Bob bobs private key 15 key distribu7on this is a

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Unformatted text preview: a key in two parts: a public part (widely known), and a private part (only owner knows) –  Encryp7on is based on mathema7cs (e.g., RSA is based on difficulty of factoring) Computer Networks 12 6 12/3/13 Symmetric (Secret Key) Encryp7on •  Alice and Bob have the same secret key, KAB –  Anyone with the secret key can encrypt/decrypt Plaintext I♥networks Alice Plaintext I♥networks Encrypt Hi there Decrypt Ciphertext Secret key KAB KAB Bob Secret key Computer Networks 13 Public Key (Asymmetric) Encryp7on •  Alice and Bob each have public/private key pair (KB / KB- 1) –  Public keys are well- known, private keys are secret to owner Plaintext I♥networks Alice Plaintext I♥networks Encrypt Bob’s public key Computer Networks Hi there Decrypt Ciphertext KB KB- 1 Bob Bob’s private key 14 7 12/3/13 Public Key Encryp7on (2) •  Alice encrypts with Bob’s public key KB; anyone can send •  Bob decrypts with his private key KB- 1; only he can do so Plaintext I♥networks Alice Plaintext I♥networks Encrypt Hi there Decrypt Ciphertext Bob’s public key KB Computer Networks KB- 1 Bob Bob’s private key 15 Key Distribu7on •  This is a big problem on a network! –  OCen want to talk to new par7es •  Symmetric encryp7on problema7c –  Have to first set up shared secret •  Public key idea has own difficul7es –  Need trusted directory service –  We’ll look at cer7ficates later Computer Networks 16 8 12/3/13 Symmetric vs. Public Key •  Have complementary proper7es –  Want the best...
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