2019/11/22
HIT Mooc-- computer network: Job 9
If the single code substitutes alternate password (key) as follows:
明文:abcdefghijklmnopqrstuvwxyz
Ciphertext: mnbvcxzasdfghjklpoiuytrewq
1) Please encrypt the message "This is an easy problem";
2) to decrypt the message "rmij'u uamu xyj".
my answer
No
standard answer
No
2 (6 points)
Suppose the attacker can encrypt a plain text "The quick brown fox jumps over the lazy dogs", and the ciphertext. I ask you:
1) whether the attacker can take advantage of chosen plaintext attack all the packets to crack a single code alternate password? why?
2) whether the attacker can take advantage of chosen-plaintext attack to crack multi-code all messages alternate password? why?
my answer
No
standard answer
No
3 (8 minutes)
Consider p RSA algorithm = 5 and q = 11 in. I ask you:
1) What n and z are?
2) If so e = 3, e Why is a reasonable choice?
3) Find d is a de mod z = 1, and de <160;
4) using a key (n, e) the encrypted message m = 8. (Tip: [(a mod n) * (b mod n)] mod n = (a * b) mod n)
my answer
No
standard answer
No
4 (10 minutes)
Assumed to be shared between Alice and Bob two keys: a message authentication key S1 and a symmetric encryption keys S2. Please use a communication scheme illustrated design, required to support message integrity and confidentiality.
my answer
No
standard answer
No
5 (10 minutes)
Suppose Alice wants to send a message to Bob; Bob has a public - private key pair (KB +, KB -), Alice has Bob's certificate, but Alice is not public - private key pairs; Alice and Bob share the same hashing function H (·). please answer the following question:
1). In this case, if you can design a program so that Bob can verify the e-mail messages by Alice created? If so, please explain draw a block diagram of the program; simple if not, explain why.
2). Can design a program to support Alice send confidential messages to Bob? If you can, please draw the plan diagram; if not, please explain why.
my answer
No
standard answer
No
6 (6 points)
Suppose Alice and Bob SSL session-based communications. Suppose an attacker has no shared keys, insert a bogus TCP checksum TCP segment with the correct sequence number (with the correct IP address and port number) of the packet flows has. The receiving end receives the SSL TCP segment forged and submitted the upper application load it? why?
my answer
No
standard answer
No
Consider the following pseudo WEP protocol, a 4-bit shared key, set 1010; IV 2 bits, in generating a key stream, appended to the key. 4 kinds of key generation flow is as follows:
101000: 0010101101010101001011010100100 . . .
101001: 1010011011001010110100100101101 . . .
101010: 0001101000111100010100101001111 . . .
101011: 1111101010000000101010100010111 . . .
Assuming all message length is 8 bits; the ICV to 4 bits by 4 XOR resultant first 4 bits after the data; dummy WEP packet contains three fields: IV Field + message field + the ICV field, wherein the message field + the ICV fields are encrypted.
1). If it is desired to send a message m using the WEP protocol IV = 11 = 10100000, then the values of the three fields are WEP packet number?
2) Description When the receiving end decrypts the WEP packets, messages and how to restore the ICV.
3) Assuming a WEP Trudy intercepted packet (not necessarily IV = 11), and modifies the packet to the receiving end before forwarding, and Trudy does not know the key stream corresponding to any of IV. If Trudy flipped the first bit of ICV, which is Trudy / other bits must also be reversed, so that the packet can be modified by the ICV checking?
my answer
No
standard answer
No