1 Why do MD4 (older), MD5, SHA 1 and SHA 2 require a padding of messages that are already a multiple of 512 bits 2 Suppose Alice, Bob, and Carol want to use secret key technology to authenticate to each other If they all used the same secret key K , then Bob could impersonate Carol to Alice(actually any three can impersonate the other to the third) Suppose instead that each had their own secret key, so Alice uses K A , Bob uses K B , and Carol uses K C This means that each one, to prove his or her identity , responds to a challenge with a function of his or her secret key and the challenge Is this more secure than having them all use the same secret key K (Hint what does Alice need to know in order to verify Carol's answer to Alice's challenge )

Question

1  Why do MD4 (older), MD5, SHA 1 and SHA 2 require a padding of messages that are already a multiple of 512 bits  2  Suppose Alice, Bob, and Carol want to use secret key technology to authenticate to each other  If they all used the same secret key K , then Bob could impersonate Carol to Alice(actually any three can impersonate the other to the third)  Suppose instead that each had their own secret key, so Alice uses K A , Bob uses K B , and Carol uses K C   This means that each one, to prove his or her identity , responds to a challenge with a function of his or her secret key and the challenge  Is this more secure than having them all use the same secret key K   (Hint  what does Alice need to know in order to verify Carol's answer to Alice's challenge )

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1. Why do MD4 (older), MD5, SHA-1 and SHA-2 require a padding of messages that are already a multiple of 512 bits? 2. Suppose Alice,

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