1) Consider the following authentication protocol:
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Client
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Transmission
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Host
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Explanation
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U, user
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U à
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I am user U
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ß {n, DES, SHA-1}
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n, random challenge, DES, SHA-1
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- I have SHA_1(P(U)), where P(U) is password of user U
- Here is a random challenge n, please use DES and SHA-1 to generate a response
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r=DES(n, SHA-1(P))
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U, rà
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Response r is the encryption of the hash of the password P of user U using key n, DES for encryption, and SHA-1 for hashing.
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ß yes/no
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Compare: DES-1(n, r) to SHA_1(P(U))
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Can the password of user U be obtained by using an offline password guessing attack? If your answer is yes, describe the attack and write pseudocode for the password guessing algorithm. If your answer is no, describe why the protocol is resistant to an offline guessing attack.
2) Using RSA, perform an encryption then a decryption of the message M=5 using p=3, q=11, and e=7. (please add explanation, Show all your work, not just the final answer.)
3) You are the designer of a password security policy that requires passwords to expire once they have a probability of 0.001 of being guessed. A potential attacker can test 1,000,000 passwords per second. If you chose passwords to be alphanumeric ("A" through "Z", "a" through "z", and "0" through "9"), what would you have to set the maximum lifetime of a password to in order to meet the required guessing probability (represent in days)?Assume the password size is 9 characters.