CSE Module 04 - Encryption Hashing - EN PDF

 4 Encryption Wooclap time https://app.wooclap.com/events/SUYIDN Introduction Encryption  Encryption is the process of converting a plaintext message into a secure‐coded form of text, called ciphertext.  Decryption: The ciphertext cannot be understood without converting back...

 4 Encryption Wooclap time https://app.wooclap.com/events/SUYIDN Introduction Encryption  Encryption is the process of converting a plaintext message into a secure‐coded form of text, called ciphertext.  Decryption: The ciphertext cannot be understood without converting back via decryption—the reverse process from encryption—to plaintext.  The process uses a mathematical function which is controlled by a special password, called key (or keys). Introduction Encryption 1 2 3 4 5  Encryption is much older than cybersecurity 1 A B C D E 2 F G H I/J K  600 v.C: Spartans use a scytale 3 L M N O P  Atbash Cipher (600‐500 v.C.): 4 Q R S T U A simple substitution cipher used by Hebrew scholars. 5 V W X Y Z This involves replacing the first letter of the alphabet with the last, the second with the penultimate, etc.  Polybius Square (200 v.C.): A method developed by the Greek historian Polybius. It uses a 5x5 grid to encode letters into pairs of digits.  60 v.C.: Caesar uses a substitution encryption  WW I en II: Encryptie machines, b.v.de beroemde Enigma machine.  1979: The Kurt Schoenmaekers encryption Introduction Encryption  Encryption is in some countries heavily regulated. For instance, you cannot use certain algorithms or key lengths, and it is not always allowed to encrypt (specific) data. (China, Russia, India, Iran, US, UK, Australia, France).  Encryption is part of the science of CRYPTOGRAPHY.  Encryption is used to protect C and I, not A:  Protect “data at rest” on computers from unauthorized viewing and manipulation  Protect “data in transit” over networks from unauthorized interception and manipulation  Deter and detect accidental or intentional alterations of data  Verify authenticity of a transaction or document (see later: digital signature) Difference between Encoding and Encryption  Encoding transforms a message to another form. The algorithm to encode is always well‐known, reversible AND THERE IS NO KEY NEEDED. On the contrary, for encryption and decryption, you need a key.  For instance, when you convert a readable text to binary format (1’s and 0’s), it might seem unreadable, but it is not encrypted, just encoded as everybody can easily convert it back to readable text. E.g. Howest is encoded to binary: “01001000 01101111 01110111 01100101 01110011 01110100” but can easily be converted back. Online tools are available for instance here: https://codebeautify.org/string‐binary‐converter or Cyberchef.  Encryption nowadays relies on the secret of the key and not on the secrecy of the algorithm. (Caesar’s cipher is strictly speaking “Encoding” instead of “Encryption” as it was an algorithm only without key). Key elements of cryptographic (encryption) systems  Encryption algorithm ‐ Mathematically based function or calculation that encrypts or decrypts data.  Encryption key ‐ Piece of information similar to a password that makes the encryption or decryption process unique. A user needs the correct key to access or decipher a message, as the wrong key converts the message into an unreadable form.  Key length ‐ Predetermined length for the key. The longer the key, the more difficult it is to compromise in a brute force attack (where all possible key combinations are tried). So larger is better, but larger keys use more computation time => slower.  Plaintext – original message  Ciphertext – encrypted message Factors affecting the strength of a cryptographic system  Algorithm strength. Better public than secret as it then can be investigated and tested by many researchers.  Secrecy of the key and difficulty of compromising/finding an unknown key.  Nonexistence of back doors by which backdoors an encrypted file could be decrypted without knowing the key. Especially government‐sponsored algorithms are suspect.  Inability to decrypt parts of a ciphertext message by analyzing the patterns in the ciphertext.  Prevent known plaintext attacks.  Properties of the plaintext known by a perpetrator E.g. Letters often start with “Dear…” which is information that helps in deciphering letters. Two types of cryptographic systems  Symmetric key systems  Use single, secret, bidirectional keys that encrypt and decrypt.  Like in the physical world. You use the same key to close and reopen a door. Encrypt Decrypt Twee types van cryptographische systemen  Asymmetric key systems  Use a Pair (i.e., two) one‐way keys that are complementary to each other.  If one encrypts, only the other can decrypt and vice versa.  Usually one of these keys is kept secret (private key), and the other is made public (public key).  Can be compared to a mailbox where the opening is the “public” key and the key of the mailbox is the “private” key. Encrypt Decrypt Basic principles of symmetric encryption  Substitution Substitutes parts of the message with something else according a predefined algorithm. For instance, replace each character of the alphabet with the character that is three places to the right. A ‐> D, B ‐> E, etc. This was Caesar’s cipher (cipher = encryption algorithm)!  Transposition (or Permutation) Mixes the data by changing the places of blocks of data. A very simple transposition is to switch the places of every pair of characters. E.g. HOWEST ‐> OHEWTS. Transposition is the principle used by the Spartans for their encryption algorithm. The key is the thickness of the rod. Basic principles of (symmetric) encryption: SUBSTITUTION S U B S T I T U T I O N T V C T U J U V U J P O Key = 1 S U B S T I T U T I O N  Algorithm for encryption: Move places further in the alphabet  Algorithm for decryption: Move places back in the alphabet  Key : Number of places to move in the alphabet Basic principles of (symmetric) encryption: PERMUTATION Padding T R A N S P O S I T I O N T S I N R P T R A O I D N S O M Key = 4 T R A N S P O S I T I O N  Algorithm for encryption: Complete text with random characters until a multiple of. Move each character to a which is: (( ‐1) modulo ) * + ( modulo ). Or table.  Algorithm for decryption: = (( modulus ) ‐ 1) * + ( DIV ) + 1. Or table.  Key: Symmetric Encryption  Uses one and the same secret key to encrypt and decrypt. Sender side ‐ Alice Receiver side ‐ Bob Message Message Encrypt Ciphertext Ciphertext Decrypt (Plaintext) (Plaintext) Encrypt Decrypt Secure, separate (out‐of‐ band) key exchange Symmetric Encryption - Pros and Cons.  Advantages  Simple for the user as there is only one key to know for encryption and decryption.  Less complicated to use in cryptosystems than asymmetric encryption.  Faster and so use less computing power than asymmetric encryption.  SUITED FOR “BULK” ENCRYPTION, encryption of large quantities of data.  Disadvantages  Key distribution problematic. How to get the same key to two parties that may not even know each other in person?  Cannot be used for guaranteeing non‐repudiation (digital signatures) Stream ciphers and block ciphers  Stream Cipher  Encrypts data one bit or byte at a time.  Ideal for real‐time communication where data flows continuously, such as secure voice communications and real‐time video streaming.  Example: RC4  Block Cipher:  Encrypts data in fixed‐size blocks (e.g., 64 or 128 bits).  Suitable for Applications that manage blocks of data, such as file transfer, email, and database encryption.  Examples: AES, DES Voettekst 19 Modes of encryption  Electronic Codebook Each block of plaintext is encrypted independently using the same key.  Pros: Simple and fast.  Cons: Identical plaintext blocks result in identical ciphertext blocks, making it vulnerable to pattern analysis. Modes of encryption  Cipher Block Chaining (CBC) Each plaintext block is XORed with the previous ciphertext block before being encrypted. An initialization vector (IV) is used for the first block.  Pros: Provides better security than ECB by ensuring identical plaintext blocks produce different ciphertext blocks.  Cons: Requires an IV and is slower due to the dependency on previous blocks. Voettekst 21 Modes of encryption  Cipher Feedback (CFB) Converts a block cipher into a self‐synchronizing stream cipher. The previous ciphertext block is encrypted and then XORed with the plaintext block to produce the ciphertext.  Pros: Can encrypt data in units smaller than the block size.  Cons: Requires an IV and is slower due to the dependency on previous blocks. Voettekst 22 Modes of encryption  Output Feedback (OFB) Similar to CFB, but the output of the encryption function is fed back into the encryption process, not the ciphertext.  Pros: Converts a block cipher into a synchronous stream cipher, preventing error propagation.  Cons: Requires an IV and careful management to avoid repeating keystreams. Voettekst 23 Modes of encryption  Counter (CTR) Description: Converts a block cipher into a stream cipher by encrypting successive values of a counter and XORing with the plaintext.  Pros: Parallelizable, making it very fast and efficient.  Cons: Requires a unique counter value for each block to ensure security Voettekst 24 Some symmetric encryption algorithms  RC4 (Rivest Cipher 4)  Fast but obsolete.  Considered very weak, but unfortunately still used in some protocols as for example in WEP (WiFi Security Protocol).  DES (Data Encryption Standard)  Invented by IBM with the help of the NSA (National Security Agency)  64‐bit key (actually only 56, 8 used for parity check)  Encrypts blocks of 64 bit  Now considered weak and only used in Triple DES or 3DES where DES is used 3 times but the key is only twice as long (128 bits minus the parity bits). Some symmetric encryption algorithms  AES (Advanced Encryption Standard)  Successor to DES sought via public call for candidate algorithms by NIST.  Winners were two Belgians from KULeuven: Vincent Rijmen and Joan Daemen.  Method was originally called Rijndael.  128, 192 or 256‐bits key  Encrypts in blocks of 128 bits Rijndael can encrypt in blocks of 128 to 256 bits in 32‐bit increments.  Uses little memory, both in software and hardware.  Resists advanced attacks. Asymmetric Encryption  Uses two complementary keys. If one encrypts with one key, one can only decrypt with the other key. One key is always public, the other is always private and kept with the user. Sender side ‐ Alice Receiver side ‐ Bob Message Message Encrypt Ciphertext Ciphertext Decrypt (Plaintext) (Plaintext) Encrypt Decrypt Public Key Bob Private Key Bob Asymmetric Encryption  The private (or secret) key is kept as securely as possible by the owner (E.g. on a smart card).  The public key is published – often in a “phonebook” of sorts – so that everybody can use it.  Algorithms for asymmetric encryption are slower and use more computer power than symmetric algorithms.  Used for shorter messages => Asymmetric encryption often used for symmetric key distribution  Asymmetric encryption can be used for a digital signature. Key distribution using Asymmetric Encryption Sender side ‐ Alice Receiver side ‐ Bob Message Message Encrypt Ciphertext Ciphertext Decrypt (Plaintext) (Plaintext) Encrypted Encrypted Encrypt Symmetric Symmetric Decrypt Key Key Public Bob Private Bob Asymmetric Encryption for non-repudiation If the sender encrypts a message with his private key, anyone can decrypt it, but one is then sure that it came from the sender AND the sender cannot deny that he sent that message. A “digital signature,” in other words. Sender side ‐ Alice Receiver side ‐ Bob Message “Sign” “Verify” Message By Ciphertext Ciphertext By (Plaintext) Encrypting Decrypting (Plaintext) Secret Key Alice Public Key Alice Asymmetric Key Encryption – Some Standards  Most well‐known standard is RSA (Rivest, Shamir and Adleman)  Uses keys from 1,024 to 4,096 bit long typically.  Relies on the practical difficulty of factoring the product of two large prime numbers and uses modular arithmetic.  Computationally heavy. Often implemented in hardware. Asymmetric Key Encryption – Some Standards  Elliptical Curve Cryptography (ECC)  Less computational power needed than for RSA.  Based on the algebraic structure of elliptic curves over finite fields.  Allows for smaller keys than RSA with same security.  Hashing Voettekst 33 Hashing and hash  As asymmetric encryption is slow => it would take a long time to sign large documents or files.  A solution is to create a code which represents the document but is much shorter and encrypt this code with the secret key. The creation of such shorter code is called “hashing”. The code itself is called a hash code, hash value, digest or simply “hash”.  Requirements:  The hash must be easy and fast to compute  It must be very difficult to find two messages with the same hash. (Finding two messages with same hash is called a “collision”)  A hash code has a fixed length independent of the size of the input. Hashing and hash standards  MD5 (128 bit hash)  SHA‐1 (160 bit) Successed by SHA‐2 and SHA‐3 that get their hash length included in the name.  SHA‐256 (256 bit) or SHA3‐256  SHA‐512 (512 bit) or SHA3‐512  RIPEMD‐160 (160 bit), as well as RIPEMD‐256 and RIPEMD‐320  Hint: The length of the output hash gives a clue about the algorithm used! How does a hashing work? Simple example  A very simple way to hash :  Translate each character into a number (ASCII code).  Take per two numbers together to form a new number.  Add up all the numbers.  Then calculate the remainder when dividing by 99999 (modulo 99999).  Example: “Howest” Tekst H O w e s t ASCII 72 111 119 101 115 116 Per 2 72.111 119.101 115.116 Summed 306.328 Rest=HASH 6.331 Using a hash for a digital signature Message Message Hash Hash Function Function Sender side ‐ Alice Receiver side ‐ Bob Hash calculated Hash by Receiver =? “Sign” Signed Signed “Verify” Received calculated Encrypt Hash Hash Decrypt Hash by Sender Secret Key Alice Public Key Alice Digital Signature A digital signature ensures:  Data integrity Any change to the plaintext message would result in the recipient failing to compute the same hash.  Authentication The recipient can ensure that the message has been sent by the claimed sender since only the claimed sender has the secret key.  Non‐repudiation The claimed sender cannot later deny generating and sending the message as – again – he is the only one who possesses his secret key. The problem of key distribution Public Key Infrastructure (PKI)  Problem: How to guarantee that Alice’s public key is really from Alice, if Alice and Bob never meet? How does Alice get the key to Bob?  Solution: a Public Key Infrastucture where a “trusted party” (E.g. the government or a government‐appointed agency) guarantees that the public key is authentic and from Alice.  How does the trusted party guarantee this? By digitally signing the public key from a person with their secret key. Compare this to a passport where a government official signs your passport to proof that it is authentic.  The public key + information about its owner + the digital signature of the trusted party is put together in a DIGITAL CERTIFICATE. Public Key Infrastructure  Digital certificates of a user  This is a structured piece of text.  Contains the public key and identifying information about the user.  Signed by a trusted party with the trusted party’s private key.  Added to messages so that receiver can verify authenticity of the user’s public key by using the public key of the trusted party.  Contains at least:  A distinguishing (user)name  The user’s public key  The algorithm used to create the digital signature of the certificate by the trusted party  The validity period of the certificate Structuur van een digitaal certificaat (X.509) Version of X.509 Certificate Serial Number Certificate Algorithm Identifier for Certificate Issuer’s Signature Issuer Validity Period (From‐To) Subject Subject Public Identifier Algorithm Identifier (RSA, ECC, …) Public‐Key Value Issuer Unique Identifier Subject Unique Identifier Extensions (key usage, certificate policies, alternate subject names, …) Certification Authority’s Digital Signature Voettekst 42 Public Key Infrastructure (PKI) Certification Authority (CA) User Registration Authority (RA) Public Key Infrastructure  Certificate Authority (CA)  Authority in a network that issues and manages security credentials and public keys for message signature verification or encryption.  In order to generate a digital certificate, the CA gets/needs confirmation from a Registration Authority (RA) that the information provided by the user is correct.  => If the RA confirms the information provided by the user, the CA creates the content of the digital certificate and signs it with the CA’s private key.  => All users can then check the certificate with the CA’s public key. Public Key Infrastructure Certificate Authority (CA) Manages and signs Certificate Revocation Lists (CRLs) ‐> List of revoked certificates. Known CA’s are for instance the companies Verisign and DigiCert. A CA can also be installed and owned by a company to generate certificates for its employees, contractors, partners etc. (in‐house CA).  A CA may also be given the task of generating the asymmetric key pair. Public Key Infrastructure Registration Authority (RA)  Performs certain administrative functions on behalf of the CA.  Verifies user requests for a digital certificate and tells the CA to issue it.  Might be part of the CA or might be a different entity/organisation.  The CA retains sole responsibility for signing either digital certificates or CRLs. Public Key Infrastructure  Registration Authority (RA)  The functions of the RA could be :  Verifying the information provided by the subject (personal authentication functions).  Verification of the individual's right to the requested certificate attributes.  Verification that the individual actually possesses the private key corresponding to the public key requested for a certificate (commonly referred to as proof of possession [POP = Proof of Possession]).  Notification of compromised or expired keys that should be on CRL list.  Distributing the physical tokens (such as smart cards) that contain the private keys A real-life example - Certificate on identity card  In Belgium (like in many other countries), everybody has a digital certificate with their public key in the chip of their ID.  The RA is here the town hall which controls the identity of the user and which asks the government to create a digital certificate.  The CA is a Belgian government department CERTIPOST which creates and issues the digital certificate on request of the Town Hall (the RA).  The certificate is put on the chip on the ID card and delivered to the user by the Town Hall (the RA). The ID card contains:  Authentication Certificate: Used for logging into web applications, such as government portals.  Signature Certificate: Used for digitally signing documents (E.g. using Acrobat Reader). Quantum Computing and Cryptography  May solve some of the existing problems with current cryptographic systems  Generate perfectly random symmetric cryptographic keys  Secure distribution of symmetric cryptographic keys.  It is based on a practical application of the characteristics of the smallest “grains” of light (photons) and the physical laws governing their generation, propagation and detection.  It is impossible to eavesdrop and see for instance the key exchange as – simplified ‐ a quantum state (so the key) changes when observed (Heisenberg’s principle).  Could in the future “crack” some existing key lengths in no time.  Currently, we are preparing with quantum‐resistant key lengths and algorithms. Quantum Computing and Cryptography  Post‐Quantum Cryptography (PQC): NIST recently finalized the first set of post‐quantum cryptography standards, designed to withstand attacks from quantum computers  Quantum Key Distribution (QKD): This technology uses quantum mechanics to securely distribute encryption keys.  Immune to brute‐force attacks, even from quantum computers  Requires specialized hardware  Distance limitations. Quantum Computing and Cryptography  Quantum Random Number Generation (QRNG): Uses quantum properties to generate truly random numbers, which are crucial for cryptographic keys.  Current Quantum Computing Capabilities:  Large‐scale, fault‐tolerant quantum computers not yet commercially available.  Experts predict that quantum computers capable of breaking current encryption methods could emerge within the next decade (others say 30 years). Voettekst 51 Applications - Transport Layer Security (TLS)  TLS is a cryptographic protocol that provides secure communications on the Internet.  A session‐layer (OSI) protocol widely used for communication between browsers and web servers.  Provides:  Confidentiality of the communication  Endpoint authentication  Is destined to replace the older and less secure SSL (Secure Socket Layer) protocol. TLS and SSL are NOT interoperable. Applications - Secure Hypertext Transfer Protocol (HTTPS)  HTTPS is similar to HTTP, just with an encrypted session via TLS (or SSL) protocols.  HTTPS serves to secure World Wide Web pages for Applications.  In electronic commerce, authentication may be used:  in business‐to‐business (B‐to‐B) activities (for which both the client and the server are authenticated)  business‐to‐consumer (B‐to‐C) interaction (in which only the server is authenticated).  Using https:// instead of http:// directs the communication to a different port Applications - Virtual Private Network (VPN)  VPN is a collective name for all different VPN implementations. One popular VPN technology is IPSec.  Before VPN, the only way to have a “private” network was to own or lease your own lines. ‐> Expensive solution.  A VPN creates a secure private network over the public telecommunications infrastructure using encryption ‐> cheap solution.  Uses authentication and encryption between two Internet points ‐> confidentiality and integrity. Applications - Secure Shell (SSH)  Implemented at the Application layer in the TCP/IP model.  Provides a secure channel over an unsecured network by using a client‐server architecture, connecting an SSH client application with an SSH server.  Typically used to log in to a command shell on a remote machine and execute commands. (≈ as command prompt in Windows but commands are executed on a remote machine and not on yours)  Replaces Telnet and other unsecure remote shells.  Uses strong cryptography to protect data, including passwords (*), binary files and administrative commands. Uses digital certificates for mutual authentication. (*) Telnet sends passwords in readable form over the communication line.... Applications - Secure Multipurpose Internet Mail Extensions (S/MIME)  A standard secure email protocol  Security Properties:  Authenticates the identity of the sender and receiver  Verifies message integrity  Ensures the confidentiality of a message’s contents, including attachments  Non‐repudiation  Uses asymmetric encryption and uses digital signatures.  Can be used in e.g. Outlook Applications - Encryption of data at rest (Stored Data)  Encryption of data at rest as many benefits:  Encryption is better than only passwords or ACLs for protecting files.  Encryption moves with the data.  Encryption protects the confidentiality of the data from system administrators and hackers.  What can we encrypt?  Files: on‐the‐fly encryption/decryption  Disks: an unencrypted disk has all data visible (takes a hacker minutes)  Email encryption  Record (in a database) encryption. Cryptanalysis  The art of breaking cryptographic protection by  Finding weaknesses in existing algorithms, protocols and standards  Finding the secret or private key(s)  Finding the plaintext, based on a ciphertext Cryptanalysis  Some methods:  Known plaintext attack ‐> try to discover key  Chosen plaintext attack ‐> try to discover key (better than known plaintext)  Ciphertext only attack ‐> for old algoritms only ‐> check character frequencies etc.  Side‐channel attack: get some info on the algorithm by observing speed it takes on a CPU, electromagnetic radiation from the encrypting system, acoustics of typing from the user (which might divulge the key)… Cryptanalysis  Some more in‐depth methods:  Differential cryptanalysis attack: analyzes the difference after encryption between pairs of chosen plaintext.  Integral cryptanalysis attack: Keep part of the plaintext and vary the rest. Application of Hashing - Protection of passwords  Why not store passwords in cleartext? Though many still do…  Possible exception: safe storage like smart card, but still not very secure  Why not encrypt passwords? ‐> Hash is a faster solution without the verifier knowing the password:  But same password = same hash  => “salted”hashes Adds a random string to the password before hashing => (same password ≠ same hash). Usually, the salt is then added to the hash in front between two $ characters. Application of Hashing - Protection of passwords  Password attacks  Brute force ‐> rainbow tables  Lists of known passwords, dictionaries, knowledge of your victim  Have you been p’wned? Password Entropy A measure of how unpredictable (random) and secure a password is against guessing and brute‐force attacks. It quantifies the difficulty an attacker would have in finding the password. Calculation: 𝐸 𝐿 log 𝑅 bits  𝑬 is the entropy in bits.  𝑳 is the length of the password in number of places for characters.  𝑹 is the size of the character set used for each place in the password.(Example: 52 for both uppercase and lowercase letters in the Western alphabet)  If there are different rules for different pieces of the password, then calculate the entropy for each piece and add it up. Voettekst 63 Password Entropy  Importance of Entropy:  Low entropy: Easy to guess, vulnerable to attacks.  High entropy: Harder to guess, safer.  Entropy only indicates how strong a password can be at a given L and R.It is still possible to create weak passwords at a given L and R.  Example :  Passwords such as “IncoRRect77$%&”  𝑳 14  𝑹 94 (including lowercase, uppercase, numbers and special symbols).  The entropy is calculated as follows: 𝐸 14 log 94 14 6.5545 91.76 bits Voettekst 64 Password Entropy  Improve Entropy:  Greater length: Longer passwords have higher entropy.  Use different characters: Use uppercase, lowercase, numbers and special symbols to increase the character set.  Practical :  Non‐vital users: at least 50 bits of entropy.  Important users: 60‐80 bits of entropy.  Crucial users: 100 bits of entropy or more. Voettekst 65 Misuse of encryption Like dynamite, encryption can be misused by criminals:  Ransomware (Wannacry, Cryptolocker, Petya)  Hide malware code  Secret communications between criminals ‐> complicates forensic investigation  Encryption of data at rest by criminals ‐> complicates forensic investigation Encryption Risks Security mainly relies on the secrecy of the keys. The more a key is used, the more its data can be analyzed so the more vulnerable it is.  Password cracking tools get faster and faster with the evolution of technology  Sooner or later, a key will become obsolete Randomness of key generation is also a factor.  Sometimes key generation is based on passwords and it is easier to guess a password than a key ‐> key becomes less secure.  Randomness also plays a key role in asymmetric key generation.