rihemebh/security-cheat-sheet

Security

• 0. Before we start
• 1. Attacks
• 2. Firewalls
• 2. Encryption
  • 2.1 Symmetric Encryption
    • 2.1.0 Feistel
  • 2.2 Asymmetric Encryption
    • 2.2.0 Needham-Schroeder
    • 2.2.1 RSA
    • 2.2.2 ELGamal
  • 2.3 Hybrid Encryption
    • 3.3.1 Diffie Hellman (DH)
• 3. Hash
• 4. Kerberos
• 5. Elliptic Curve
• 6. OpenSSL

Before we start

Some important notions

name	description
Identification	Who are you ?
Authentication	Prove it
Authorization	Do you have the right to do something ?
Audit	What did you do ?
FootPrint	Recognition
Integrity	Ensuring that information cannot be changed
Confidentiality	Ensuring that information can be accessed (read) only by authorized persons
DLP	Discret Logarithm Problem : finding the number y where x = g^y mod, g is given and p is a large prime number

Frequently used CMDs

gpg : is the cmd for encryption

• Get Hostname

hostname -I

• Connect remotely via a private network

ssh <username>@<hostname>

• Secure copy :

scp <filename> <username>@<hostname>:<path>

Attacks

Attack	Description	Example
Birthday Attack	It is made against the Hash algorithms. (Belongs to a class of brute force) All hashed messages have a fixed length (independent from the input length) and they unique for that message. this attack refers to the probability of finding two random messages m1 and m2 that has the same Hash h(m1) = h(m2) so the attacker can safely replace the message by his own one	What is the relation with the birthday: Since we have a finite number of days in one year (365) there is a big chance to have 2 persons with the same birthday in a finite number of persons.
Password attack	Trying to guess the password or having a databse of passwords called dictionnary	- Brute Force : using a random approach by trying different passwords and hoping that one work Some logic can be applied by trying passwords related to the person’s name, job title, hobbies or similar items. - Dictionary attack: dictionary of common passwords is used to attempt to gain access to a user’s computer and network. One approach is to copy an encrypted file that contains the passwords, apply the same encryption to a dictionary of commonly used passwords, and compare the results.
Man in the middle	occurs when a hacker inserts itself between the communications of a client and a server	Session hijacking
SQL Injection	SQL commands are inserted into data-plane input (for example, instead of the login or password) in order to run predefined SQL commands	“SELECT * FROM users WHERE account = ‘’ or ‘1’ = ‘1’;” Because ‘1’ = ‘1’ always evaluates to TRUE, the database will return the data for all users instead of just a single user.
Cross-site scripting (XSS)	Use third-party web resources to run scripts in the victim’s web browser or scriptable application
Ransomware	Ransomware is a type of malware from cryptovirology that threatens to publish the victim's personal data or perpetually block access to it unless a ransom is paid. While some simple ransomware may lock the system without damaging any files, more advanced malware uses a technique called cryptoviral extortion.

Firewalls

The major role of firewalls is:

• Intercepting incoming traffic between network and trust levels
• Authorizing or reject access
• Enabling a more secure connection to open networks
• Audit network usage

Netfilter

Netfilter is a Linux kernel module that provides the ability to monitor, modify and filter IP packets, and track connections. It thus provides firewall functions, Internet connection sharing and network traffic authorization.

IpTables

IpTable in a CMD interface to configure Netfilter

Commands

The commands tells iptables what to do with the rest of the rule that is sent to the interpreter.

The chain's name : INPUT

• Rules' List

iptable -L --line-numbers

• Create a Chain (named allowed)

iptables -N allowed

• Erase a chain

iptables -X allowed

• Modify the authorization

iptables -P INPUT DROP

• Add rule to end of the chain

iptables -A INPUT

• Drop rule

iptables -D INPUT --dport 80 -j DROP, iptables -D INPUT 1

• Replace a rule

iptables -R INPUT 1 -s 192.168.0.1 -j DROP

• Insert a rule anywhere

iptables -I INPUT 1 --dport 80 -j ACCEPT

• Clear the chain's rules

iptables -F INPUT

• Reset thz chain's counters

iptables -Z INPUT

Encryption

Encryption is used to garantee Confidentiality

Symmetric Encryption

Use one shared encryption key between sender and receiver

• Encrypt the file :
  • Binary format (default)

    gpg -c <filename>
    

  • ASCII format

    gpg -c --armor(or -a) <filename>
    

• Get all the algos

 gpg --version 

Examples of symmetric algorithms:
AES (Advanced Encryption Standard), DES (Data Encryption Standard), IDEA (International Data Encryption Algorithm),RC4/5/6 (Rivest Cipher 4/5/6)

• Encrypt the file and specify the algo (cipher)

gpg -c -a --cipher-algo <filename>

• Decrypt

gpg -d <filename>

Advantages ++	Disadvantages --
Fast	non secure key
-	Large number of keys
-	Without signature

Feistel

• It's a a block cipher

Encryption algorithm:

1. The plain text is divided into 2 equal halves : G and D
2. The encryption function is applied on the right half D of the plaintext block. The result of this encryption function is then XORed with the left half G . The result of XOR function becomes the new right half R .

f : is the the encryption function that takes (data block) as input and returns one output of the same size as the data block.

Decryption Algorithm :

D = L and G = R XOR f(L)

Know that:
We could repeat this algo as many as we need if we want to increase the security.
The security also increases when the block is larger and the round function is more complex, but it may decrease the speed of encryption and decryption.

Asymmetric Encryption

Use public keys for encryption and private keys for decryption

• Generate Keys

gpg --full-generate-key
gpg --gen-key

• Get the Key List

gpg --list -keys

• Export a public key

gpg -o KEY -a --export <KeyID> 

• Import Key

gpg --import KEY

• Encryption

gpg -o file.enc -a -r <publicKey> -encrypt file

• Sign

gpg -o file.signed --sign-file

• Verify a signature

gpg --verify file.signed 

• Decrypt

gpg -o file --decrypt file.enc

Advantages ++	Disadvantages --
Secured	Slow
Signature
Less number of keys

Needham-Schroeder

Authentication Protocole

• pka : public key of na
• pkb : pyblic key of nb
• Na / Nb : random numbers

Algorithm: A wants to prove his identity to B

1. A sends his name and random number Na,this message is encrypted by an asymmetric encryption algorithmwith the public key of B (pkb ),
2. B decrypts the message with his private key
3. returns the random number generated by A (so A could make sure that the message is comming from B) and a new random number Nb : encrypted by the public Key of A
4. A receives the message and decrypt it with his private key
5. A sends Nb to B encrypted with pkb (to tell B that he successfully get his message)
6. Indentity proved !

Problem:

This algo could easly be attacked by the Man in the midlle

Solution:

• By adding b (prove the identity of b) , a will make sure if he is talking with b or with not

RSA

NP-complete problem

Parameters:

1. choose 2 prime numbers p & q
2. N= p*q
3. L = (p-1)*(q-1)
4. Generate the public Key (e,N): e is between 1 and L and coprime with N and L
5. private key (d,N) : d*e mod L =1

Encryption : mod N = C

Decryption : M = mod N

ELGamal

DLP : Discrete logarithm problem

Public Infos:
q : prime number
p = 2 q +1
Gq: cyclic group
g: generator of Gq

• Choose a private key X from Gq
• Public Key: y = g^X mod p

Encryption :

1. Choose a number k from Gq
2. u = g^k mod p
3. v = y^k M mod p ( M : message )
4. publish : (u,v)
   

Decryption:

1. D(u,v) = v/u^X = m

Hybrid Encryption

DH

p (prime number) and g are public infos

Algorithm: A and B want to communicate with each other by sharing the same Key

1. A chooses a random number "a" between 0 and p-1
2. B chooses a random number "b" between 0 and p-1
3. u = mod p (published by A) ; v= mod p (published by B)
4. Key of B : Kb= = mod p
5. Key of A : Ka= = mod p
   => Ka = Kb

Kerberos

it is responsible for authenticating, authorizing and monitoring users who want to access resources and services on your network. It acts as a watchdog against intruders on your network services.

Based on

• “Ticket” Granting

• Secret Key Cryptography

• Mutual authentication

• Time-limited tickets

• Anti-replay mechanisms

• It is based on 3 tiers architecture :

  • Client/user : Who wants to access a resource from the server
  • Ressources server : the machine that has resources
  • KDC: Key Distribution Center: Grant ticket for users allowed to access a service

Principal : Each user and service on the network is a principal.

Implementation : https://github.com/rihemebh/Kerberos-project

Elliptic Curve

ECC is based on the elliptic curve discrete logarithm problem, or (ECDLP), Instead of numbers, the elliptic curve’s problems operate on points, and multiplication is used instead of exponentiation : Finding the number k given a base point P where the point Q = kP.

ECC Auth:

The standard algorithm used for signing with ECC is ECDSA, which stands for elliptic curve digital signature algorithm. This algorithm has replaced RSA signatures and classical DSA signatures in many applications. It is, for example, the only signature algorithm used in Bitcoin and is supported by many TLS and SSH implementations.

Signature generation

Parameters:

n is the number of point in the curve

G = (x,y) is a base point

private key = d

public Key P = dG

Algorithm:

1. Hash a message (SHA-256 or BLAKE2) ⇒ generate h between 0 and n-1
2. Pick a random number k between 1 and n-1
3. compute kG
4. set r = x mod n
5. compute s = (h+rd)/ k mod n
6. signature = (r,s)

Signature Verification

1. compute w = 1/s = k / (h+rd) mod n
2. wh = hk(h+rd) = u
3. wr = rk(h+rd) = v
4. Q = uG + vP

The verifier only accepts the signature if the x coordinate of Q is equal to the value r from the signature.

Encryption

We have:

• (q ,G, G1, e), P un point de la CE E tq q divise p^k - 1
• n longueur du message
• H1 : (0, 1)* -> G*
• H2 : G1 -> (0, 1)^n
• PKG : calcule P pub = rP

Decryption

RSA VS ECC

Elliptic curve cryptography is often viewed as an alternative to RSA for public-key cryptography, but ECC and RSA don’t have much in common.

RSA is only used for encryption and signatures, whereas ECC is a family of algorithms that can be used to perform encryption, generate signatures, perform key agreement, and offer advanced cryptographic functionalities such as identity-based encryption.

The significant difference:

=> The same level of security with small numbers

ECC has two major advantages over RSA: shorter signatures and signing speed.

Because ECC works with shorter numbers, it produces shorter signatures than RSA (hundreds of bits long, not thousands of bits), which is an obvious benefit if you have to store or transmit numerous signatures.

Signing with ECDSA is also much faster than signing with RSA (though signature verification is about as fast) because ECDSA works with much smaller numbers than RSA does for a similar security level.

Reference : Serious Cryptography A Practical Introduction to Modern Encryption by --Jean-Philippe Aumasson

Hash

Hash is used to garantee Integrity : We use non-bijective functions to hash the message.
Whatever the size of the real message, the size of a hash message is always the same.
Examples of Hash functions : sha, sha256, md5

• Hash a file

$ asc25sum file
$ md5sum file
$ sha256sum file

OpenSSL

Definition

SSL (Secure Sockets Layer)

• Is an encryption-based protocol
• Ensure confidentiality,,Authentication and Integrity
• the predecessor of modern TLS(Transport Layer Security) encryption in use today

=> A website that implements SSL / TLS has an “HTTPS” in its URL instead of an “HTTP”.

OpenSSL is a software library for applications that secure communications over computer networks against eavesdropping or need to identify the party at the other end. It contains an open-source implementation of the SSL and TLS protocols. The core library, written in C programming language, implements basic cryptographic functions and provides various utility functions.

CMD

• Encrypt the "file" with "aes-128-cbc" algorithm and put the result in "file.enc"

openssl enc -aes-128-cbc -in file -out file.enc

// Apply the algoritm 2 times

openssl enc -aes-128-cbc -iter 2 -in file -out file.enc

• Decrypt

openssl enc -d -aes-128-cbc -in file.enc -out filerestored

openssl enc -d -aes-128-cbc  -iter 2 -in file.enc -out filerestored

• Generate RSA Key:

openssl genrsa -out mykey 2048

• Generate RSA params:

openssl rsa -in mykey -text -noout 

-noout : print the output in the terminal

• Generate a public key from a private key

openssl rsa -in mykey -pubout -out pub 

• Private Key Encryption :

openssl rsa -in mykey -des -out mykey.enc 

• Encrypt with public key

openssl rsault -encrypt -pubin -inkey PUB -in file -out file.enc 

• Decrypt

openssl rsautl -decrypt -inkey mykey.enc -in file -out rsa.enc 

Signature

• Sign with the private key

openssl rsault -sign -inkey myKey.enc -in file -out fileRSA.sign 

• Verify signature

openssl rsault -verify -pubin -inkey PUB -in fileRSA.sign

• Encrypt + Sign

openssl dgst -sha256 -verify PUB -signature fileHashSign file 

Certificate

• Digital Certificates are verifiable small data files that contain identity credentials to help websites, people, and devices represent their authentic online identity.

• Digital certificates cover three main uses:

  • Authentication: used to validate the identity of issuers as part of an authentication process, a crucial element of computer network security.
  • Signing: sed to sign a document or a file and to guarantee its integrity
  • Encryption: Garantee the security and integrity of information exchanged between a website and a browser, by means of a cryptographic key enabling a secure session to be activated (HTTPS protocol)

• Certification Authority issues digital certificates

---

• Get the Certification of the www.google.com website:

openssl s_client www.google.com:443

• Get the authority of a certification :
  google.cert is the file that contains google certification : output of the above cmd

openssl x509 -in google.cert -subject -issuer -noout

=> google trust

---

Goal:

• Create a certification authority called "INSAT"
• Create a certification for INSAT
• GL4 will ask a certification from INSAT
• INSAT will verify this request and generate a certificate
• Now INSAT is the authority of GL4

---

• Create RSA keys for INSAT and put it in INSAT.key

openssl genrsa -des3 -out INSAT.key 3072

• Create a certification for INSAT

openssl req -new -x509 -days 730 -key INSAT.key -out INSAT.cert

=> In this certificate INSAT is the subject and issuer : Self Signed Certificate

• Create keys for GL4

openssl genrsa -des3 -out gl4.key 3072

• Create request for a certiif from INSAT

openssl req -new  -key gl4.key -out gl4.req 

• Generate a Certificate for GL4:

openssl x509 -req -in gl4.req -out gl4.cert -CA INSAT.cert -CAKey INSAT.key -CAcreateserial -CAserial gl4.srl

• Export the certificate

openssl pkcs12 -export -out gl4.pfx -in gl4.cert -inkey gl4.key -name "certificat de gl4"

=> pkcs12 : put the certificate and the keys in the same file "gl4.pfx" so you can import it in the browser

• Import it

preference -> certificate manager -> my Certificates -> import

• Add Authority

preference -> certificate manager -> Authorities -> import -> choose INSAT.cert