Ask Developer - Cryptography

Information Security
 1. Introduction
  ○ Security by obscurity
   § Steganography
    □ Hiding data inside another form of data, like using non-used bits in image to hide a message
     § Cool, but not practical.
     § Disadvantages
      ◊ Algorithm secrecy vs. key secrecy
  ○ Cryptography is everywhere and yet if done right, you can barely see it.
  ○ Goals: 
   § Confidentiality
    □ Secrets stay secret.
   § Integrity
    □ Data is not tampered with.
   § Non-Repudiation
    □ No party can deny sending messages.
   § Authentication
    □ Each party can ensure that the sender is what they expect.
  ○ Cryptography
   § Hashing
   § Encryption
   § Signing
   § Protocols
  ○ Random Number Generators
   § Extremely important, almost all encryption/hashing strength is affected by how random the random number generator is.
   § Don't use simple random number, use a cryptographic random number generator with a sophisticated source of entropy.
   § Pseudorandom number generator
   § Dual_EC_DRBG random generator backdoor
 2. Body
  ○ Hashing (one Way)
   § Properties
    □ Fixed length output no matter what size the input was
    □ Very easy to compute the hash of a given message, however very hard to compute from a hash the corresponding input.
    □ Mathematically infeasible to generate a message that has a given hash
    □ Any modification to a message produces a completely different hash that has no relationship to the original message's hash.
    □ It is mathematically infeasible to find two messages with the same hash. Hash Collision
   § Hashing Functions
    □ Provides data integrity, however lacks authentication
    □ Examples
     ® MD5 
      ◊ Considered Insecure
     ® Secure Hash Family SHA-X, Sha-1, Sha-2 [Sha256, Sha512], Sha-3
      ◊ Sha-1 is considered insecure.
      ◊ Sha-1, Sha-2 designed by NSA
      ◊ Sha-3 is not designed by NSA, Competition winner.
    □ Attacks
     ® Brute force
      ◊ CPU's are getting faster and cheaper every day.
      ◊ GPU's are getting faster and cheaper every day.
      ◊ Special Hash calculating hardware is becoming more available especially with the BitCoin push.
     ® Rainbow table attacks
      ◊ Pre-Calculated tables where you can reverse lookup a hash to a value
      ◊ Try www.crackstation.net
   § Hash Message Authentication Codes (HMAC)
    □ Adds authentication to integrity
    □ Can be used with all previous algorithms, HMACMD5, HMACShA1, HMAC256 … etc.
   § Salted Hash
    □ Adds random salt to mitigate rainbow table
    □ Salts are unique per record, and not a secret.
   § Password Based Key Derivation Function (PBKDF2)
    □ RSA Public Key Cryptographic Standard PKCS #5 Version 2.0
    □ Internet Engineering Task Force RFC 2898 Specification
     ® Adds a lot of iterations to slow it just enough to mitigate brute force (default 50,000 iterations)
     ® Adds random salt to mitigate rainbow table
    □ Disadvantage: It can be easily implemented with hardware which makes it vulnerable to bruteforce even with high number of iterations
   § Bcrypt
    □ Password Hashing function
    □ State of the art password hashing
   § Usages
    □ Integrity Check
Password Storage

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EP46 - AskDeveloper Podcast - Cryptography - Part 1 - Introduction and Hashing

الحلقة السابقة 
https://soundcloud.com/askdeveloper/ep46-askdeveloper-podcast-cryptography-part-1-introduction-and-hashing
○ Encryption (Two Ways)
   § Symmetric Encryption
    □ Same key both encrypts and decrypts the data.
    □ Very fast, yet exchanging key is tricky
    □ Very Algorithmic
    □ Examples
     ® DES Data Encryption Standard (BROKEN)
      ◊ Uses key of 56 bit length
     ® Triple DES (3DES)
      ◊ Uses three keys (or two unique keys) of 56 bit each
     ® AES Advanced Encryption Standard
      ◊ Uses keys of 128, 192 or 256 bits long
    □ Attacks
     ® Brute force
      ◊ Usually mitigated via increasing key length, as difficulty increases exponentially as key size increases, for example time to crack given a modern super computer.
      Key Size Time To Crack
      56 bits 399 seconds
      128 bits 1.02 * 1018 years
      192 bits 1.87 * 1037 years
      256 bits 3.31 * 1056 years
      ◊ Side-Channel Attacks
   § Asymmetric Encryption
    □ Key pairs have mathematical relationship
    □ Each one can decrypt messages encrypted by the other.
    □ Slow, but exchanging key is trivial
    □ Very Mathematical
    □ Anyone can know the Public Key
     ® The Public key can only be used to encrypt data
    □ The Private key is kept secret, and never leaves the recipient's side.
     ® The Private key can only be used to decrypt data
    □ Examples
     ® RSA (Rivest, Shamir and Adelman)
     ® The de-facto standard in the industry
     ® Public and Private keys are based on large Prime Numbers
   § Hybrid Encryption
    □ Uses both Symmetric and Asymmetric encryption at the same time.
    □ Goals:
     ® Use the performance of Symmetric Crypto 
     ® Convenience of sharing keys using Asymmetric Crypto
     ® HMAC for authentication.
    □ Steps: (Order is very important)
     ® Party 1 (Alice)
      1. Generates a random AES Session Key (32 bytes / 256 bits)
      2. Generates a random Initialization Vector (IV) (16 bytes / 128 bits)
      3. Encrypt the message to be sent using the AES Session Key & IV
      4. Calculate an HMAC of the encrypted message using the AES Session key
      5. Encrypt the AES Session Key using the Public Key of Party 2 (Bob) The recipient.
      6. Sends a packet of (Encrypted Message, Encrypted Session Key, Initialization Vector, and HMAC) to Bob
     ® Party 2 (Bob)
      1. Decrypts Session key using his Private Key
      2. Recalculates the HMAC of the encrypted message (Validates message integrity)
       } If HMAC check pass
        – Decrypts the message using the decrypted AES Session Key and Initialization Vector
       } Otherwise, rejects the message because of integrity check failure.


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EP47 - AskDeveloper Podcast - Cryptography - Part 2 - Encryption

○ Digital Signatures
   § Goal: verify Authenticity of a message.
   § Based on Asymmetric Cryptography.
   § Basic operations
    1. Public / Private keys generation (using some algorithm like RSA)
    2. Signing algorithm using the private key
    3. Signature verification algorithm using the corresponding public key
   i. Extending previous Example
    • Steps (Order is very important, bold stuff is the difference added to authenticate sender)
     ® Party 1 (Alice)
      1. Generates a random AES Session Key (32 bytes / 256 bits)
      2. Generates a random Initialization Vector (IV) (16 bytes / 128 bits)
      3. Encrypt the message to be sent using the AES Session Key & IV
      4. Calculate an HMAC of the encrypted message using the AES Session key
      5. Encrypt the AES Session Key using the Public Key of Party 2 (Bob) The recipient.
      6. Calculate Signature using the private signing key on the HMAC
      7. Sends a packet of (Encrypted Message, Encrypted Session Key, Initialization Vector, HMAC, and Signature) to Bob
     ® Party 2 (Bob)
      1. Decrypts Session key using his Private Key
      2. Recalculates the HMAC of the encrypted message (Validates message integrity)
       } If HMAC check pass
        – Verify digital signature using Alice Public Key
         w If signature verification pass
          w Decrypts the message using the decrypted AES Session Key and Initialization Vector
         w Otherwise, identity of the sender couldn't not be verified, reject message.
       } Otherwise, rejects the message because of integrity check failure.
    • Why Order matters?
     ® Timing Side-Channel Attacks
     ® Padding-Oracle Attack
     
  ○ Protocols
   § TLS/SSL
    • How TLS/SSL Works?
    • Mitigates against
     ® Man in the Middle Attacks
     ® Authentication, so the client can be sure it is talking to the correct destination.
   § Public Key Infrastructure (PKI)
    • Certificates aka X.509 Certificate (Sha-1 Signature Issues)
     ® A digitally signed file
     ® Identifies (Computer / User / Device)
     ® Has Public & Private Key, only the certificate owner has the Private Key.
     ® Has Expiration date
     ® Information about the CA that issued the cert 
     ® X.509 Extension Attributes (like Usage attribute)
     ® Revocation Information.
    • Certificate Authority (CA) (CNNIC, WoSign)
     ® Issues, signs and manages certificates.
     ® Famous certificate authorities (Verisign, GoDaddy, … etc).
    • Trust Chains
     ® CA's can delegate the signing job to subordinate CA's
      ◊ Root CA's signs an intermediate signing certificate to the subordinate CA
     ® The subordinate CA can then issue certificates
     ® To validate a certificate, the client validates the signatures of all the intermediate stages and make sure all of them are linked to a Trusted CA
    • Certificate Revocation Lists (CRL's)
     ® When a certificate is compromised (Private Key leaked) it will be published on the CRL, so each time the cert is validated, the CRL list is checked in case cert is revoked.
 3. Takeaways
 4. Books
  a. Understanding Cryptography: A Textbook for Students and Practitionershttps://www.amazon.com/Understanding-Cryptography-Textbook-Students-Practitioners/dp/3642041000


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