openssl/ssh-keygen

openssl

(Note: Not work on Git Bash Windows: it will hangs and doesn't respond)

Generate RSA private key: M_E.key
$ openssl genrsa -des3 -out M_E.key 2048
Generating RSA private key, 2048 bit long modulus
..........+++
..........................+++
e is 65537 (0x10001)
Enter pass phrase for M_E.key: Set pass phrase for private key
Verifying - Enter pass phrase for M_E.key:

Generate RSA public key: M_E.pub
$ openssl rsa -in M_E.key -pubout > M_E.pub
Enter pass phrase for M_E.key: Input pass phrase
writing RSA key

Use public key(M_E.pub) to encrypt
$ echo 'Hello World!'|openssl rsautl -encrypt -pubin -inkey M_E.pub > cipher.txt
Use Private Key(M_E.key) to decrypt
$ cat cipher.txt | openssl rsautl -decrypt -inkey M_E.key
Enter pass phrase for M_E.key: input pass phrase
Hello World!
    

ssh-keygen

Generate RSA private key and public key
$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/c/Users/Admin/.ssh/id_rsa): ./M_E_KEY 
Enter passphrase (empty for no passphrase): Set pass phrase
Enter same passphrase again:
Your identification has been saved in ./M_E_KEY.
Your public key has been saved in ./M_E_KEY.pub.
The key fingerprint is: ...
The key's randomart image is: ...

Convert ssh public key to PEM format(that 'openssl rsautl' can read it)
$ ssh-keygen -f M_E_KEY.pub -e -m PKCS8 > M_E_KEY.pem

$ echo 'Hello World!' > plain.txt
Use public key(M_E_KEY.pem) to encrypt
$ openssl rsautl -encrypt -pubin -inkey M_E_KEY.pem -ssl -in plain.txt -out cipher.txt   
Another way
$ echo 'Hello World!' | openssl rsautl -encrypt -pubin -inkey M_E_KEY.pem > cipher.txt

$ cat cipher.txt
|▒pL▒▒▒8▒▒T+▒*▒Bu▒2▒▒]j...

Use private key(M_E_KEY) to decrypt
$ cat cipher.txt | openssl rsautl -decrypt -inkey M_E_KEY
Hello World!
Another way
$ openssl rsautl -decrypt -inkey M_E_KEY -in cipher.txt
Hello World!
Save result to decryptedMessage.txt
$ openssl rsautl -decrypt -inkey M_E_KEY -in cipher.txt -out decryptedMessage.txt
Another way
$ openssl rsautl -decrypt -inkey M_E_KEY -in cipher.txt > decryptedMessage.txt

SSH LOGIN By RSA KEY

Send public key(id_rsa.pub) to /home/user/.ssh/authorized_keys of the host(authorized_keys file will automatic create if it not exist)
$ ssh-copy-id user@host
Send specified publick key to the host
$ ssh-copy-id -i ./M_E_KEY.pub  user@host

Logined to user@host
$ sudo vim /etc/ssh/sshd_config
Modify：
PubkeyAuthentication  yes                      # Enable PublicKey authentication
AuthorizedKeysFile       .ssh/authorized_keys  # Public key path
PasswordAuthentication  no

ssh Login
$ ssh -i ~/.ssh/id_rsa user@host
or
$ ssh user@host (default: -i ~/.ssh/id_rsa)