# All Questions

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### Why does DSS have such formulas?

I've learnt the formulas needed for the DSA (http://en.wikipedia.org/wiki/Digital_Signature_Algorithm). But most importantly, I don't quite understand what represents those formulas and why they are ...
886 views

### Why use CBC-MAC? Why not just apply hash function on the whole message?

Why not just apply hash function on the whole message? Why convert that message into blocks and hash those blocks? To avoid collisions?
1k views

### Block Cipher vs Stream Cipher in Web Application [closed]

I'm doing research about "Cryptographic attack methods in Web Application" so I have some questions to ask you guys: Block Cipher vs Stream Cipher, which is more common used in Web Application? How ...
141 views

### No Birthday Attack to TCR

I'm reading the paper “Collision-Resistant Hashing? Towards Making UOWHFs Practical” , which compared TCR (Target Collision Resistant) and ACR (Any collision Resistant). It says we wish to stress ...
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Consider a secure modern block cipher like AES/Serpent/Twofish. I hear everyone say that the complexity is $2^{128}$ for a 128 block cipher. But isn't the weak link the actual hashed and salted ...
843 views

### RSA decrypt long messages (javascript)

I am attempting to encrypty/decrypt a long message in RSA using javascript (with crypto-js and jsbn libraries). I posted this on stackoverflow too but I figured someone here on crypto might be able ...
453 views

### Recommended authenticated stream cipher for minimum overhead?

I'm running my TCP/IP protocol secured by encrypting each packet with AES128/CBC, bundling a SHA256 HMAC over that packet. This causes quite a bit of space overhead for small packets, so at first I ...
301 views

### Proving HMAC collision probability bounds?

Could someone point to results or proofs about the probability of $$HMAC(k, m_1) = HMAC (k, m_2)$$ assuming the underlying hash function is SHA-256? Would those probabilities be higher/lower if $m_1$ ...
374 views

### Encrypting and Decrypting a 19-digits long BigInteger

How can I take a maximum 19-digits long BigInteger and encrypt it with the following rules: The result must be based on digits and lower-case English letters only....
208 views

### Is solving a modular linear equation a hard problem when the coefficient is not an invertible element?

Assume that we have a linear equation like this: $$ax=b \pmod n$$ when $x$ is the unknown, and $a$ is not an invertible element in $n$. is finding $x$ a hard problem? (by solving I mean finding an ...
552 views

### Properties of Ideal Straight P-Boxes

What properties should an ideal straight P-Box exhibit?
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### AES 128bit round level recommendation

we don't want change standard just after every attack, now for AES 128bit blocks i think 16 round is secure, but what is best round amount ? we had attack for 7 round then 10 round and it going so on ...
1k views

### Is the AES encryption scheme CPA secure?

Give a 256 bit key space and 128 message space would AES block cipher as the encryption scheme be CPA secure?
896 views

### detecting ROT13/base64 encryption

Is there anyway to detect that a cipher is encrypted with ROT13 Or Base64 without decrypting it using the algorithm and check that the result means (works)? I mean does an algorithm exists that test ...
4k views

### Is MAC better than digital signature?

MACs differ from digital signatures in the sense that MAC values are both generated and verified using a shares secret key. Does this in any way put MAC on a disadvantage as compared to digital ...
29 views

### In NTRU digital envelope, do everyone know the hash function $H$ used?

I have a simple question about the NTRU original cryptosystem using a digital envelope. The article can be found here: http://grouper.ieee.org/groups/1363/lattPK/submissions/ntru.pdf It is said that ...
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### private-key can't be traced (GPG)?

I am very new to cryptography. I was reading about GPG/PGP Basics, and I have a doubt: As per my understanding, Everyone knows the algorithm (GPG) with which I generated my key pair. And If I give my ...
40 views

### Is a KDF needed when using X25519 for ECDH and XChaCha20-Poly1305 for AEAD?

Is a KDF needed when using X25519 for ECDH and XChaCha20-Poly1305 or XSalsa20-Poly1305 for authenticated encryption? My hypothesis is "no" because the key from X25519 is less than 256 bits long; ...
91 views

### New Improved Probabilistic version of RSA

On the 2nd page of "New probabilistic public-key encryption based on the RSA cryptosystem" by Roman'kov (PDF), at last it says Alice can find "f" of order "l" with least probability of (1-1/l). I ...
49 views

### Security of AES CTR with multiple messages containing the same known plain text

I have this scenario: The same plain text (that is part of an unkown bigger message) is being ecrypted multiple times using AES 128 CTR with a random key, the key is being transfered encrypted using ...
47 views

### DROWN Attack - Which is the SSLv2 vulnerability exploited?

In order to get the session key used in TLS communication, an attacker must capture X TLS handshakes based on RSA key encryption, and switch to a server supporting SSLv2 protocol, and sharing the same ...
100 views

### Symmetric cipher speed (AES vs Camellia vs Twofish)

If I have understand correct, Twofish is more secure (harder to break) than AES and Camellia, but Twofish is slower than AES and Camellia. But how can I mesure the speed difference between AES vs ...
63 views

### Is AES-CTR or ChaCha20 vulnerable to a time-memory trade off?

Is AES-CTR or ChaCha20 vulnerable to a time-memory trade-off attack? According to this paper it seems to be, which would put AES-CTR at a clearly breakable $2^{64}$ security level (for AES-128-CTR). ...
162 views

### Is it possible to brute-force a hash algorithm of 32 bits

I have a 30000 user passwords and usernames stored in a table on a database in which the passwords are stored as hash where ,I need to guess the passwords for all users and I have the hash function ...
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### What is the typical block size in RSA?

If the input text is divided into a fixed block size for encryption and decryption, what could be the typical block size for RSA algorithm for different size of input like 8 MB, 16 MB, 126 MB and 256 ...