EP47 - AskDeveloper Podcast - Cryptography - Part 2 - Encryption - a podcast by Mohamed Elsherif, Amr Eldib, Yasser Makram, Tamer Zaki & Ahmed Elmalt

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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 seconds128 bits 1.02 * 1018 years
192 bits 1.87 * 1037 years256 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 key5. 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 Key2. 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
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