Security and Cryptography in Linux
EGLUG session presented by – Amr Ali

Key points
What the word “hacker” means?
●
● Cryptography? You mean the username/password thing?
● Security is NOT Cryptography.
● Is there a security mindset?
● I'm not a gov agency, why should I care about security?
● Security through obscurity? Pffft .. yeah right.
● Linux way of applying security measures and practical
cryptography.

A hacker
Hacker (noun): Is an intelligent, talented, and
innovative person that have a combination of
skills that allows him/her to bring innovation to
reality.
A hacker could be, an inventor, a programmer
(mainly), a systems engineer, or anyone that could
think outside of the box and bring ideas and
solutions that are not present.

Cryptography, what?
Cryptography is not the username/password fields, this is called authentication,
in the other hand, cryptography is thee art of encryption, which turns plain text to
cipher text.
/* Authentication */
Username: Alice
Password: ******
/* Cryptography (Encryption) */
“I'm welling to pay you the agreed amount of money which is $2000.” --->
“AB76CD5E9F0F77D6A55E2A....”
As we can see encryption something really we don't see on daily bases if not at
all, because most of the time it is implemented to be transparent to the user.

Security is not cryptography!
Cryptography is a security field, not security it self.
A cryptographer: is a person that makes (en/de)cryption
algorithms to be implemented into a certain manner.
A security engineer: is a person that implements cryptographic
algorithms into applications.
The strongest part of any security system is cryptography,
however implementation might have weaknesses.

Security Minds
Being a security engineer is really not just a title and a high salary
job with a pile of certifications. NO!
It takes dedication and hard work to “develop” security aware
mind, for example ....
A security engineer would think if he could ...
Shoplift at the mall while he's shopping, and how to exploit a
●
certain vulnerability in the system itself.
● Steal a car from the repair shop by knowing the car's owner last
name.
● Etc....

Security for everybody
Y'all might ask yourselves, why should I have
security measures in my company network or
home computer?
The answer is very simple, it is like giving out
your car's keys to a stranger, if you didn't protect
the key and the car, someone else going to make
use of them, and 99% of the time it is not going to
be in your best interest.

Security through obscurity
This security scheme of providing security by secrecy is proven to be
defunct for many reasons, despite the fact that it does not really make
your system any stronger, but rather weaker.
From an attacker point of view, if you are following this scheme, you are
basically making it harder to probe your system for security weaknesses,
however that exact measure gives a higher probability that there are
weaknesses in the system, which once found, your whole product
becomes vulnerable to that weakness and with time, exploitation is
inevitable.
The good way to go is to harden the security design itself so you don't
have to worry about reverse engineering, besides, it gives more
confidence to your future client, that he knows what exactly is happening.

The Linux Way
Linux gives us the freedom to apply cryptographic measures
without doing any coding at all. There are hundreds of tools
and resources Linux provides, we will have a look at them in
the following order ....
/dev/random & /dev/urandom
●
● aespipe, loop-aes and dm-crypt (weaker due to design)
● Sha1sum, sha256sum, sha512sum, md5sum (INSECURE)

/dev/random & /dev/urandom
/dev/random: is a TRNG or a True Random Number Generator, it uses
different sources as entropy (e.g hardware clocks, network traffic,
etc...). This character device provides very high level of entropy,
however if the internal pool got exhausted, it blocks until more
environmental noise is available.
/dev/urandom: (“unlocked” random) is a CSPRNG or a
Cryptographically Secure Pseudo Random Number Generator, the big
difference here is that it reuses the pool after it gets exhausted, which
in return a bit less entropy in the output than its counter part
/dev/random.

aespipe, loop-aes & dm-crypt
aespipe: I guess its name explains its function pretty well, but it is basically an
application that you could pipe through plain-text data and get cipher-text data as
output, which in result makes it a very good handy tool in your cryptographic
collection.
Examples:
~# echo “Cryptos are fun” | aespipe -e aes256 -H sha512
~# mkisofs -r /home/d4de | aespipe -e aes196 -T > image.iso
As we can see in the first example, we just simply encrypted the phrase “Cryptos
are fun” with AES256 cipher and hashed the key with SHA512, simple enough?
Now if you are going after encrypting an ISO image file and then burn it to a
blank CD, so you would be asked for a password to be able to mount the CD;
this one line in the second example should do it for you.

aespipe, loop-aes & dm-crypt
loop-aes: Is just your normal loop device except it provides
encryption/decryption with the use of AES ciphers. As we speak loop-aes have
patches for kernels up to 2.6.27, however if you are going to use the bleeding
edge 2.6.28, I'm afraid that you are going to patch your kernel like I did myself.
dm-crypt: This is a weak alternative to loop-aes for those who want easy setup
for their encrypted partitions, I said this is weak but not insecure because of the
fact that it is actually hard to mount an attack on its design flaw but still feasible.
The flaw is that dm-crypt stores key information and other arguments in the first
block in the encrypted disk or partition, which makes it possible to identify the
cipher used in the encryption process with the possibility of extracting more
information from it.
Personally I took the effort of manually patching my kernel for loop-aes.

shaXsum and md5sum
Some of you might have heard about hashes before, they are implemented in
many ways nowadays, but the most known ones are checking against a password
by storing the computed hash for the password and compare it to the provided
password's computed hash.
SHA Family is a suite-b NSA cryptographic hashing algorithms, which are
pretty good compared to MD5 which is made by RSA Labs.
Examples:
~# echo “Cryptos are fun” | sha1sum
~# sha256sum /home/d4de/somefile -b
I meant to not give an example for MD5, because as of december 2008 at CCC
conference, a practical collision attack mounted successfully which caused to
forge and validate intermediate SSL certificates, in result most if not all CA's
changed their hash algorithms to SHA or some strong equivalent.

Final words
Please remember the following points ...
(1) A hacker is not a cracker.
(2) Security mindset is something you need to develop, not to “purchase”.
(3) Cryptography is NOT Security.
(4) A strong cryptographic cipher weakly implemented makes your “security”
vulnerable, but that does NOT mean that the cipher is weak.
(5) Hire a thief to teach you how to protect your car, do NOT hire a cop.
This presentation will be available at my website at (http://amr-ali.co.cc).

Security and Cryptography in Linux
EGLUG session presented by – Amr Ali

Key points
What the word “hacker” means?
●
Cryptography? You mean the username/password thing?
●
● Security is NOT Cryptography.
● Is there a security mindset?
● I'm not a gov agency, why should I care about security?
● Security through obscurity? Pffft .. yeah right.
● Linux way of applying security measures and practical
cryptography.

A hacker
Hacker (noun): Is an intelligent, talented, and
innovative person that have a combination of
skills that allows him/her to bring innovation to
reality.
A hacker could be, an inventor, a programmer
(mainly), a systems engineer, or anyone that could
think outside of the box and bring ideas and
solutions that are not present.

Cryptography, what?
Cryptography is not the username/password fields, this is called authentication,
in the other hand, cryptography is thee art of encryption, which turns plain text to
cipher text.
/* Authentication */
Username: Alice
Password: ******
/* Cryptography (Encryption) */
“I'm welling to pay you the agreed amount of money which is $2000.” --->
“AB76CD5E9F0F77D6A55E2A....”
As we can see encryption something really we don't see on daily bases if not at
all, because most of the time it is implemented to be transparent to the user.

Security is not cryptography!
Cryptography is a security field, not security it self.
A cryptographer: is a person that makes (en/de)cryption
algorithms to be implemented into a certain manner.
A security engineer: is a person that implements cryptographic
algorithms into applications.
The strongest part of any security system is cryptography,
however implementation might have weaknesses.

Security Minds
Being a security engineer is really not just a title and a high salary
job with a pile of certifications. NO!
It takes dedication and hard work to “develop” security aware
mind, for example ....
A security engineer would think if he could ...
Shoplift at the mall while he's shopping, and how to exploit a
●
certain vulnerability in the system itself.
● Steal a car from the repair shop by knowing the car's owner last
name.
● Etc....

Security for everybody
Y'all might ask yourselves, why should I have
security measures in my company network or
home computer?
The answer is very simple, it is like giving out
your car's keys to a stranger, if you didn't protect
the key and the car, someone else going to make
use of them, and 99% of the time it is not going to
be in your best interest.

Security through obscurity
This security scheme of providing security by secrecy is proven to be
defunct for many reasons, despite the fact that it does not really make
your system any stronger, but rather weaker.
From an attacker point of view, if you are following this scheme, you are
basically making it harder to probe your system for security weaknesses,
however that exact measure gives a higher probability that there are
weaknesses in the system, which once found, your whole product
becomes vulnerable to that weakness and with time, exploitation is
inevitable.
The good way to go is to harden the security design itself so you don't
have to worry about reverse engineering, besides, it gives more
confidence to your future client, that he knows what exactly is happening.

The Linux Way
Linux gives us the freedom to apply cryptographic measures
without doing any coding at all. There are hundreds of tools
and resources Linux provides, we will have a look at them in
the following order ....
/dev/random & /dev/urandom
●
aespipe, loop-aes and dm-crypt (weaker due to design)
●
● Sha1sum, sha256sum, sha512sum, md5sum (INSECURE)

/dev/random & /dev/urandom
/dev/random: is a TRNG or a True Random Number Generator, it uses
different sources as entropy (e.g hardware clocks, network traffic,
etc...). This character device provides very high level of entropy,
however if the internal pool got exhausted, it blocks until more
environmental noise is available.
/dev/urandom: (“unlocked” random) is a CSPRNG or a
Cryptographically Secure Pseudo Random Number Generator, the big
difference here is that it reuses the pool after it gets exhausted, which
in return a bit less entropy in the output than its counter part
/dev/random.

aespipe, loop-aes & dm-crypt
aespipe: I guess its name explains its function pretty well, but it is basically an
application that you could pipe through plain-text data and get cipher-text data as
output, which in result makes it a very good handy tool in your cryptographic
collection.
Examples:
~# echo “Cryptos are fun” | aespipe -e aes256 -H sha512
~# mkisofs -r /home/d4de | aespipe -e aes196 -T > image.iso
As we can see in the first example, we just simply encrypted the phrase “Cryptos
are fun” with AES256 cipher and hashed the key with SHA512, simple enough?
Now if you are going after encrypting an ISO image file and then burn it to a
blank CD, so you would be asked for a password to be able to mount the CD;
this one line in the second example should do it for you.

aespipe, loop-aes & dm-crypt
loop-aes: Is just your normal loop device except it provides
encryption/decryption with the use of AES ciphers. As we speak loop-aes have
patches for kernels up to 2.6.27, however if you are going to use the bleeding
edge 2.6.28, I'm afraid that you are going to patch your kernel like I did myself.
dm-crypt: This is a weak alternative to loop-aes for those who want easy setup
for their encrypted partitions, I said this is weak but not insecure because of the
fact that it is actually hard to mount an attack on its design flaw but still feasible.
The flaw is that dm-crypt stores key information and other arguments in the first
block in the encrypted disk or partition, which makes it possible to identify the
cipher used in the encryption process with the possibility of extracting more
information from it.
Personally I took the effort of manually patching my kernel for loop-aes.

shaXsum and md5sum
Some of you might have heard about hashes before, they are implemented in
many ways nowadays, but the most known ones are checking against a password
by storing the computed hash for the password and compare it to the provided
password's computed hash.
SHA Family is a suite-b NSA cryptographic hashing algorithms, which are
pretty good compared to MD5 which is made by RSA Labs.
Examples:
~# echo “Cryptos are fun” | sha1sum
~# sha256sum /home/d4de/somefile -b
I meant to not give an example for MD5, because as of december 2008 at CCC
conference, a practical collision attack mounted successfully which caused to
forge and validate intermediate SSL certificates, in result most if not all CA's
changed their hash algorithms to SHA or some strong equivalent.

Final words
Please remember the following points ...
(1) A hacker is not a cracker.
(2) Security mindset is something you need to develop, not to “purchase”.
(3) Cryptography is NOT Security.
(4) A strong cryptographic cipher weakly implemented makes your “security”
vulnerable, but that does NOT mean that the cipher is weak.
(5) Hire a thief to teach you how to protect your car, do NOT hire a cop.
This presentation will be available at my website at (http://amr-ali.co.cc).