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Week 1

We want these:

• Confidentiality
• Integrity
• Authentication
• Non-repudiation

See the security properties notes from Forensics last semester

Cryptology can be broken into:

• Cryptanalysis - Breaking cryptosystems
  • Classical Cryptanalysis
    • Mathematical Analysis
    • Brute-force attacks
  • Implementation Attacks
  • Social Engineering
• Cryptography
  • Symmetric Ciphers
  • Asymmetric Ciphers
  • Protocols

Encryption of Plaintext yields Ciphertext:

\[e_K(x) = y\]

Decryption of Ciphertext yeilds Plaintext:

\[d_K(y) = x\]

The set of all keys is the Key Space:

\[\text{keyspace} = \{ K_1, K_2,\dots ,K_n \}\]

If the same key is used, encryption and decryption are inverse operations:

\[d_K(e_K(x)) = y\]

Kerckhoff’s Principle:

A cryptosystem should be secure even if the attacker knows all the details about the system, with the exception of the secret key

Meaning: Do not roll-your-own cryptosystem

Shift Cipher

Where \(k, x, y \in \{ 0, 1, 2, \dots , 25 \}\)

\[\begin {align} y = e_K(x) = x + k \bmod 26 \\ x = d_K(y) = y -k \bmod 26 \end {align}\]