Chapter 2 Crypto Basics Flashcards
what is cryptology
the art and science of making and breaking “secret codes”
what is cryptography
MAKING secret codes
what is cryptanalysis
BREAKING secret codes
what is the result of an encryption
cipher-text
what is used to configure a crypto-system
a key
what is a symmetric key
a cryptosystem that uses the same key to encrypt as to decrypt
what is a public key
a cryptosystem that uses a public key to encrypt and a private key to decrypt
what is kerckhoffs principle
the system is completely known to the attacker, only the key is secret, that is crypto algorithms are not secret
why do we make assumptions in kerckhoffs principle
experience has shown that secret algorithms are weak when exposed, secret algorithms never remain secret, better to find weaknesses before hand
The picture of crypto as a black box is aslo called
symmetric key crypto
in the symmetric key crypto what can trudy see
the encrypt, the decrypt, some of the plain text but not the key
for simple substitution the shift is called
caesars cipher
when trying all possibilities it is called
exhaustive key search
In general simple substitution key can be any ________ of letters
permutation, 26! > 2^88
what is secure cryptanalysis
cryptosystem is secure if best know attack is to try all keys
what is insecure cryptanalysis
cryptosystem is insecure if any shortcut attack is known
what is a one time pad encryption
Encryption: Plaintext XOR Key = Ciphertext
what is one time pad decryption
Decryption: Ciphertext XOR Key = Plaintext
what is one time pad
probably secure ciphertext provides no info about plaintext all plaintexts are equally likely pad is random pad only used once pad is only known to sender and receiver pad is the key pad is same size as message
what is the real world example of one time pad
VENONA
what is a codebook cipher
a book filled with codewords
what did code books also use
additives
what is a codebook additive
book of random numbers
what are the steps for additive in code book
encrypt message with code book choose position in additive book add additives to get cipher text send ciphertext and additive position recipient subtracts additives before decrypting
