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資訊安全導論期末作業
1. Explain the following basic requirements of information security
(a). The attacker cannot crack/decrypt/decipher the encrypt message
(b). The receiver hopes that the message was sent by sender, not forged by the other.
(c). The receiver can ensure that the message has not been tampered.
(d). The sender can not repudiate the message
2. S-boxes are important components in block ciphers such as DES or AES. In the 4x4 S-box given below(Table 1), 4 input bits are named x1, x2, x3 and x4 from left to right, and output y1, y2, y3, y4, respectively.
(a). Known-plaintext
(b). Chosen-plaintext
(c). 8/16
(d). 0
3. Consider an RSA cryptosystem whose public key is (n, e) = (5963, 3485)
(a). 67 * 89 = 5963, then p = 67, q = 89
(b). phi(n) = (67 - 1) * (89 - 1) = 66 * 88 = 5808, d = e^-1 mod phi(n) = 3485^-1 mod 5808 = 5
4. Answer the following question about RSA cryptosystems.
(a). Use same n to generate e1, e2, and same original message m was encrypted by e1, e2 respectively to c1, c2, then just find integer s, t satisfy e1s + e2t = 1, m = c1s*c2t(mod n)
(b). There are many public key with different n and same e, then it can use Chinese Reminder Theorem to calculate m
(c). encrypt the message repeatly until the original ciphertext c appears again, then the second to last ciphertext will be the plaintext message m.
(d). smaller gcd(p-1, q-1) can avoid Cycling attack.
The message is encrypted using symmetric encryption. Typically, a newly generated random message key (secret key) is used for the encryption. Symmetric encryption means that the same key is used for both encryption and decryption (a secret key). Anyone wanting to decrypt the message needs access to this key.
To transfer the secret key between the parties, the secret key is encrypted using the recipient’s public key.
The encrypted document and the encrypted message key are packed together in a single data packet to save or send to the intended recipient.
The recipient applies his or her private key to the encrypted message key. The result is the secret key that was originally used to encrypt the digital document.
The secret key that was revealed in the previous step is used to decrypt the digital document.
6. In a Diffie-Hellman key agreement between two persons A and B, (g, p) = (7, 67). A randomly chooses a = 3, and B randomly selects b = 6.
(a). A = ga = 73 (mod 67) = 8
(b). B = gb = 76 (mod 67) = 64
(c). K = gab = 73*6 = 40 (mod 67)
7. For certificates of public keys, answer the questions below.
(a).
使用者名稱 A
該使用者的公鑰 KUA
由 C A對 (A, KUA) 所簽署的簽章
(b). A[G], G[B], B[C], C[E], E[F], F[G]
8. Use flow-chars to explain the RSA signature with hash function H.
(a).
(b).
9. What is "Blind Signature"? Use flow-charts to show RSA blind signature applied in an electronic voting.
What is "Blind Signaure"? 簽名者在簽名時看不到文件
Use flow-charts to show RSA blind signature applied in an electronic voting.