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SSH (Secure Shell) can be set up with public/private key pairs so that you don’t have to type the password each time. Because SSH is the transport for other services such as SCP (secure copy), SFTP (secure file transfer), and other services (CVS – Concurrent Versions System, etc), this can be very convenient and save you a lot of typing. While SSH2 can use either DSA or RSA keys, SSH1 cannot. SSH only does the authentication using RSA or DSA algorithm, the “rest” is encoded using a cipher (like IDEA, DES, Blowfish, etc, etc). SSH2 will also not use patented cypers like IDEA .
Here is how to generate the SSH Version 2 keys:
Create DSA or RSA key pair.
su@www:~$ ssh-keygen -t dsa Generating public/private dsa key pair. Enter file in which to save the key (/home/su/.ssh/id_dsa): Created directory '/home/su/.ssh'. Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/su/.ssh/id_dsa. Your public key has been saved in /home/su/.ssh/id_dsa.pub. The key fingerprint is: 1d:5d:00:55:73:39:0e:4b:75:3c:88:07:e5:98:67:6c su@www The key's randomart image is: +--[ DSA 1024]----+ | .+*+*o+| | o=* *o| | .o+E+ o| | . .+. . | | S . | | | | | | | | | +-----------------+
su@www:~$ ssh-keygen -t rsa -b 4096 Generating public/private rsa key pair. Enter file in which to save the key (/home/su/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/su/.ssh/id_rsa. Your public key has been saved in /home/su/.ssh/id_rsa.pub. The key fingerprint is: 80:f8:c6:c0:16:bb:52:f2:85:57:8a:97:9b:78:92:df su@www The key's randomart image is: +--[ RSA 4096]----+ | . . | | . * = | |. X B . | | = @ o . | |. * B S | | . = . | | . E | | | | | +-----------------+
When the key is generated, copy it to the target machine using either of the two commands:
ssh-copy-id email@example.com cat ~/.ssh/id_rsa.pub | ssh firstname.lastname@example.org "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
Where ‘user’ is the remote systems existing user and ‘220.127.116.11’ is the remote systems IP. The first command will copy all generated keys, but the second command must be run separately for each generated key.
DSA is faster in signing, but slower in verifying. A DSA key of the same strength as RSA (1024 bits) generates a smaller signature. A RSA 512 bit key has been cracked, but only a 280 DSA key. Also note that DSA can only be used for signing/verification, whereas RSA can be used for encryption/decrypt as well.
Create multiple keys and create ~/.ssh/config file:
Host server1 IdentityFile ~/.ssh/key_file1 Host server2 IdentityFile ~/.ssh/key_file2
sudo vim /etc/ssh/sshd_config #Find ChallengeResponseAuthentication and set to no: ChallengeResponseAuthentication no #Find PasswordAuthentication set to no PasswordAuthentication no #Find UsePAM and set to no: UsePAM no #Find PermitRootLogin and set to no: PermitRootLogin no
Q: I follow the exact steps, but ssh still ask me for my password!
A: Check your remote .ssh directory. It should have only your own read/write/access permission (octal 700) % chmod 700 ~/.ssh