1
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3answers
415 views

Can we construct fully homomorphic encryption scheme based on non-circuit approach?

At present, all FHE scheme are be constructed based on circuit approach. Can we construct fully homomorphic encryption scheme based on non-circuit approach? Is Polly cracker non-circuit approach ?
1
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1answer
351 views

Can iterated key expansion in Blowfish slow down bruteforce attacks on small key sizes?

Suppose I have to use 64-bit keys for encryption (e.g. to comply with export restrictions). For this question, assume this key is truly random, and the encryption algorithm is Blowfish. Blowfish key ...
1
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1answer
594 views

Cryptanalysing Affine cipher

I am trying to cryptanalyse a cipher–text encrypted by Affine cipher. The encryption formula is: $c = f(x) = (ax+b)\bmod m$, where $a$ and $b$ are unknown constants; $x$ is a plain-text symbol, and ...
1
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1answer
131 views

Random decomposition of symmetric key

Considering a symmetric cipher (i.e : AES in counter mode), is it possible for any given key to be randomly decomposed into other keys without knowing the message or the ciphertext, such as : ...
1
vote
1answer
549 views

What would be the most effective way to brute force a 16 char AES key?

I have a file that is encrypted in AES using a 16 char string. The string is (a-zA-Z0-9) and .,?!. Also, it only contains words ...
1
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1answer
433 views

Other than brute force, are there any attacks on Threefish-512 using only a single known plaintext block?

As per title, other than brute force, are there any attacks on Threefish-512 using only a single plaintext block? Are there any attacks like this in any other cipher?
1
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1answer
429 views

RC4 S-Box and Keystream

I'm studying the RC4 algorithm and I have the following questions: On all questions assume that an expanded (2048-bit) key is used, and that the first 4096 bytes of the KeystreamIm are discarded. ...
1
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1answer
599 views

OpenPGP Public-Key Encrypted Session Key Packet Key ID generation

Im probably just not reading something again, but: RFC 4880 says that a OpenPGP Public-Key Encrypted Session Key Packet (tag 1) is made up of ...
1
vote
3answers
561 views

Does the MixColumns step come before or after AddRoundKey in AES decryption?

I found these images depicting the AES decryption process: In the first image, the MixColumns step comes before the AddRoundKey step, while in the second image, the AddRoundKey will come before ...
1
vote
1answer
110 views

Determine complexity of a SAT problem

Is there a standard way to determine a complexity of the specified SAT problem? I'm researching algebraic cryptanalysis and came to solving multivariate quadratic equation systems using CryptoMiniSat. ...
1
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1answer
162 views

Is it possible take a piece of data in secret?

I want something like this, but in a digital sense: You and others walk into a room. Everyone knows who each of you are and everyone is doing their best to figure out what piece of paper each ...
1
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1answer
333 views

Which encodings have |encoding key| >> |decoding key|?

I'm looking for an encoding scheme that requires a very large encoding key E (>10MB) and suffices with a relatively small decoding key ...
1
vote
1answer
208 views

Block ordering and security in a MAC?

To authenticate a message $m = m_1 \,\|\, \dots \,\|\,m_n$ the tag $t := F_k(r) \oplus F_k(m_1) \oplus \dotsb \oplus F_k(m_n)$ is used, where r is uniform random number $(0,1)^n$ and $m=(0,1)^n$. Even ...
1
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1answer
249 views

Is the SILC protocol still used? [closed]

I'm looking into implementing a private SILC server for friends (and possibly their friends). And after visiting the Wikipedia entry for SILC protocol, it seems all the official pages linked at the ...
1
vote
0answers
10 views

Source for PKCS#11 Header Files

Is there a known authoritative source for the ANSI C header files for PKCS#11 Cryptoki? Specifically, I am having trouble locating pkcs11.h, pkcs11t.h, and pkcs11f.h for v2.30 and v2.40. Are there ...
1
vote
0answers
23 views

Machine readable, user non-readable - XML file [migrated]

I need some advice as I have been unable to find anything useful via the web - (Google search). I have used the application EventGhost so as to create a custom shell, that I run using the Windows 7 ...
1
vote
0answers
17 views

RSA Signature Forgery

We all know that x509 certificates carry a signature that represents the certificate digest encrypted by the private key of the issuer. I believe that the digest is encrypted only providing one ...
1
vote
0answers
12 views

Logjam-style attack on Factoring?

We're all aware of the Logjam attack, which is known as "FREAK on discrete logarithms". Now the attack works by doing a large pre-computation step, which needs only to be done once per field and then ...
1
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0answers
29 views

HMAC for encrypted authentication token: recommended iteration number [duplicate]

In the web application I use 10,000+ iterations for hashing passwords stored in database (random salt and all). Password-related operations are not frequent enough to create a noticeable performance ...
1
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1answer
41 views

How is wpa2 authentication structured

I would like to understand the cryptography behind Wpa2. As far as I know, there are 4 messages on the 4-way handshake and three of them are values concatenated with hashes. First, I am trying to ...
1
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0answers
23 views

Determine safety of exercise hash functions

There have been several attacks against hash functions such as $h_{sha1}$ and $h_{md5}$. Professor A suggests a new function $h_{666}$ with an output length of 666 bits. Professor B suggests ...
1
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1answer
33 views

Determine if encryption is safe against CPA

The following encryption scheme encrypts each block of length $n$ of the plaintext separately: $c_i = k_1 \oplus F(k_2 \oplus p_i)$ Where $F$ is a strong pseudo-random permutation (i.e. it is easy ...
1
vote
1answer
52 views

Collision or second preimage for the Chacha core?

Daniel J. Bernstein's ChaCha core is an evolution of the Salsa20 core. Both are functions over the set of 512-bit bitstrings, partitioned as sixteen 32-bit words. Can we exhibit collisions, or ...
1
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1answer
42 views

Session key Exchange, some doubt

I have to find a solution to this problem: I have a network composed by 1 server and some client. The server has a couple of keys (public and private) and it shares a secret key with each client. My ...
1
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0answers
19 views

Compromised Issuing CA [closed]

I'm configuring a PKI infrastructure with an offline root CA and several issuing CAs. Among other topics, I'm struggling to decide how the revokation of an Issuing CA certificate works. My Root CA ...
1
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0answers
28 views

Voting protocol - How many dishonest tallying centres can the protocol cope with?

We have the voting protocol that is described here. I am looking at the following exercise: Determine how many dishonest tallying centres the protocol can cope with before the following properties ...
1
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0answers
29 views

Digital signature in a group chat scenario?

I understand that RSA is great for 1-to-1 digital signature. In the group chat of N people, other than storing and maintaining N public keys, is there a simpler way of authenticating each and everyone ...
1
vote
3answers
145 views

How to quickly detect incorrect password in encrypted file without compromising security?

I am developing a software to encrypt/decrypt files/streams using symmetrical encryption algorithm. During encryption phase data wil be compressed and encrypted. When decrypting data, I want to be ...
1
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1answer
69 views

Is there a scheme that allows to use RSA based challenge response protocol limited to signing only 8 bytes to create a secure signature of any data?

I have a tiny device that has a challenge-response authentication mechanism where the device signs 8 bytes of any data with it's internal 2048 bit RSA key. I would like to be able to certify any data ...
1
vote
1answer
36 views

Deriving 2 shared secrets from one private key and 2 different public keys

I have a key pair, say $(d, Q)$. I send my public key $Q$ to 2 different people. I also get their public keys $Q_1$ and $Q_2$. Now I can derive 2 shared secrets, $d*Q_1$ and $d*Q_2$. The 2 other ...
1
vote
1answer
39 views

sha256_hmac for session keys using a counter

I need to generate some session keys from a master key that was generated from an ECDH key exchange. The master key is 256 bits and I need 256 bit sessions keys. Is it safe to use SHA256_HMAC with ...
1
vote
1answer
42 views

How hard is it to recover $p$ if I can get $h(p) \oplus h(p^*) \oplus r$ and $h(r)$?

Assume that $h:\{0,1\}^* \rightarrow \{0,1\}^\lambda$ is a cryptologic hash function, $r$ is taken randomly from $\{0,1\}^\lambda$, $p$ is a low-entropy password and $p^*$ is a guess. Now we get ...
1
vote
0answers
24 views

Correlation attack on Lagged Fibonacci Generator

Say that one uses a known LFG (2 known lags $a$ & $b$, known inner state length $N$, known modulo $m$) to hide some text with a basic à la Vigenère cipher: $C_i=(P_i + {PRNG}_i) \bmod 26$. Say ...
1
vote
3answers
80 views

Is it possible to encrypt a message's destination as well as its content?

I have imagined a way to break through any kind of censorship but since I don't have enough professional knowledge of cryptography I don't know whether it is feasible or not. If there is a method ...
1
vote
0answers
46 views

Secure content-defined chunking

I am writing an app that needs to split a stream of plaintext bytes into variable-sized chunks (for deduplication). The way this is traditionally done is using a rolling hash function defined over ...
1
vote
0answers
53 views

Lightweight hash function

I am researching about lightweight hash functions and I've got two related questions: What is the standard or requirement for a hash function in general to be considered lightweight ? Why can it be ...
1
vote
2answers
53 views

Secure Channel - Encryption and Decryption Keys For A Message

I'm currently reading Cryptography Engineering and in Chapter 7, the topic of secure channel is discussed. The channel described is using CTR for encryption. Below I include images with pseudo-code ...
1
vote
0answers
33 views

Why does OMAC2 exist?

The specification for OMAC has the following to say about OMAC2: For OMAC2, we adopted u−1 instead of u2 as Cst2. It requires one right shift to compute L· u−1 instead of one left shift to compute ...
1
vote
0answers
49 views

Non-interactive zero-knowledge proof for discrete logarithm without random oracle

Is there any non-interactive zero-knowledge proof for discrete logarithm without random oracle over the group $\mathbb Z_p$?
1
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0answers
50 views

Why is public key cryptography not widely used in governments? [closed]

Are there any practical limitations? Govt driving license, passport, SSN could be digitally signed making it easy for anyone to validate. They can have a qr code in them which can be easily validated ...
1
vote
0answers
41 views

Hardening of random number generators

Boxcryptor uses various CSPRNGs and apparently hashes the output using PBKDF2 to derive the final key. Even though the choice of ...
1
vote
1answer
45 views

Attacking CBC with predictable but encrypted IV

Let P be a secure block cipher, eg AES-128. Let's say a server has a CBC encryption oracle which uses an attacker-selected yet unique nonce to generate the IV for each message = P(key, nonce). The ...
1
vote
1answer
33 views

Decryption of Huffman code

I know that Huffman is not a encryption method, but I have a bit-stream that I know it's Huffman coded. However, the tree/table that maps the codes to real characters is not available. Surprisingly, ...
1
vote
1answer
40 views

Are digital signatures using preprocessed paper pads possible?

My idea was, given that a computer could produce some sort of lookup tables on paper, could then a human use those lookup tables to create a system for digital signatures? This was really an idea for ...
1
vote
0answers
33 views

How do I verify a reset token if the token is hashed in DB?

I've been searching around the web for best practice how-to on secure password reset system (email with reset url), and the idea to hash the token in the database, which I did not implement at first, ...
1
vote
1answer
97 views

Calculating XOR Key Sizes

I've been playing around with the Matasano crypto challenges (cryptopals.com). I had a couple false-starts on the challenge that has you creating a program to calculate the key size of a XOR encrypted ...
1
vote
0answers
39 views

Commitment scheme to share money

I have such problem: party $X$ has an amount of money $M$, which it needs to share with $n$ other parties. Every week the amount of money is different. Let say not, that I am a party A, which is one ...
1
vote
1answer
64 views

Recovering key length from transposition block cipher ciphertext

First of all I would like to say hello to all StackExchange users. So far I've been stalking the forum for some time, now it's time to leave the shadows. In my master thesis I'm writing about ...
1
vote
1answer
136 views

Generate a list of valid ASCII codes

I have read many pages about encryption but I am really stuck on this. For access control to a building I want to print a 10 character ASCII code on a ticket (as a barcode). The barcode reader ...
1
vote
0answers
47 views

Avoiding known plaintext attacks with an additional XOR-Layer

Can a cipher that is vulnerable to an known plaintext attack be made secure by adding an additional XOR-encryption? That is: suppose I have an (w.l.o.g. symmetric) encryption algorithm E were the ...

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