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Methods of Encryption
Symmetric Cryptography:
Both parties will be using the same key for encryption and decryption. Can only provide confidentiality. They are fast and can be hard to break.
Strength - Much faster than asymmetric systems / Hard to break if using a large key size
Weaknesses - Key distribution (requires a secure mechanism to deliver key properly) / scalability (each pair of users needs a unique pair of keys) / Limited security (can only provide confidentiality)
Out-of-band method: The key is transmitted through another channel than the message.
Asymmetric Algorithms:
Two different asymmetric keys are mathematically related, public and private key.
Strengths - Better key distribution than symmetric systems / better scalability than symmetric systems / can encrypt confidentiality, authentication and nonrepudiation
Secure message format - Encrypted by the receiver's public key
Open message format - Encrypted by the sender's private key
Secure and signed format - Encrypted by the senders private key and then encrypted with the receivers public key
Two types of symmetric algorithms
Stream ciphers:
Treats the message as a stream of bits or bytes and performs mathematical functions on them individually. The key is a random value input into the stream cipher, which it uses to ensure the randomness of the keystream data. Are more suitable for hardware implementations, because they encrypt and decrypt one bit at a time. Are intensive because each bit must be manipulated, which works better at the silicon level.
Characteristics of a strong and effective cipher algorithm - Long periods of no repeating patterns within keystream values / statistically un predictable / the keystream is not linearly related to the key / statistically unbiased keystream (as many 0's as 1's)
Key stream generator - Produces a stream of bits that is XORed with the plaintext bits to produce cipertext.
Block ciphers:
The message is divided into blocks of bits. Uses diffusion and confusion in their methods. Uses Substitution boxes (S-boxes) In each step. It is the key that determines what functions are applied to the plaintext and in what order. Are more suitable for software implementations, because they work with blocks of data which is usually the width of a data bus (64 bits). Block ciphers sometimes work in a mode that emulates a stream cipher.
Confusion - Different unknown key values are used.
Diffusion - Putting the bits within the plaintext through many different functions so that they are dispersed throughout the algorithm.
S-box - Contains a lookup table that instructs how the bits should be permuted or moved around. The key that is used in the decryption process dictates what S-boxes are used and in what order.
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