EP47 - AskDeveloper Podcast - Cryptography - Part 2 - Encryption

AskDeveloper Podcast

?????? ??????? 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. Our facebook Page http://facebook.com/askdeveloper On Sound Cloud http://soundcloud.com/askdeveloper Please Like & Subscribe