Linked Questions

2
votes
0answers
50 views

Will length-extension work if secret is not prefixed but appended to the data? [duplicate]

Possible Duplicate: Why is h(m||k) insecure? Length-extension allows to append any data to the message while not knowing the secret. Any length-extension explaination one the web considers the ...
49
votes
2answers
13k views

Why is $H(k\mathbin\Vert x)$ not a secure MAC construction?

If $H(m)$ is a secure hash function, can't we implement a MAC using $H(k\mathbin\Vert m)$? However, it seems the more widely used MACs, such as NMAC and HMAC (both originally defined in Keying hash ...
20
votes
3answers
3k views

Attacks of the MAC construction $\mathcal{H}(m\mathbin\|k)$ for common hashes $\mathcal{H}$?

Consider a common practically-collision-resistant hash function $\mathcal{H}$ (e.g. SHA-1, SHA-256, SHA-512, RIPEMD-160), perhaps based on the Merkle–Damgård construction as are the first three. We ...
9
votes
4answers
484 views

Using hashes as passwords

I have thought of a system for generating passwords which works as follows: Take the following items: A password, such as williamwallace. A secret 1000 digit ...
1
vote
3answers
607 views

Understanding MACs and why cleartext is sent over

Assume both Alice and Bob have a symmetrical key, let's call it $k$. They agree on a cryptographic hash function, let's call it $\mathsf{HASH}$. Now Alice wants to send an authenticated message. She ...
5
votes
2answers
1k views

Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?

Given that we know that nonce + message + hash(nonce + message + mac-key) all inside the encryption makes it possible to detect if any bits of the message have been ...
2
votes
1answer
2k views

Reversing SHA1 (don't know the correct term)

Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))? pad(A) means its length is exactly 1 block (64 bytes for SHA-1) If yes, for which other hash functions it will work too? ...
-3
votes
1answer
145 views
2
votes
1answer
63 views

Constant data as input to hash

I want to use hash function on some data, and part of this data, might be constant for a certain period. The output of the hash function is used as authentication data (MAC). I want to know if there ...
1
vote
0answers
26 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 ...