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Unformatted text preview: Lecture 6: Encryption with RSA Daniel Frances c 2012 Contents 1 Encryption 2 1.1 RSA algorithm theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1 How does Alice set her public key? . . . . . . . . . . . . . . . . . . . 3 1.1.2 How does Bob encrypt the AES key using Alices public key? . . . . . 3 1.1.3 How does Alice generate her private key? . . . . . . . . . . . . . . . . 3 1.1.4 How does Alice use her private key to decode the message y? . . . . . 4 1.1.5 How do we know this always works? . . . . . . . . . . . . . . . . . . 4 1.1.6 What prevents Eve  the intruder  from decoding y? . . . . . . . . . 6 1 Figure 1: RSA Encryption 1 Encryption Encryption over the Internet uses two algorithms: AES (Advanced Encryption Standard) and RSA (Ron Rivest, Adi Shamir and Leonard Adleman). AES encryption assumes that both the sender and receiver share a private key. A key is a number, represented by a bit length of either 64, 128, 256 bits. The longer the key the more secure the encryption. Only with the knowledge of this key can the message be encrypted and decrypted. These notes do not deal with the details of the AES algorithm. RSA encryption is used to securely provide a secure shared AES key to the receiver and sender of the message so that they can use the AES algorithm. It uses the concept of a private and public key. When you do banking transactions, both your computer and the bank have posted their public keys which are accessible to all. You each also have private keys which are not accessible. The encryption community uses the names Bob and Alice to refer to the sender and receiver of a message. In the case of AES, the message is the information that needs to be encrypted....
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 Spring '12
 Frances

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