2
votes
2answers
90 views

Linear Cryptanalysis - possible without plaintext?

If Linear Cryptanalysis exploits the fact that the plaintext and ciphertext are not completely unrelated, is the attack possible without having access to the plaintext?
2
votes
2answers
306 views

Breaking Double Encryption

I am trying to understand how an attacker knows when he has successfully decrypted a ciphertext for an assignment. As such, some pointers/hints for the following questions would be greatly ...
2
votes
1answer
205 views

Functional Encryption (for Non Experts)

I recently stumbled across "How to Run Turing Machines on Encrypted Data". Given that it's now possible to run turing machines on encrypted data, what open problems remain in the realm of Functional ...
2
votes
2answers
202 views

PRP, PRF and modular arithmetic

Are there any arithmetic or mathematical functions that can be used as PRPs or PRFs ? Since, Conventional block ciphers like AES are that are proven to be good PRPs are not based on mathematics but ...
2
votes
1answer
165 views

what's the advantages of identity-based systems over certificate-based ones?

Actually, I'm not familiar to how identity-based and certificate-based systems work, so ,can anyone give me a detail and comprehensive answer to this question? Moreover, in what environments the ...
2
votes
2answers
420 views

Json AES128: Security against known plaintext attack

I have a system where I am transmitting json messages securely (using for example AES-128), where each message has the same format. For example ...
2
votes
1answer
179 views

Distinguishing attack on CBC-MAC

I want to ask about distinguishing attack on CBC MAC, as in the paper published by Ketting Jia, Xiaoyun Wang, Zheng Yuan, and Guangwu Xu: Distinguishing Attack and Second-Preimage Attack on the ...
2
votes
2answers
99 views

Is this algorithm demonstrating “proof of work”

Is this algorithm demonstrating proof of work? This is a algorithm where a "token" is combined with a time stamp and then a cryptographic hash is generated from the combination, next the objective is ...
2
votes
1answer
102 views

What kind of Quantum cryptography technology(protocols) can be used for Mobile Ad hoc networks(MANETS)?

Typically ad hoc networks do not have a proper infrastructure and the routing is done only through the base stations which are connecting a wired and wireless network. Does quantum cryptography ...
2
votes
1answer
177 views

Is it possible to split a large AES encrypted string and decrypt the parts one by one?

Due to some platform restrictions our decryption algorithm can only handle up to 1 million bytes. The string we receive is larger, having been generated by AES in cipher block chaining (CBC) mode, ...
2
votes
2answers
145 views

Publicly exposed hash of private key

Would exposing a cryptographic hash function's digest (e.g. SHA-3) of RSA private key data compromise the key? If so, what are the possible (cryptanalysis-) vectors for attacking the key if an ...
2
votes
1answer
116 views

password generation: random length or max length

In short: Is it cryptographically stronger to have a known length password of the maximum length allowed, or a random length password somewhere in the range of the longest length possible? Does the ...
2
votes
1answer
208 views

Why is this MAC based on secure PRF with ordering and randomization insecure?

Is this MAC secure: To authenticate a message $m=m_1||\ldots||m_l$ where $m_i \in \{0,1\}^{n/2}$, choose $r \leftarrow \{0,1\}^n$ at random, compute $$t:=F_k(r)\oplus F_k(\langle 1\rangle || ...
2
votes
2answers
348 views

How should we interpret the cryptanalysis results of SIMON and SPECK?

The NSA recently released SIMON and SPECK light weight block ciphers. Although initial spec release did not have much of cryptanalysis details, two works later appeared providing the cryptanalysis for ...
2
votes
1answer
302 views

LFSR using words

If I've got an LFSR, let's say a 16-bit Fibonacci LFSR as shown in the corresponding wikipedia article, which generates maximum length sequences, could I use it to create word sequences instead of bit ...
2
votes
1answer
96 views

How do these figures represent a boolean function?

In the Wikipedia article "Bent functions", there are some figures representing those Bent functions: How do these figures represent a boolean function ?
2
votes
3answers
193 views

Decryption possible only within a period of time

Time-locked encryption and time-released encryption seem to be security systems focused on making sure that the decryption of certain message cannot take place before a certain time has passed. ...
2
votes
3answers
157 views

How should I interpret this note on diffusion of the internal state of a PRNG?

This question is about Tyche, a non-cryptographic PRNG. While the PRNG is not cryptographic the analysis and this question surely is heavily involved with cryptography, so I think it's on-topic here. ...
2
votes
1answer
558 views

Why does second pre-image resistance imply pre-image resistance

I am studying hash functions. I can understand why collision resistance implies second preimage resistance, but I don't get why second preimage resistance should imply first preimage resistance. ...
2
votes
2answers
244 views

Could completely public passphrase hashes ever be reliably secure?

This is a hypothetical question and I only have a basic understanding of Cryptography. If one were to follow the very best cryptographic practices for storing passphrases, could it ever be possible ...
2
votes
3answers
322 views

Can I dynamically calculate an appropriate number of iterations for PBKDF2 based on the system time, rather than using a fixed value?

Could you choose the number of PBKDF2 iterations based upon the system time? I've heard a few people recommend that the number of iterations for PBKDF2 should be doubled every two years (starting ...
2
votes
1answer
101 views

Recasting randomly generated numbers to other widths

Suppose I have a list of randomly generated uint_8's, uniform over the whole range of uint_8. I write them into a file as raw ...
2
votes
1answer
88 views

Is it possible to generate a message using the mac and the key?

Say that you have the Key and the MAC value that was generated from the Key using CBC. Is it possible to generate a message with just the mac and the key? If so, how would you do it?
2
votes
1answer
125 views

Can stream ciphers (usually) be “run backwards”?

Is it possible to reconstruct the previous output bits of a stream cipher, e.g. RC4, when only the current state is known, or is that computationally hard, or even impossible (due to ambiguous ...
2
votes
1answer
141 views

Security of cloud computational protocols in UC Framework?

The universal composability allows one to the analyze security of cryptographic protocols . But it does have some gaps when it comes to analyzing few protocols especially two party cases when there is ...
2
votes
1answer
140 views

Camellia cipher - is it a symmetric or asymmetric cipher?

I read a wiki page about Camellia cipher and know that it is a block cipher that can use 128-bit, 192-bit or 256-bit keys. But I cant find any information about if its a symmetric cipher (uses one key ...
2
votes
1answer
142 views

Public Keys on Social Media

Is there any problem with using social media (i.e. Facebook) as a directory of public keys? For example, couldn't Alice put a note containing $(g^a \bmod p, g, p)$ on her Facebook page so she could ...
2
votes
1answer
123 views

Can OTP still be broken if there are several messages being sent with only a slight variation in a password?

If an attacker were able to get a hold of 2 encrypted messages that were both encrypted in a one time pad with a password that were each similar but had one change in the first character, could it ...
2
votes
1answer
186 views

Why must we hash lot of times in rainbow tables?

I don't get the utility to chain and reduce in generating rainbow tables. Hash functions are made to not have collisions, or at least chain only 2 times so we don't return to the concept of the hash ...
2
votes
1answer
122 views

Can you explain what the AES paper means by “sharing active S-boxes”?

I am reading the "Biclique cryptanalysis of the full AES" paper. What do they mean by "sharing active S-boxes"? How can this concept can be advantageous to make a bicycle? If there is someone who ...
2
votes
2answers
170 views

Pseudorandom functions

The usual case to distinguish a pseudorandom function from a random function is to assume that the adversary can choose the plaintext blocks. Is there another case (game) in which the adversary can ...
2
votes
1answer
217 views

Are SSL modes with forward secrecy vulnerable to the BEAST attack?

From the original BEAST paper, it seems to me that you need the same session key when encrypting data, so you can check if the original plaintext block is the same as your chosen plaintext (which is ...
2
votes
2answers
156 views

No IV for one off symmetric file encryption

My question is (hopefully, for somebody) a simple one; but my project is holding as I'm not sure. I read on SO that generating encryption keys without an IV is a bad idea, so is using a constant IV ...
2
votes
2answers
217 views

HMAC and assumptions on the cryptographic hash

According to Wikipedia, a cryptographic hash function has the following properties: Pre-image resistance: Given $h$, it's difficult to find any message $m$ such that $h = H(m)$. Second pre-image ...
2
votes
1answer
257 views

How insecure in practice?

I am in attempt to understand relative insecurity of certain encryption schemes. Particularly of interest is DES and RC2. I know AES is better and should be used to encrypt. But practically, if ...
2
votes
1answer
541 views

Could quantum computers “break” symmetric crypto-systems (e.g. AES)?

These days I'm reading about quantum computing and quantum cryptography which I've found extremely interesting. Well, I also read some blog posts of Bruce Schneier talking about how quantum computers ...
2
votes
1answer
147 views

Is this algorithm secure?

I recently found this site, proposing a hashing algorithm for passwords. They describe the following: pad the password on both sides with SHA1(email) to ...
2
votes
2answers
776 views

Is Base64(SHA1(GUID)) still unique like the original GUID?

Basically what the title is; GUIDs are unique by design. If you run the GUID through SHA1 and then Base64 the hash, will the resulting string have the same guaranteed uniqueness as the GUID, or not?
2
votes
1answer
425 views

How does OAEP improve the security of RSA?

The heart of OAEP algorithm used for RSA encryption are the cryptographic hash functions $H$ and $G$. Does everybody (so also an adversary) know these functions? If YES: How does it help the ...
2
votes
1answer
238 views

What is a fair exchange scheme?

The Wikipedia entry Fair exchange has only two lines, and the only paper I can find describing such a protocol is extremely complicated. Is this a new field in cryptology or can someone give an ...
2
votes
2answers
230 views

Many consecutive hashes to slow down brute force attack?

I've heard that hash algorithms like bcrypt are more secure because they take longer to complete, and therefore take much longer to prute force, without a noticable ...
2
votes
2answers
555 views

risk of attacker decrypting RSA ciphertext without public or private key

As I describe in my previous question I am trying to decide if it's worth it for me to use the Offline Private Key Protocol in creating some long term private archives, instead of just going with a ...
2
votes
1answer
1k views

SHA256 HMAC brute force with chosen plaintext attacks

This is a follow up to Is It Possible To Reconstruct a Cryptographic Hash's Key I am using a SHA-256 HMAC function on a single-word input: sha256hmac(privatekey,word) = output. The private key length ...
2
votes
2answers
278 views

Why is $h(H, m) = E(m, H) \oplus m$ insecure?

I am taking a cryptography class on Coursera. I learned that the compression function $h(H, m) = E_m(H) \oplus m$ is insecure (even though other variants like Davies­-Meyer or Miyaguchi-Preneel are ...
2
votes
1answer
367 views

Attack on DSA with signatures made with k, k+1, k+2

For homework, I'm asked to find the private key, $x$, in a DSA digital signature scheme. In the particular instance, we are given the parameters $p$, $q$ and $g$, the public key $g^x$, 3 messages ...
2
votes
1answer
598 views

Brute forcing an HMAC

Given current technology such as GPUs and GPU cracking software I was wondering if anyone has an idea on how long it would take to brute force the key used to derive an HMAC?
2
votes
1answer
212 views

Proof of the standard pseudorandom generator + XOR encryption scheme in Goldreich

Reading Goldreich's Foundations of Cryptography II, I found this proof for the security of the common pseudorandom generator + XOR encryption scheme (Proposition 5.2.12 in the book): Assume you ...
2
votes
1answer
116 views

Padding always the same, problem or not?

I need to transmit long encrypted messages to a smartcard over a limited capacity link so I need to fragment the messages somewhere before sending thzm. My problem is that I split the message into ...
2
votes
2answers
439 views

What are the differences between proofs based on simulation and proofs based on games?

what are the main pros and cons of proving the "security" of a crypto scheme under simulation proofs instead of game based proofs?
2
votes
2answers
293 views

Is there a length-preserving encryption scheme?

Is there a length-preserving encryption scheme, that preserves the lengths of input sizes such that the length of the input plain text is same as length of the output cipher text ?

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