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

Weekly Podcast discussing the Egyptian IT industry, and various other technology related topics 
راديو عربي على الانترنت من المبرمجين المصريين للمبرمجين, باللغة العربية و باللهجة المصرية