Copy SSH Keys to Server with SFTP

These steps assume you already have a public SSH key, if not, create one

SSH-Copy-Id is an easier way to upload ssh keys, however, it does not work on all devices.

ssh to the remote server using your password.

If it is not already created, create the authorized_keys file under the .ssh folder

touch ~/.ssh/authorized_keys

chmod 600 ~/.ssh/authorized_keys

vi ~/.ssh/authorized_keys

Add your public key to the end of the authorized_keys file

Ensure that the correct owner and permissions are on the files.

The .ssh directory should be

chmod 700 .ssh

And the authorized_keys file should be 600

chmod 600 ~/.ssh/authorized_keys

Both should be owned by the user. Change username to your username.

sudo chown -R username:username .ssh/authorized_keys

Helpful links

https://blog.tinned-software.net/setup-sftp-only-account-using-openssh-and-ssh-key/

https://blog.tinned-software.net/ssh-passwordless-login-with-ssh-key/

How to install Armory Wallet on Fedora? – Notes

At the moment it does not look easily possible to install Armory Wallet on Fedora. Here are some notes about trying to get it to work.

The following person on Reddit was able to get it working on an older version of Fedora.

[Tutorial] Install Armory Wallet 0.96.4 on Fedora Workstation 29
byu/AmbitiousSpeed0 inBitcoin

The issue is that pyqt4 and pyqt4-devel are not available on the latest versions of Fedora.

The following prerequisites need to be installed

sudo dnf install git nano qt qt-devel python-devel libtool lmdb swig python-psutil

Other notes.

Armory relies on Bitcoin Core. You can install BitCoin core from https://bitcoincore.org. It will need to be fully synced which can take a long time “as in days/weeks”. Note that Armory will not work if you have the blockchain pruned. Which means you’ll need about 500GB of space for the BitCoin blockchain.

https://github.com/goatpig/BitcoinArmory

List of Symmetric Encryption Algorithms. Block and Key Size.

List of common symmetric encryption algorithms with their block and key size.

NameBlock SizeKey SizeNotes
AES Advanced Encryption Standard128128, 192, 256Is Rijndael
RijndaelVariable128, 192, 256Is AES
Blowfish 6432-448Often used in SSH
DES Data Encryption Standard6456
Triple DES64112-168DES 3 times
IDEA64128Used in PGP
RC4 Rivest Cipher 4Stream Cipher40-2048Insecure/Not used, used in WEP, WPA, and SSL
RC5 Rivest Cipher 532, 64, 1280-2040
RC6 Rivest Cipher 6128128, 192, 256
Skipjack6480Developed by the NSA and supported key escrow
CAST-1286440-128
CAST-256128128, 160, 192, 224, 256
Twofish1281-256
ChaCha20Stream Cipher256
List of Common Symmetric Encryption Algorithms With Block and Key Size

Import/Export GPG Private Key

Note that if you need to copy both your Private and Public key, you’ll need to export both separately.

https://stackoverflow.com/questions/5587513/how-to-export-private-secret-asc-key-to-decrypt-gpg-files

List Keys

You can list all the GPG keys with the following command.

gpg --list-keys

Export Key

Change “keyID” to your key idea from the above command. The key ID is the long string of hexadecimal characters.

gpg --export-secret-keys "keyID" > private_key.asc

This will export the keys to private_key.asc. Rename as appropriate.

To export the Public Key

gpg --export "keyID" > public_key.asc

Import Key

To use the key, you’ll need to import and trust the key.

gpg --allow-secret-key-import --import private_key.asc
gpg --edit-key "keyID"

Then type

trust

Select level 5.

Import the Public Key

gpg --import public_key.asc

Decrypt Files

To decrypt a single file do

 gpg --batch --passphrase='password' ./file.gpg

If your GPG does not have a password, remove the whole `–passphrase=’password’` option

To decrypt multiple files you can run

for file in * ; do gpg --batch --passphrase='password' "$file" ; done

How To Check if RHEL/AlmaLinux needs a reboot after an update

Typically you’ll need to reboot a server after an update if the Linux Kernel was updated. It is possible that services need to be restarted.

There is some good information here https://serverfault.com/questions/122178/how-can-i-check-from-the-command-line-if-a-reboot-is-required-on-rhel-or-centos

Using Yum Utilities needs-restarting

Install the needs-restarting utility

sudo dnf install -y yum-utils

Once installed, we can check if we need to reboot with

sudo needs-restarting -r

The -r option only reports if a reboot is required.

If we wanted to automatically check and reboot, we could do

sudo needs-restarting -r || sudo shutdown -r

Alternative way

We could alternatively just check the kernel version and if it is different, manually reboot the machine. Note that there could be a couple cases where the kernel didn’t update, but you still need a reboot, or services needed to be restarted View links below for more information.

LAST_KERNEL=$(rpm -q --last kernel | perl -pe 's/^kernel-(\S+).*/$1/' | head -1)
CURRENT_KERNEL=$(uname -r)

test $LAST_KERNEL = $CURRENT_KERNEL || shutdown -r

View Fiber SFP details in Mikoritk RouterOS

Quick and simple way to check the details on a fiber SFP on a Mikrotik router. Replace sfp1_name with the SFP name or leave out the name and select a number.

/interface ethernet monitor "sfp1_name"

Results

                      name: sfp1
                    status: link-ok
          auto-negotiation: done
               full-duplex: yes
           tx-flow-control: no
           rx-flow-control: no
               advertising: 
  link-partner-advertising: 
        sfp-module-present: yes
               sfp-rx-loss: no
                  sfp-type: SFP-or-SFP+
        sfp-connector-type: LC
       sfp-link-length-9um: 3000m
           sfp-vendor-name: UBNT
    sfp-vendor-part-number: UF-SM-1G-S
         sfp-vendor-serial: FL31F80285729
    sfp-manufacturing-date: 20-02-20
            sfp-wavelength: 1550.32nm
           sfp-temperature: 64C
        sfp-supply-voltage: 3.23V
       sfp-tx-bias-current: 30mA
              sfp-tx-power: -5.254dBm
              sfp-rx-power: -4.1dBm
           eeprom-checksum: good
                    eeprom: 0000: 01 02 03 00 00 00 00 00  00 00 00 .....

How to determine if Ubuntu Needs a Reboot after an update

Typically after a Linux Kernel update, you will want to reboot your machine to take advantage of the new kernel. But how do you know if you need to reboot?

Fortunately, there is a simple way to check.

cat /var/run/reboot-required

If it returns

*** System restart required ***

Then we should reboot the machine.

https://www.cyberciti.biz/faq/how-to-find-out-if-my-ubuntudebian-linux-server-needs-a-reboot/

Using Auditd to monitor changes to Linux

Install and enable auditd with

sudo dnf install auditd
sudo systemctl enable auditd
sudo systemctl start auditd

Add a file or directory to monitor with

auditctl -w /etc/passwd -k password

-w is watch path
-k is a filter key we can use later to search through logs

Now we can search with ausearch

ausearch -k password

Using Preconfigured Rules

There are already some preconfigured rules in /usr/share/audit/sample-rules/

We can copy those to /etc/auditd/rules.d/ and use them.

cd /usr/share/audit/sample-rules/
cp 10-base-config.rules 30-stig.rules 31-privileged.rules 99-finalize.rules /etc/audit/rules.d/
augenrules --load

Note on the 31-privileged.rules file. You’ll need to run the commands in the file which will create a new file. Then we can copy that to “/etc/auditd/rules.d/”

find /bin -type f -perm -04000 2>/dev/null | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $1 }' > priv.rules
#find /sbin -type f -perm -04000 2>/dev/null | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $1 }' >> priv.rules
#find /usr/bin -type f -perm -04000 2>/dev/null | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $1 }' >> priv.rules
#find /usr/sbin -type f -perm -04000 2>/dev/null | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $1 }' >> priv.rules
#filecap /bin 2>/dev/null | sed '1d' | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $2 }' >> priv.rules
#filecap /sbin 2>/dev/null | sed '1d' | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $2 }' >> priv.rules
#filecap /usr/bin 2>/dev/null | sed '1d' | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $2 }' >> priv.rules
#filecap /usr/sbin 2>/dev/null | sed '1d' | awk '{ printf "-a always,exit -F path=%s -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged\n", $2 }' >> priv.rules

And Copy priv.rules to /etc/audit/rules.d/31-privileged.rules. Overwrite the file there if needed.

cp ./priv.rules /etc/audit/rules.d/31-privileged.rules

Load the rules.

augenrules --load

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/security_hardening/auditing-the-system_security-hardening

DNS Query “sl 0.0.0.0” in Mikrotik DNS Cache

Sounds like this could be from a potential scan. The record is useless as 0.0.0.0 doesn’t go to anything.

https://learn.microsoft.com/en-us/answers/questions/547092/what-is-the-sl(0)-in-dns-logs-as-host-name

We can block this type of behavior by blocking inbound DNS request. Change in-interface to your interface or change to an interface list.

ip firewall filter add chain=input protocol=6 dst-port=53 in-interface=ether1 action=drop
ip firewall filter add chain=input protocol=17 dst-port=53 in-interface=ether1 action=drop

How to Create a Self Signed TLS Certificate in Linux

Here is a quick way to create a self signed certificate in Linux.

Run the following command. Fill out the required info.

openssl req -x509 -sha256 -nodes -days 3652 -newkey rsa:4096 -keyout /etc/pki/tls/private/localhost.key -out /etc/pki/tls/certs/localhost.crt
chmod 400 /etc/pki/tls/private/localhost.key

Now in your Apache or Nginx files, specify the path to the Key and the Certificate.

Note that if you’ll need to add the

https://www.linode.com/docs/guides/create-a-self-signed-tls-certificate/