Public key encryption each user has a pair of keys

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Public-Key Encryption Each user has a pair of keys: public key private key What is encrypted with one, can only be decrypted with the other
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Encryption Plain text Plain text Transmitted ciphertext Bob’s public key Alice Bob Bob’s private key
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Authentication Plain text Plain text Transmitted ciphertext Alice’s public key Alice Bob Alice’s private key
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Public-Key Encryption Algorithms RSA (used by PGP) El Gamal (used by GnuPG)
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Key Management Public-Key encryption can be used to distribute secret keys for conventional encryption Public-Key authentication: signing authority web of trust
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Digital Signature Like authentication, only performed on a message authenticator (SHA-1)
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Message Authentication Authentic message means that: it comes from the alleged source it has not been modified
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Message Authentication Approaches Authentication with conventional encryption Authentication without message encryption: when confidentiality is not necessary when encryption is unpractical
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Message Authentication Code Uses a secret key to generate a small block of data MAC M = F (K AB , M)
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One-way Hash Function Message digest – a “fingerprint” of the message Like MAC, but without the use of a secret key
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