Security

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Security

• Meredith Friedman
• CS 111.01

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Aspects of Security
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Privacy

• The concept of confidentiality Only sender and
  receiver should have access to contents of a
  transmission.

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Authentication

• Assures the recipient knows who the sender is,
  and where the information is coming from.

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Integrity

• The idea that a transmission is received in
  exactly the same way it was sent.

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Nonrepudiation

• A guarantee that the sender is aware of what they
  are doing, and takes full responsibility. A
  secure server is able to prove who sent a
  message.

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Encryption

• Privacy requires that a message be encrypted at
  the sender site and decrypted at the receiver
  site so that a potential intruder cannot
  understand its contents.

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Types of Encryption

• Secret Key Encryption
• Public Key Encryption
• Combination (Secret and Public Key)

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Secret Key Encryption

• When the sender uses a secret key, an encryption
  algorithm encrypts the data.
• The receiver uses the same key with a decryption
  algorithm to decrypt the data.
• Data, when not encrypted, are called plaintext,
  encrypted data are called ciphertext
• Secret Key Encryption algorithms are also called
  Symmetric Encryption Algorithms because the same
  secret key is used in both directions of
  communication.

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Pros and Cons

• More efficient than Public Key Encryption
• Each pair of users must have a secret key so if
  1 million people want to communicate, they need
  to have a half-trillion secret keys.
• Distribution of keys between parties can be
  difficult

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Public Key Encryption

• This method uses 2 keys a private key kept by
  the receiver, and a public key that is announced
  to the public (i.e. via the internet).
• The most common public-key algorithm is named
  after its inventors Rivest-Shamir-Adleman (RSA)
  Ecryption.

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Pros and Cons

• Less keys needed- using Public Key Encryption, it
  would only take 2 million keys for 1 million
  people to communicate.
• The algorithm for a public key usually has very
  large numbers, so converting plain text from
  cipher text can take a long time.
• For this reason Public Key Encryption is not
  usually used for large amounts of text.

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Combining the Two

• You can combine the advantages of Secret Key
  (effciency) and Public Key (easy distribution of
  keys) algorithms.
• The public key is used to encrypt the secret key,
  while the secret key is used to encrypt the
  message.

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Any Questions?