analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)

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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 ...
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318 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?
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39 views

Autocorrelation in Autokey

I know that Vigenère can broken using auto-correlation (as explained at cryptool-online.org). Now my question is: Why does this also work with autokey (tested it using crypttool)? To prove that I ...
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81 views

(n,n) Shamir secret sharing [duplicate]

In (n,n) Shamir secret sharing if n shareholders do not have the public values (X values) can they still obtain the secret with only Y values?
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18 views

Cryptography — with a semi-priveleged user in the middle — to prevent request-tampering with another server

I'm working on a chat server for a mobile app I am writing. I would like to use a different application server for non-chat related operations and another application for chat operations. I would ...
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175 views

Example of second preimage attack [closed]

Please, I'm trying to understand second-preimage attacks on cryptographic hash functions. I understand the definition well: given a message and it's hash, an attacker finds another message which ...
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149 views

Is there any analysis of freebsd's “geli” encrypted geometry provider?

I've done a few obvious searches on google and google scholar and not turned up any security analysis of FreeBSD's geli. Is there some out there, or has it gone unanalyzed since its introduction ...
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209 views

How good is the RandomPool generator in Crypto++ library?

How good is the RandomPool generator in Crypto++ library? I never heard of it before… I wonder if there is a Fortuna C implementation that I could use in an Objective-C project. Also: How secure is ...
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45 views

AES and Known-plaintext attack [duplicate]

Can you help me to finding some papers that shows AES is secure against known-plaintext attack?
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37 views

Computing A, B given A+K and B+K [duplicate]

In his writeup of the Solitaire keystream generator algorithm, Bruce Schneier warns not to use the same key for two different messages: The first rule of an output-feedback mode stream cipher, any ...
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86 views

Partial encryption of a file?

I want to partially encrypt a large block of data using AES. Meaning: given plaintext[0:1100], I would like to encrypt ...
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112 views

Cryptanalysis not based on method used to encrypt? [closed]

When doing cryptanalysis on RSA or something number theory based, there are various attacks that all seem to involve number theory (Wikipedia: RSA_(algorithm) ~ Attacks_against_plain_RSA). Similarly, ...
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105 views

Career advice for our readers [closed]

I am a first year math PhD student with work experience and an MS in math. Do you have any advice regarding internships involved with cryptography and other mathematics other than the NSA? Thanks.
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128 views

Differential Cryptanalysis of FEAL-4

I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall. Basically I attacked the final round first ($K3$) using the differential characteristic ...
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78 views

Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]

Possible Duplicate: Two untrusted party want to exchange data: how to insure each one gets the data it needs? I am trying to come up with what could maybe be a novel algorithm for an ...
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237 views

How secure would this code be against cryptanalysis?

Simple version: Create software that takes a database of the dictionary, alphabet, and phrases. Randomly generate a database of random strings of letters/numbers/symbols of varying length. Randomly ...
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215 views

Why are these techniques not feasible to crack RSA?

For $d = e^{-1} \mod \phi(n)$ $$d\cdot e \operatorname{mod} \phi(n)=1$$ $$d = (e^{-1} \operatorname{mod} \phi(n))$$ With having $e$ and $n$, we can calculate the value of $d$ , the private key for ...
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317 views

Is this encryption scheme perfectly secure?

Let $m = 6$, and let $\mathbb{Z}_m$ denote the set $\{0,…,m-1\}$. Let $X \mod m$ denote the remainder obtained when dividing $X$ by $m$. (a) Consider the symmetric encryption scheme in ...
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65 views

Key cracking: Prefer many small texts over one large text?

If an attackers sets out to crack the symmetric key of e.g. AES-CTR, would they prefer to have access to many small cryptotexts or one large cryptotext? I.e. is it more interesting for the attacker to ...
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312 views

Cryptographic Symmetric Stream Cipher

Let me know a cryptographic symmetric stream cipher system with only two functions say S() and P() and it should satisfy the ...
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431 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 ...
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95 views

Prime factors of non-random keys

I have been working on a challenge i found on the internet. It is as follows: You've stumbled onto a significant vulnerability in a commonly used cryptographic library. It turns out that the ...
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131 views

Partially-known-plaintext attack of a stream cipher based on modular arithmetic

I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ ...
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56 views

Bicliques for permutations

So I'm trying to understand the complexity of the biclique attack on Grostl and I have some questions: 1) The paper introduces sliced bicliques where on Grostl one constructs a biclique of dimension ...
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161 views

modfied man in the middle attack diffie hellman

I have been given a problem in preparation for my cryptography final that I'm not sure how to solve. It asks me to suppose a scenario where instead of where an attacker would intercept some message ...
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328 views

WIN LM Password Hashes (using John the ripper) [closed]

In a problem set, we've been asked to use John The Ripper to crack a list of Win LANMAN passwords. They are of the following form: 953A55E36AB85C0B9DA92C18555E42E1:0169295E0A6A6B35B2DD9932D10C1978 ...
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304 views

Chosen Plaintext Attacks against an Affine Cipher

Assuming the ability to launch Chosen Plaintext Attacks (CPA), how many oracle calls an attacker needs to break the affine cipher? and how
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203 views

What is the complexity of the Square attack against the reduced 4-rounds 128-bit Rijndael variant?

I'm looking at a square attack against a reduced version of AES-128 with only 4 rounds (with block and key size of each 128 bit). I have a set of 256 plaintext-ciphertext block pairs. What is the ...
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913 views

AES encryption for images [closed]

Why AES based encryption is not recommended for encrypting images with high redundancy in their content? for example, the encryption of an image which shows a bird in the blue sky. Most of the pixels ...
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2answers
122 views

RSA decrypting of a huge file by parts [closed]

I need to decrypt a huge file that I own previously encoded by myself with a RSA public key (it's possible for this step using a symmetric algorithm key). Problem is that I can't load it in my ...
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54 views

find $x$, given $\{c_ix = k_i + y_i\}_{i=[1,n]} $

Given $$c_1x = k_1 + y_1 $$ $$c_2x = k_2 + y_2 $$ $$\vdots $$ $$c_nx = k_n + y_n $$ where the values of $\{c_1 \ldots c_n \}$ and $\{ k_1 \ldots k_n \}$ are known, and $x, \{y_1 \ldots y_n \}$ are ...
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89 views

Is it possible to find plaintext from ciphertext if (n) and (a) are known for RSA?

I have a couple of questions pertaining to a RSA problem. I need to decipher some ciphertext and find out what the original plaintext was. Modulus: $n = 2537$ and exponent: $a = 11$ Encrypting ...
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68 views

How to decrypt a text which is ciphered same length key? [duplicate]

I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ...
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219 views

Blum-Blum-Shub Cryptosystem

I am given $N$, which is Bob's encryption key. I was able to successfully factor $N$ into $N=p*q$. Alice encrypts a messages for bob and sends $a = [1,1,1,0,0,0,1,0,1,1,0,...]$ $b = 1545164156...$ ...
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40 views

Merkle-Damgard transform: necessity of the Length block [duplicate]

The Merkel-Damgard transform append the message length (in blocks) to the message itself and then computing the 'chained hash' algorithm. Does the last block (which contains the length of the ...
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61 views

Strength of Combining Hash functions [duplicate]

If I combine two hash functions, what will the impact on the strength of the resulting function. If I combine in following way: H1*H2 (multiply) H1 + H2 (concat) H1 Xor H2 H1 (H2) EDIT: Lets say H1 ...
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272 views

Shamir Secret sharing - Can share generator keep x values secret?

I'm wondering, in Shamir secret sharing, can generator of the shares, keep the x values which are used in evaluating the polynomial to obtain y values (i.e., the shares) secret, and whenever the ...
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154 views

cryptography and use of python programming language [closed]

why is it recommended to write cryptography programs ,for example crypt-analysis projects with python programming language? what is the advantages of python? why not use c or any other language?
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123 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
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1answer
134 views

How do I cryptanalyze a password field?

In a PostgreSQL database, I can see the following fields in a table (for a specific record): User = administrator Password = "ceMv9Me6go" Now the following are true: The password length is not ...
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1answer
81 views

Reverse engineering a single checksum byte [closed]

I am working to understand a system which saves a few bytes of data together with what appears to be a single checksum byte that provides a very naive guarantee that the data has not been tampered ...
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1answer
111 views

How to determine which type of crypto is used in a text file? [closed]

is there a tool or a way to determine which type of crypto is used in this type of text: ...
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43 views

Which causes longer “break” time (in general)?

In general (if possible to determine) which would make an output harder to turn into plain text with a computer? Extreme Length (minor complexity change) Extreme algorithmic complexity (minor length ...
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54 views

Can anyone help me decrypt this? [on hold]

We were told that GREENENVY was a hint but I don't know how to do anything from there. AU/W/ACBXMSN/IEHOFIE/NZ
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40 views

Strengthening security of an encrypted file against forensic detection [on hold]

I have created a Truecrypt container for backup in the cloud, and I want to obfuscate to the greatest extend possible which software and algorithm was used to encrypt the data and to slow down any ...
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3answers
777 views

How can I find the prime numbers used in RSA?

I got this question in a local hacking event, but I couldn't solve it. Problem Statement ---- Continuing their snooping habit, NSA kept bugging Alice's communication. Resorting to the age old ...
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704 views

How to hack the new save encryption on ipad for uplink? [closed]

The new iPad version of Uplink appears to be using some newer saving mechanic than the PC/Mac version. Macs and PCs use the REDSHIRT format, but the iPad appears to instead be using ...
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693 views

finding collision for truncated SHA1 hash output

Suppose we truncate only 40 bits of sha1 hash output.hence it is insecure.how can we find two message as input which gives first 40 bits of hash as same value i.e we have to find collision for first ...
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1answer
132 views

ASCII Message in TV show? [closed]

So I was watching a popular series tonight (Person Of Interest) when suddenly during a frame change I noticed a very quick blue screen with writing. At the time I never thought anything of it as it ...
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96 views

Deciphering a Custom Encoding Scheme [closed]

I've been tasked with figuring out the strength of an encoding scheme developed by my employer. I've been given a thousand plain-text numerical values along with their corresponding numerical ...