP,
   • Select the SFTP file protocol and log in with your SSH credentials.
   • On success, you see the home directory structure at your remote machine.

   Upload authorized_keys file to the home directory at the remote machine.

4. Set proper permissions:

   Make a .ssh directory (if it does not exist)

   Copy the authorized_keys file to the .ssh directory (this will replace any existing authorized_keys file; take note of this).

   If the file exists, simply add the contents of this file to the existing file.

   Run commands to set permissions:

    sudo chmod 700 .ssh && chmod 600 .ssh/authorized_keys
   

Now you will be able to ssh into a remote machine without entering credentials every time.

Further reading:

1. Generating and uploading SSH keys under Windows

2. Authentication without password using OpenSSH Key, certificates .pem and .pub