Cryptography

RSA, Rainbow Table attack Links: Khan Academy videos

13 flashcards · Computer Science · by lakesare

1. Hashing vs encrypting?

   Hashing is irreversible.

2. How to use Rainbow Table attack?

   Provided: we have a database with hashed passwords we have a list of possible passwords We can: hash_function(predefined_password) === hashed_password

3. How to prevent Rainbow Table attack?

   By using salts. 2 same passwords hashed with salts will result in different strings.

4. What is prime factorization?

   Decomposition of a composite number into a product of primes.

5. What does RSA stand for?

   Rivest–Shamir–Adleman.

6. What mathematical discovery would render RSA-based public-key cryptography insecure?

   An algorithm that efficiently factors an arbitrary integer.

7. What's the number that takes the longest to factor (using existing algorithms)?

   When this number = product of 2 primes of similar size. Among the b-bit numbers, the most difficult to factor in practice using existing algorithms are those that are products of two primes of similar size.

8. Write the xor operation in terms of mod

   The XOR operation isn't anything new—it's just the normal vector addition operation for vectors with coefficients in the finite field F2.

9. Explain why

   If there's 1 xor 1 - we toggle, resulting in 0. If there's 0 xor 0 - we leave the number as it is, resulting in 0. An important property of the XOR operation is that it is its own inverse.

10. Prove that:

    Use self-inverse property of XOR, and associative law for vector addition

11. Explain one-time pad cryptosystem. In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent.

    message ⊕ secret key = ciphertext ciphertext ⊕ secret key = message! Only Alice and Bob know secret key k. Secret key k is truly random. Alice and Bob must never reuse the secret key.

12. What's Indistinguishability under chosen-plaintext attack (IND-CPA)? If cryptosystem complies to IND-CPA, it means it's considered secure in terms of indistinguishability.This is one of the strongest security standards we can expect from a cryptosystem.

    When eavesdropper can't distinguish the ciphertexts of two messages ma and mb chosen by the eavesdropper, with a probability greater than guessing randomly. Eavesdropper does know the messages ma and mb! Криптосистема считается безопасной с точки зрения неразличимости, если ни один злоумышленник, получив шифротекст, случайно выбранный из двухэлементного пространства сообщений, определенного противником, не может идентифицировать соответствующий этому шифротексту открытый текст с вероятностью зн…

13. What's the text transformed from plaintext using an encryption algorithm called?

    Ciphertext.