By the end of today, you should:
Kinds of Encryption:
The weakness of private key encryption is the key distribution problem:
How do you securely transmit the secret key to your interlocutor so that you can securely communicate with them?
How can yousigna document without allowing others to forge your signature or to copy/paste your signature onto another document? Solved!
We'll cover digital signatures next time.
The trick is to come up with algorithms and key pairs where knowing P doesn't help Eve find S.
One such trick is factoring, which is the basis of the RSA (Rivest-Shamir-Adelman method). If P is the product of two very large prime numbers, and S is related to those prime factors, Eve can only find S by factoring P.
information that cannot be read without special information
the process of converting plaintext into ciphertext
the process of converting ciphertext into plaintext
the process of cracking the code with the use of a computer program
Which of the following codes is not a kind of cryptographic code?
The Caesar Code
The Vigenere Code
The ASCII Code
The Enigma Code
Assuming a Caesar code with rotation 10 and the use of the whole ASCII character set of 128 characters for typing a message, which of the following numbers will represent the letter lowercase z (its ASCII code is 122) in the ciphertext?
Do you see any problem with the setup described in Quiz Question Nr. 3?
Which of the following statements about breaking the Caesar Code is TRUE?
It is secure against all but brute-force attacks.
It can be broken only with the help of a computer to execute many trial-and-error runs.
It can be broken with the help of ASCII encoding and the modulo operator.
It can be broken with the help of statistical analysis.
The Vigenere Cipher is more secure if:
the codeword is short
the codeword is long
a different codeword is used for every message
the codeword has a known length
Systems that use private keys are
difficult to break, depending on the algorithm
difficult to break, depending on the private key
difficult to break, depending on the algorithm and private key
Which of the following statements is TRUE?
Public key encryption is insecure because it needs two keys.
Public key encryption is secure because it needs two keys.
Public key encryption is insecure because everyone knows your public key.
Public key encryption is secure because no one else knows your private key.
For simplicity, I may just demo this on a single machine, but you can test that I'm not cheating by doing the exercise.
(FYI, 2048 bits is considered barely acceptable for commercial websites, but takes 90+ seconds to compute on my office desktop computer, whereas 1024 bits takes just 5 seconds.)
Public Modulo (p*q)is. This is the value of n. Imagine trying to factor that to get p and q!
ciphertext in hex. (Notice how you now understand what
hexmeans: since the encryption is going to be a long string of bits, hex is incredibly useful here..)
Let's make this a bit more realistic. Choose a partner (say from the row in front of or behind you, so you can't easily look onto her monitor, though it doesn't really matter). One of you will be the sender and the other the receiver.
OpenPGP Multi Precision Integer (MPI) of Public Key (base64). (This is an encoding of both e and n, in one relatively compact representation.)
Notice the contrast between using public key and private key encryption. In private key encryption, as with Caesar and Vigenère, both the sender and receiver have the key and do pretty much the same thing. Thus, codes like that are called symmetric cryptosystems. In public key encryption, on the other hand, the sender and receiver do very different things. The receiver has to generate the public key that allows her to receive messages that only she can read; the sender doesn't know anything that Eve doesn't know. Thus, public key systems are also called asymmetric cryptosystems.
Public key encryption is useful because:
it is used by people who want to keep their communication secret from the government
it is used by websites such as Google, Facebook, Tumblr, etc.
it is used for financial transactions on the web
all of the above
But, of course, the most important thing it does is solve the key distribution problem.
Which of the following is TRUE:
the public key encrypts a message that is decrypted by the private key
the private key encrypts a message that is decrypted by the public key
both A and B
neither A nor B
We hope that after these activities you can:
Will be posted later, visit again after .
1. B 2. C ASCII just represents text using numbers 3. B because 122+10 = 132, but 132-128 is 4. The problem is that 4 is not a printable character, so we should boost them up to printable characters 4. D 5. B or C 6. D 7. D 8. D, of course 9. C