Cryptography (1)

PlainText

Ciphertext

PlainText

Encryption

Decryption

• Most ciphers consists of public algorithm and a key which needs to be long to be safe (40, 56, 128 bits)

• Encryption and decryption is computationally expensive

• Brute force attack:
  • if it takes one day for a device to break 40 bit DES,
  • it takes 7 years for the same device to break 56 bit DES
  • it takes several billion years to break 112 bit 3DES

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