632 views

### Why is appending the key to a mesage and then hashing that insecure if the hash isn't weakly collision resistant? [duplicate]

Suppose I have H(M|K) and that H is not weakly collision resistant. If I have a message mac pair (M,MAC), how is it possible to find another message mac pair (M2,MAC2)? My thinking for this problem is ...
120 views

### Can I use SHA (message || key) as MAC? [duplicate]

One should not use SHA for MAC, because knowing SHA(key || message) and message you can construct ...
116 views

### Why don't we use H(m||k) as a MAC? [duplicate]

HMAC seems a bit complicated. Why can't we use $H(m||k)$ as a MAC? Unlike $H(k||m)$, length extension attacks won't work. Is there some other obvious attack?
56 views

### Secret key suffix vs HMAC [duplicate]

What is the benefit of using HMAC over hash with key suffix? I realize that using key prefix is a bad idea because it allows message extension attacks. When adding key as a suffix such attack ...
4k views

### Is HMAC needed for a SHA-3 based MAC?

HMAC does nested hashing in order to prevent Length Extension Attacks. Given that you use the SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that ...
4k views

451 views

### How secure is MD5 for one way authentication?

I have a server S1 with an Private String (PS) as an identifier shared with a server S2. Every 10 min S1 publish the hash value of PS+the current time which is used as public identifier (PI). Every ...

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