Cryptography
The goals of Cryptography:
C.I.A. + Nonrepudiation
Nonrepudiation - Means by which a recipient can ensure the identity of the sender and neither party can deny sending.
Basic Terms & Concepts
Cryptography
Science or study of protecting information whether in transit or at rest
Renders the information unusable to anyone who can't decrypt it
Takes plain text, applies cryptographic method, turn it into cipher text
Cryptanalysis
Study and methods used to crack cipher text
Linear Cryptanalysis
Works best on block ciphers
Differential Cryptanalysis
Applies to symmetric key algorithms
Compares differences in the inputs to how each one affects the outcome
Integral cryptanalysis
input vs output comparison same as differential; however, runs multiple computations of the same block size input
Plain text doesn't necessarily mean ASCII format - it simply means unencrypted data
Key clustering - Different encryption keys generate the same ciphertext from the same plaintext message
Where to Encrypt & Decrypt?
Data-in-Transit / Data-in motion: Transport / Network
Not much protection as it travels
Many different switches, routers, devices
Network-based protection:
Firewall, IPS
Provide transport encryption:
TLS, IPsec
Data-at-Rest: Resides in storage
Hard drive, SSD, flash drive, etc
Encrypt the data
Whole disk encryption
Database encryption
File or/ folder-level encryption
Apply permissions
Access control lists
Only authorized users can access the data
Data-in-use / Data-in-process: RAM & CPU
The data is in memory or CPU registers and cache
The data is almost always decrypted
Encryption Algorithms
Algorithm - step-by-step method of solving a problem
Two General Forms of Cryptography
Substitution - bits are replaced by other bits
Transposition - doesn't replace; simply changes order
Encryption Algorithms - mathematical formulas used to encrypt and decrypt data
Steam Cipher - readable bits are encrypted one at a time in a continuous stream
Usually done by an XOR operation
Work at a high rate of speed
Block Cipher - data bits are split up into blocks and fed into the cipher
Each block of data (usually 64 bits) encrypted with key and algorithm
Are simpler and slower than stream ciphers
XOR - exclusive or; if inputs are the same (0,0 or 1,1), function returns 0; if inputs are not the same (0,1 or 1,0), function returns 1
Key chosen for cipher must have a length larger than the data; if not, it is vulnerable to frequency attacks
Symmetric Encryption
Symmetric Encryption - One Single Key / Session Key to encryption and decryption.
Known as:
Single key cryptography
Secret key cryptography
Shared key cryptography
Session key cryptography
One key is used to encrypt and decrypt the data.
Suitable for large amounts of data
128-bit or larger symmetric keys are common
Harder for groups of people because more keys are needed as group increases
Can be very fast to use
Less overhead than asymmetric encryption
Often combined with asymmetric encryption
Problems/Weaknesses of Symmetric Encryption:
Problems include key distribution and management / not scalable
Non-repudiation possible because everyone has a copy of the key
Key must be regenerated whenever anyone leaves the group of keyholders
Cryptosystem
Defines key properties, communication requirements for the key exchange; actions through encryption and decryption process.
e.g.: Using asymetric encryption to exchange Session keys after that communicate using Symmetric encryption.
Key escrow (also known as a “fair” cryptosystem) is an arrangement in which the keys needed to decrypt encrypted data are held in escrow so that, under certain circumstances, an authorized third party may gain access to those keys.
Symmetric Cryptosystems:
| Algorithm | Block or Streaming | Block Size | Rounds | Key Size | Notes |
|---|---|---|---|---|---|
DES | Block | 64-bit | 16 | 56 bits | Uses five modes of operation: ECB, CBC, CFB, OFB and CTR. |
Blowfish | Block | 64-bit | 16 | 32-448 bits | Public domain algorithm. |
Twofish | Block | 128-bit | 16 | 128, 192 and 256 bits | Public domain algorithm. |
3DES | Block | 64-bit | 16 | 168 bits (56 x 3) | Repeats DES process 3 times. |
AES | Block | 128-bit | 10, 12, or 14 | 128, 192 or 256 bits | Encryption standard for the US Gov.; Used in WPA2 |
RC4 | Streaming | N/A | 1 | 40-2048 bits | Used in WEP, SSL and TLS; largely deprecated in current;technologies. |
IDEA | Block | 64-bit | 8 | 128 bits | Made for replacement for the DES |
Larger keys than symmetric encryption; Common to see key lengths of 3,072 bits or larger
Asymmetric Encryption
Uses a Key pair:
Public Key - Anyone can see this key; give it away
Private Key - Keep this private; used for decryption; The private key is used to digitally sign a message.
Algorithms:
Diffie-Hellman - Developed as a key exchange protocol; used in SSL and IPSec; if digital signatures are waived, vulnerable to MITM attacks
Elliptic Curve Cryptosystem (ECC) - Uses points on elliptical curve along with logarithmic problems; uses less processing power; good for mobile devices
RSA - Achieves strong encryption through the use of two large prime numbers; factoring these create key sizes up to 4096 bits; modern de facto standard
El Gamal - Not based on prime number factoring; uses solving of discrete logarithm problems
Only downside is it's slower than symmetric especially on bulk encryption and processing power
Hashes
One-way encryption
Verify the Integrity of the message.
Verify the authenticity of the message (proof of origin & non-repudiation)
Impossible to recover the original message from the digest
Used to store passwords providing confidentiality.
| Hash | Algo. |
|---|---|
MD5 | 128 bit hash |
SHA-1 | 160 bit hash |
SHA256 | 256 bit hash |
Examples:
⚠️ If you change a single character, the entire Hash value changes. See the example below, changing the last character '!' to '.'
String: hello world!
MD5 Hash: FC3FF98E8C6A0D3087D515C0473F8677
String: hello world.
MD5 Hash: 3C4292AE95BE58E0C58E4E5511F09647
Message digest
A message digest or hash, can be used to verify the integrity of a message by comparing the original hash to one generated after receipt of the message. If the two match, then integrity is assured. If they do not match, then the message was altered between transmission and receipt.
⚠️ Message digests are also called:
hashes
hash values
hash total
CRC
fingerprint
checksum
digital ID
Hashing Algorithms
MD5 - Message Digest Algorithm
First published in April 1992
Replaced MD4
128-bit hash value
1996: Vulnerabilities found
Not collision resistant
⚠️ Collision - occurs when two or more files create the same output
Can happen and can be used an attack; rare, though
⚠️ Key space - Represents the total number of possible values of keys in a cryptographic algorithm or other security measure, such as password
⚠️ DUHK Attack (Don't Use Hard-Coded Keys) - allows attackers to access keys in certain VPN implementations; affects devices using ANSI X9.31 with a hard-coded seed key
⚠️ Rainbow Tables - contain precomputed hashes to try and find out passwords
SHA - Secure Hash Algorithm
Developed by NSA
SHA-1
Widely used
160-bit digest
Weak; 2005: Collision attacks published
SHA-2 Family
SHA-256 | minor version: SHA-224
SHA-512 | minor version: SHA-384
SHA-3
Uses a hash function called Keccack and has the same length of SHA-2.
SHA-1 and SHA-2 have been replaced by the latest iteration of SHA known as SHA-3.
HMAC
Hash Message Authentication Code - Used in conjunction with symmetric key both to authenticate and verify integrity of the message.
Verify data integrity and authenticity
No fancy asymmetric encryption is required
Used in network encryption protocols
IPsec, TLS
Requires each side of the conversation to have the same key
RIPEMD
RACE Integrity Primitives Evaluation Message Digest.
Not very common
Open Standard
128, 168, 256, 320 bit digests (RIPEMD-128, RIPEMD-256, RIPEMD-320)
Original RIPEMD was found to have collision issues (2004)
Effectively replaced with RIPEMD-160 (no known collision issues)
Based upon MD4 design but performs similar to SHA-1
Keystretching
Combine a very long salt and a huge number of hashing iterations to make cracking even more harder. (e.g Hashing the hashed password N times)
Two most popular Key stretching libraries/ functions:
PBKDF2 (Password-Based Key Derivation Function 2) algorithm
Part of RSA public key cryptography standards (PKCS #5, RFC 2898)
bcrypt
Generates hashes from passwords
An extension to the UNIX crypt library
Uses Blowfish cipher to perform multiple rounds of hashing
Example:
PBKDF2
bcrypt
⚠️ Key streaming - involves sending individual characters of the key through an algorithm and using a mathematical XOR function to change the output.
Cryptographic nonce
Cryptographic randomization schemes
Used once - 'for the nonce'/ for the time being
A random or pseudo-random number
Somehting that can't be reasonably guessed
Can also be a counter
Use a nonce during the login process
Server gives you a nonce
Calculate your password hash using the nonce
Each password hash sent to the host will be different, so a replay attack won't work
Initialization vectors (IV)
Is a type of nonce
Used for randomizing an encryption scheme
The more random the better
Use in encryption ciphers, WEP, and older SSL implementations
Digital Signatures
When signing a message, you sign it with your private key and the recipient decrypts the hash with your public key
Digital Signature Algorithm (DSA) - used in generation and verification of digital signatures per FIPS 186-2
⚠️ Digital Signature Standard (DSS):
Document that NIST puts out to specify the digital signature algorithms & the encryption algorithms approved for use by the US gov.
PKI System
Public Key Infrastructure (PKI) - structure designed to verify and authenticate the identity of individuals
Also refers to the binding of public keys to people or devices
The certificate authority (CA)
It's all about trust
X.509 v3 is current format most widely used. Part of the X.500 family of standards
Digital Certificates
Certificate - electronic file that is used to verify a user's identity; provides nonrepudiation
X.509 - standard used for digital certificates
Contents of a Digital Certificate:
Version - identifies certificate format
Serial Number - used to uniquely identify certificate
Subject - who or what is being identified
Algorithm ID (Signature Algorithm) - shows the algorithm that was used to create the certificate
Issuer - shows the entity that verifies authenticity
Valid From and Valid To - dates certificate is good for
Key Usage - what purpose the certificate serves
Subject's Public Key - copy of the subject's public key
Optional Fields - Issuer Unique Identifier, Subject Alternative Name, and Extensions
Some root CAs are automatically added to OSes that they already trust; normally are reputable companies
Self-Signed Certificates - certificates that are not signed by a CA; generally not used for public; used for development purposes
Signed by the same entity it certifies
Registration Authority
Verifies user identity
Certificate Authority
Third party to the organization; creates and issues digital certificates
Certificate Revocation List (CRL)
Used to track which certificates have problems and which have been revoked
Validation Authority
Used to validate certificates via Online Certificate Status Protocol (OCSP)
Trust Model
How entities within an enterprise deal with keys, signatures and certificates
Cross-Certification
Allows a CA to trust another CS in a completely different PKI; allows both CAs to validate certificates from either side
Single-authority system
CA at the top
Hierarchical trust system
CA at the top (root CA); makes use of one or more RAs (subordinate CAs) underneath it to issue and manage certificates
Key Wrapping and Key Encryption Keys (KEK)
KEKs are used as part of key distribution or key exchange.
key Wrapping - Protect session keys
If the cipher is a symmetric KEK, both the sender and the receiver will need a copy of the same key
If using an asymmetric cipher, with public/private key properties, to encapsulate a session key, both the sender and the receiver will need the other's public key
⚠️ Protocols such as SSL, PGP, and S/MIME use the services of KEKs to provide session key confidentiality, integrity, and sometimes to authenticate the binding of the session key originator and the session key itself.
Full Disk Encryption - FDE
Data at Rest (DAR) - data that is in a stored state and not currently accessible
Usually protected by full disk encryption (FDE) with pre-boot authentication
Example of FDE is Microsoft BitLocker and McAfee Endpoint Encryption
FDE also gives protection against boot-n-root
Encrypted Communication
Often-Used Encrypted Communication Methods:
Secure Shell (SSH) - secured version of telnet; uses port 22; relies on public key cryptography; SSH2 is successor and includes SFTP
Secure Sockets Layer (SSL) - encrypts data at transport layer and above; uses RSA encryption and digital certificates; has a six-step process; largely has been replaced by TLS
Transport Layer Security (TLS) - uses RSA 1024 and 2048 bits; successor to SSL; allows both client and server to authenticate to each other; TLS Record Protocol provides secured communication channel
Internet Protocol Security (IPSEC) - network layer tunneling protocol; used in tunnel and transport modes; ESP encrypts each packet
PGP - Pretty Good Privacy; used for signing, compress and encryption of emails, files and directories; known as hybrid cryptosystem - features conventional and public key cryptography
S/MIME - standard for public key encryption and signing of MIME data; only difference between this and PGP is PGP can encrypt files and drives unlike S/MIME
Heartbleed - attack on OpenSSL heartbeat which verifies data was received correctly
Vulnerability is that a single byte of data gets 64kb from the server
This data is random; could include usernames, passwords, private keys, cookies; very easy to pull off
nmap -d --script ssl-heartbleed --script-args vulns.showall -sV [host]Vulnerable versions include Open SSL 1.0.1 and 1.0.1f
CVE-2014-0160
FREAK (Factoring Attack on RSA-EXPORT Keys) - man-in-the-middle attack that forces a downgrade of RSA key to a weaker length
POODLE (Paddling Oracle On Downgraded Legacy Encryption) - downgrade attack that used the vulnerability that TLS downgrades to SSL if a connection cannot be made
SSl 3 uses RC4, which is easy to crack
CVE-2014-3566
Also called PoodleBleed
DROWN (Decrypting RSA with Obsolete and Weakened Encryption) - affects SSL and TLS services
Allows attackers to break the encryption and steal sensitive data
Uses flaws in SSL v2
Not only web servers; can be IMAP and POP servers as well
Cryptography Attacks
Cryptographic attacks approaches that seek to exploit one or more vulnerabilities in a cryptosystem to break it; Note: Patterns Kill! and it's all about the key!
Frequency Analysis & the Ciphertext Only Attack
Examine frequency of letters appearing in the ciphertext
Attempt to figure out what letters they correspond to plaintext
Known Plain-text attack
Has both plain text and cipher-text; plain-text scanned for repeatable sequences which is compared to cipher text
Chosen Cipher-text Attack
Chooses a particular cipher-text message
Attempts to discern the key through comparative analysis
RSA is particularly vulnerable to this
Chosen Plain-text attack
Attacker encrypts multiple plain-text copies in order to gain the key
Adaptive chosen plain-text attack
Attacker makes a series of interactive queries choosing subsequent plaintexts based on the information from the previous encryptions; idea is to glean more and more information about the full target cipher text and key
Cipher-text-only attack
Gains copies of several encrypted messages with the same algorithm; statistical analysis is then used to reveal eventually repeating code
Replay attack
Usually performed within context of MITM attack
Hacker repeats a portion of cryptographic exchange in hopes of fooling the system to setup a communications channel
Doesn't know the actual data - just has to get timing right
Side-Channel Attack
Monitors environmental factors such as power consumption, timing and delay
Meet-in-the-Middle
Used against algorithms that use 2 rounds of encryption. (reason that 2-DES was defeated).
Man-in-the-Middle
Birthday Attack / Collision Attack / Reverse Hash matching
Find flaws in the one-to-one association of the hash function
Timing Attack
Based on examining exact execution times of the components in the cryptosystems
Rubber-Hose Attack
Based on the use of threats or torture to extract need information
Don't Use Hard-Coded Keys (DUHK) Attack
Used against hardware/software that implements ANSI X9.31 Random Number Generation.
Social Engineering Attack
Social eng. can be very efficient to grab passwords etc
Tools
Carnivore and Magic Lantern - used by law enforcement for cracking codes
L0phtcrack - used mainly against Windows SAM files
John the Ripper - UNIX/Linux tool for the same purpose
PGPcrack - designed to go after PGP-encrypted systems
CrypTool
Cryptobench
Jipher
Keys should still change on a regular basis even though they may be "unhackable"
Per U.S. government, an algorithm using at least a 256-bit key cannot be cracked
How to defeat attack:
Salt the passwords - A nonce most commonly associated with password randomization, making the pasword hash unpredictable.
If the password database is breached, you can't correlate any passwords because even users with the same password have different hashes stored.
Pepper - A large constant number stored separately from the hashed password.
Key stretching - Combine a very long salt and a huge number of hashing iterations to make cracking even more harder. (e.g Hashing the hashed password N times).
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