Category Archives: Beginner

Slow wifi network on laptop

If network performance on your laptop is slow and unstable, it might be because power management of your wifi adapter and of Linux are not playing together. One of the things you will notice are flapping ping rates:

$ ping 192.168.0.1 
PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data.
64 bytes from 192.168.0.1: icmp_seq=1 ttl=64 time=23.3 ms
64 bytes from 192.168.0.1: icmp_seq=2 ttl=64 time=44.7 ms
64 bytes from 192.168.0.1: icmp_seq=3 ttl=64 time=1161 ms
64 bytes from 192.168.0.1: icmp_seq=4 ttl=64 time=35.2 ms
...
^C
--- 192.168.0.1 ping statistics ---
30 packets transmitted, 20 received, 33% packet loss, time 30000.14s
rtt min/avg/max/mdev = 23.3/537.9/2119.2/2005.3 ms

As you can see the 3rd ping has a high round trip time of over one second. You might also notice high packet loss rates.

If this is the case and your hardware seems to be ok, you can try to switch off Network Manager's automatic power management in /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf:

[connection] 
wifi.powersave = 2

Restart NetworkManager (sudo systemctl restart NetworkManager) or reboot your Laptop.

If you are not using NetworkManager, you can try to switch off power management directly:

sudo iwconfig wlp2s0 txpower fixed

Afterwards check that power management is really disabled:

sudo iwconfig wlp2s0
...
Power Management:off
...
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Security Alert: Migrate to Post-Quantum Cryptography Right Now!

Current cryptographic algorithms will be broken within the next couple of years:
https://www.zdnet.com/article/ibm-warns-of-instant-breaking-of-encryption-by-quantum-computers-move-your-data-today/

The time to migrate to post-quantum cryptography is right now. Ah yes ... and while you're at it, don't forget about crypto currency.

Migration steps towards post-quantum cryptography

  1. Identify possible technologies
  2. Choose algorithms for standardization
  3. Standardization (RFCs)
  4. Implementation
  5. Integration into operating systems

Right now, we are at step 1 and 2.

Update (20.04.2018):
OpenSSH 8.0 supports quantum-computing resistent key exchange method - still experimental though.
https://www.openssh.com/txt/release-8.0

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Android smartphone "Cubot Echo"

  • https://www.cubot.net/smartphones/echo/spec.html

Pros
+ Very good overall hardware quality compared to cheap price (unbreakable display, strong body for outdoor use)
+ Good display, camera quality and performance compared to cheap price
+ Large 5.0 inch display
+ HDR photography
+ Up to 128 GB micro sdcard, 16 GB ROM
+ Plain Android user experience, no annoying modifications or add-ons
+ Removable battery
+ Cheap price

Cons
- Android security patch level only from 05.06.2017, but latest firmware update (which will be installed automatically after setup) DOES include security patch for WiFi WPA2 KRACK attack (build 08.02.2018). Android 6 Marshmallow does no longer receive security updates from Google, but you can install the unofficial Android alternative LineageOS based on Android 7 Nougat.
- No 4G / LTE support
- A bit heavy

Verdict
You can get this Android smartphone for as cheap as 60 EUR. If you can live with the security issues and the missing LTE support, that's a definitive buy. Especially considering that the upcoming Google Pixel 3 flagship for 850 EUR guarantees Android security updates for only 3 years. You could buy 14 Cubot Echos for that price. And the Google Pixel 3 does not have a removable battery, which makes it very hard to replace.

Cubot EchoCubot J5
Android VersionAndroid 6 Marshmallow
(no longer supported)
Unofficial support for LineageOS
based on Android 7 Nougat
Android 9
ProcessorMT6580 1.3 GHz Quad-coreMT6580 1.3 GHz Quad-core
Display5" IPS
(1300:1 contrast)
5.5"
(18:9 format, 1300:1 contrast)
Brightness (cd/㎡)450450
Memory (RAM / ROM)2 GB / 16 GB2 GB / 16 GB
Max. Additional Storageup to 128 GB (not included)up to 128 GB (not included)
Camera (Back / Front)13 MP / 5 MP8 MP / 5 MP (interpolated)
LTEnono
ExtrasMicro + Standard Dual SIM, A-GPS, USB OTG, Special Sound Chip with Big Speaker, Unbreakable CaseDual Nano SIM, A-GPS, Gradient
Color Case
Battery3000 mAh (removable)2800 mAh (removable)
Price60 €65 €
Cubot NovaCubot Magic
Android VersionAndroid 8.1 OreoAndroid 7 Nougat
ProcessorMT6739 1.5 GHz Quad-coreMT6737 1.3 GHz Quad-core
Display5.5" HD+
(18:9 format, 1300:1 contrast)
5" IPS
(1300:1 contrast)
Brightness (cd/㎡)450450
Memory (RAM / ROM)3 GB / 16 GB3 GB / 16 GB
Max. Additional Storageup to 128 GB (not included)up to 128 GB (not included)
Camera (Back / Front)13 MP / 8 MP13 MP / 5 MP
(13 MP +2 MP Dual Back Camera)
LTEyesyes
ExtrasDual 4G Nano SIM, A-GPS,
Fingerprint Sensor
Dual Micro SIM and Dual Standby,
A-GPS, Curved Display Sides
Battery2800 mAh (removable)2600 mAh (removable)
Price70 €70 €

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Security Guidelines

Physical Device Security

  • Always completely switch off your computer and lock your computer safely away, even if you just visit the bathroom. Screen saver locking or putting the laptop into sleep mode is not enough (Cold Boot Attacks).
    https://blog.f-secure.com/cold-boot-attacks
  • Don't display anything important on your computer screen (Van-Eck-Phreaking).
    https://twitter.com/windyoona/status/1023503150618210304
    http://www.eweek.com/security/researchers-discover-computer-screens-emit-sounds-that-reveal-data
  • Don't type in anything important on your keyboard or touchscreen.
    http://www.eweek.com/security/researchers-discover-computer-screens-emit-sounds-that-reveal-data
  • Install USBGuard to protect against unknown USB devices.
    (Note that USB IDs and serial numbers of USB devices can easily be replicated. Once an attacker knows the type of USB device you are using, and its serial number, USBGuard can easily be bypassed. That means: Never lend someone your USB stick, never accept a USB device from untrustworthy persons ... which means anyone.)

Software Security

  • Always use fingerprints to identify certificates for important web services. Don't rely solely on CAs.
    https://www.theregister.co.uk/2018/09/06/certificate_authority_dns_validation/

Useful Links

  • Ubuntu Security
    https://www.ubuntu.com/security
  • Ubuntu Security Features Matrix
    https://wiki.ubuntu.com/Security/Features
  • End User Device Security Guidance for Ubuntu 18.04 LTS from the National Security Center (a part of GCHQ)
    https://www.ncsc.gov.uk/guidance/eud-security-guidance-ubuntu-1804-lts
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Password security - it is not about length or complexity

Passwörter sollten nach Möglichkeit nicht im Klartext am Bildschirm angezeigt werden. Neben dem offensichtlichen Shoulder Surfing ("über die Schulter schauen"), gibt es auch sog. Seitenkanalangriffe in blickgeschützten Bereichen.

Das ursprünglich für ältere Röhrenmonitore entwickelte Van-Eck-Phreaking, bei dem die elektromagnetische Strahlung über größere Distanzen aufgezeichnet wird, lässt sich offenbar auch für moderne LCD-Monitore mit HDMI-Kabel ausnutzen. Aus der empfangenen elektromagnetischen Strahlung wird dann das ursprüngliche Monitorbild rekonstruiert. Die dazu notwendige Elektronik ist mittlerweile schon für ambitionierte Hobby-Bastler erschwinglich.

Einige Quellen im Internet weisen ebenso auf relativ hohe elektromagetische Strahlungen und akustische Signale von aktuellen PC-Grafikkarten und Flachbildschirmen/Touchscreens in Kombination mit Monitor- und Stromkabeln hin, die im Prinzip wie eine Antenne funktionieren.

Um Sicherheitsproblemen in diesem Bereich von vornherein aus dem Weg zu gehen, kann man z.B. moderne Passwortmanager verwenden, die Passwörter automatisch generieren und dann über die Zwischenablage in die Anwendung kopieren, ohne das Passwort selbst im Klartext eintippen oder auf dem Bildschirm anzeigen zu müssen.

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Sending mail on the Linux command line (Ubuntu 18.04)

How to send end-to-end encrypted emails on the Linux command line.

If you want to add attachments, use mutt or mail from GNU Mailutils as the mail client. The following examples use mailx and ssmtp.

Unencrypted mail

Install package "bsd-mailx":

$ sudo apt-get install bsd-mailx

Edit /etc/mail.rc and add the following lines:

set smtp=smtp://mail.example.com
alias root postmaster@example.com

Run mailx:

$ mailx root
Subject: test 
This is a test. 
. 
Cc: 

Notes:

  • Mail gets sent to postmaster@example.com (see mail.rc).
  • Mail server is mail.example.com (see mail.rc).
  • Email message body is terminated by a single "." as the last line.

Encrypted mail (Inline PGP)

Make sure you can send unencrypted mail (s. "Unencrypted mail" above).

Check that you have GnuPG version 2 installed, and If you haven't done so before, create private and public GnuPG key.

$ gpg --version
gpg (GnuPG) 2.2.4
libgcrypt 1.8.1
...
$ gpg --gen-key
...

Import public PGP key from recipient.

$ gpg --import alice.pub

First sign message (clearsign - ascii signature will be appended to text), then encrypt message, then mail message.

$ echo "Hello Alice, if you can read this your PGP mail client is working." | \
    gpg --clearsign | \
    gpg -a -r alice@example.com --encrypt | \
    mailx -s "PGP encrypted mail test" alice@example.com

Notes:

  • First sign the message. "gpg --clearsign" uses the default private key to sign message. Check with "gpg -K". Otherwise use option "--default-key bob@example.com" to choose a specific private key.
  • Then encrypt the message. Check with "gpg -k" that recipient is properly added to your GPG keyring.
  • Finally send mail message. Email body is simply the signed and encrypted message text in ASCII format.
  • Email subject will not be encrypted.

Encrypted mail (S/MIME)

Make sure you can send unencrypted mail (s. "Unencrypted mail" above).

You need your own public certificate / private key pair, and the public certificate from the recipient (all in PEM format).

You can get a S/MIME email certificate for free from COMODO. Or you run your own certificate authority. Either way, both your own certificate and your own key need to be in a single file in PEM format (in the following example it is called "bob.pem").

-----BEGIN PRIVATE KEY-----
 ...
-----END PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
 ...
-----END CERTIFICATE-----

The public certificate of the recipient must be in PEM format too (in the following example it is called "alice.pem"). You can extract it from an email signature if the recipient already sent you a signed email.

-----BEGIN CERTIFICATE-----
 ...
-----END CERTIFICATE-----

Install the package "ssmtp".

$ sudo apt-get install ssmtp

Again (as in the above example for PGP encrypted mail), all commands for signing, encrypting and sending the message can be chained together to a single command line.

$ echo "Hello Alice, if you can read this your S/MIME mail client is working." | \
    openssl smime -sign -signer bob.pem -text | \
    openssl smime -encrypt -from bob.example.com -to alice@example.com -subject "S/MIME encrypted mail test" -aes-256-cbc alice.pem | \
    ssmtp -t

Notes:

  • Email body is simply the signed and encrypted message text in ASCII format. OpenSSL adds all required headers to it (sender, recipient, subject).
  • If you are using a S/MIME certificate from a public CA (like COMODO) to sign your message, it is easier for the recipient to validate your signature, compared to PGP encrypted emails.
  • You still need the public certificate of the recipient, and make somehow sure that it is authentic.
  • Again, the email subject will not be encrypted.
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Check for new versions of Firefox, Thunderbird

#!/bin/bash 
 
function checkVersion() { 
        V1=$(echo $1 | tr -d [:alpha:])
        V2=$(echo $2 | tr -d [:alpha:])
        MAJ1=$(echo $V1 | cut -d. -f1) 
        MIN1=$(echo $V1 | cut -d. -f2) 
        REV1=$(echo $V1 | cut -d. -f3) 
 
        MAJ2=$(echo $V2 | cut -d. -f1) 
        MIN2=$(echo $V2 | cut -d. -f2) 
        REV2=$(echo $V2 | cut -d. -f3) 
 
        if [[ $MAJ1 -lt $MAJ2 ]] ; then 
                return 1; 
        fi 
 
        if [[ $MAJ1 -eq $MAJ2 ]] ; then 
                if [[ -n "$MIN2" ]] ; then 
                        if [[ -n "$MIN1" ]] ; then 
                                if [[ $MIN1 -lt $MIN2 ]] ; then 
                                        return 1; 
                                fi 
 
                                if [[ $MIN1 -eq $MIN2 ]] ; then 
                                        if [[ -n "$REV2" ]] ; then 
                                                if [[ -n "$REV1" ]] ; then 
                                                        if [[ $REV1 -lt $REV2 ]] ; then 
                                                                return 1; 
                                                        fi 
                                                else 
                                                        return 1; 
                                                fi 
                                        fi 
                                fi 
                        else 
                                return 1; 
                        fi 
                fi 
        fi 
 
        return 0; 
} 
 
# Check Thunderbird 
TB=$(curl -s https://ftp.mozilla.org/pub/thunderbird/releases/ | sed -n "s/^\s\+<td><a href=\".*\">\(.*\)\/<\/a><\/td>$/\1/gp" | sort -g | egrep -iv "b|esr" | tail -n 1 ) 
TBL=$(thunderbird -v | sed -n "s/^\s*Thunderbird\s*\(.*\)$/\1/gp") 
 
checkVersion $TBL $TB 
if [[ $? -eq 1 ]] ; then 
        echo "Update Thunderbird ($TBL -> $TB)" 
fi 
 
# Check Firefox 
TB=$(curl -s https://ftp.mozilla.org/pub/firefox/releases/ | sed -n "s/^\s\+<td><a href=\".*\">\(.*\)\/<\/a><\/td>$/\1/gp" | sort -g | egrep -iv "b|esr" | tail -n 1 ) 
TBL=$(firefox -v | sed -n "s/^.*Firefox\s*\(.*\)$/\1/gp") 
 
checkVersion $TBL $TB 
if [[ $? -eq 1 ]] ; then 
        echo "Update Firefox ($TBL -> $TB)" 
fi

Settings in about:config for built-in update check:

  • app.update.interval
  • app.update.url
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That was 2017

Ubuntu 16.04 LTS Security Notices

Overall USNs: 348

Highest CVE priority fixed by USN:

  • High: 61
  • Medium: 277
  • Low: 5

Bugfixes in Red Hat Enterprise Linux 7

https://www.redhat.com/security/data/metrics/

Critical: 45 vulnerabilities
** Average time for fixing: 2 days
** 15% were 0day
** 37% were within 1 day
** 100% were within 7 days
** 100% were within 14 days
** 100% were within 31 days
** 100% were within 90 days

Important: 137 vulnerabilities
**Average time for fixing: 39 days
** 22% were 0day
** 29% were within 1 day
** 63% were within 7 days
** 65% were within 14 days
** 69% were within 31 days
** 87% were within 90 days

Moderate: 308 vulnerabilities
**Average time for fixing: 165 days
** 3% were 0day
** 8% were within 1 day
** 20% were within 7 days
** 21% were within 14 days
** 25% were within 31 days
** 43% were within 90 days

Low: 103 vulnerabilities
**Average time for fixing: 264 days
** 0% were 0day
** 2% were within 1 day
** 7% were within 7 days
** 7% were within 14 days
** 7% were within 31 days
** 19% were within 90 days

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Top 20 reasons for choosing weak passwords

  1. You just don't care because the account does not contain sensitive data and you are not using your real name anyway.
  2. Typing in strong passwords with a combination of special characters and regular characters takes ages on smart phones and tablets.
  3. Computers can't be trusted anyway, so why bother with a complicated password?
  4. Nobody is interested in you anyway.
  5. Password is for a shared account. Explaining to someone the password "%&__!(E2-<"+?=-:*d3//#@" over the phone is just too nerve wrecking.
  6. You want to have access to the account in case of an emergency, and you are afraid to forget the password if it is too complicated.
  7. "12345" can not be so bad if everyone else is using it as a password.
  8. After using strong passwords for years, your wifi was hacked by a 13 year old neighbor kid who got bored playing World of Warcraft on a Saturday evening.
  9. When creating an account you first choose a password easy to remember, only to change it later to a much more secure password. Never happens.
  10. The real password is your username.
  11. You are a math genius: If "12345" is so highly likely to be guessed, why do these numbers never get picked by the national lottery?
  12. Two words: Quantum computers
  13. Passwords are for pussies: Secret information is hidden in porn movies using steganography.
  14. You are a celebrity who wants to get into the headlines.
  15. You want to become a celebrity and therefore use every way to get into the headlines.
  16. Wife wants to set a trap for her husband to see if he is spying on her. Chooses a weak password and checks login times regularly.
  17. What was the question? Passwords? ... yeah ... do you know where my skateboard is?
  18. You know that "12345" is not secure, but at least it's more secure than "1234".
  19. The account is only a temporary account. You use it once and then forget about it.
  20. The account was automatically created by a script.
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