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16 Cards in this Set
- Front
- Back
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. Secrecy Protocols (conventional, public key)
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Alice encrypts a message, M with K(A,B)
•Alice transmits MK(AB) •Only Bob is able to read M because only Bob (and Alice) have K(A,B) |
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Integrity Protocols (conventional, public key)
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1. Automated detection means that the receiving system must perform a comparison operation between 2 items
2.Preventing intentional modifications means that at least one of the received items must be protected by some type of cryptography |
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Authenticity Protocols (conventional, public key)
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The value H(M)Alice-priis generally called Alice’s digital signature of M
•When a digital signature verifies it guarantees the authenticity and integrity of the messageMH(M)Alice-pri |
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Non-Repudiation Protocols
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Require a digital signature. Give a judge the message, public key, and digital signature.
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Hybrid encryption scheme
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Using Public Cryptography to Distribute Conventional Keys
The hybrid encryption scheme is commonly used in: –encrypted SMIME e-mail –PGP encrypted e-mail –secure web protocols like SSL |
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Digital Signature
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A hash value that has been encrypted with the sender’s private key.
The act of signing means encrypting the message’s hash value with a private key. |
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Encrypted
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Provides confidentiality
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Hashed
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Provides integrity
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Digitally Signed
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: Authentification, nonrepudiation, and integrity
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Encrypted and Digitally Signed
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Confidentiality, Authentification, nonrepudiation, and integrity
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Protocols
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A sequence of steps taken by two or more parties to accomplish some task
–Established in advance –Mutually subscribed –Complete and unambiguous: a specific action for every possible situation |
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Using Public Cryptography to Distribute a Conventional Key
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The essence is:
–Distribute the easy key (a Public Key) –Encrypt the short data (the Conventional Key) with the slow crypto (Public Key Crypto) –Encrypt the long data (the message) with the fast crypto (Conventional Crypto) |
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The Hybrid Scheme
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The sender steps are:
–Randomly create a Conventional Key –Encrypt it with the Public Key of the recipient –Send the encrypted Conventional Key to the recipient –Encrypt the message with the Conventional Key –Send the encrypted message to the recipient |
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Advantages of the Hybrid Scheme
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It uses the speed of Conventional encryption
•It uses the ease of Public Key distribution •The session key is only used once so there is no chance for an attacker to gather a lot of ciphertext encrypted with the same Conventional key |
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How many seconds does it take to encrypt a million (106) bit message using just the Public Key cipher?
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1 million / 1000 = 1000 seconds or 20 minutes
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How many seconds does the hybrid scheme take to encrypt the 1,000-bit Conventional session key? ________
•How many seconds does the hybrid scheme take to encrypt the 106-bit message? _______ •How many total seconds do both encryption steps take? ________ |
2 seconds
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