Encryption is the process of transforming plaintext using a cipher into ciphertext to make it unreadable to anyone except those possessing the key. Decryption is the process of transforming that ciphertext back into plaintext, using the key.

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Cipher built from GPU primitives [closed]

Is it feasible to build a cipher (or hash) out of GPU or DSP primitives (e.g. big matrix multiplication, Fast Fourier Transform, big block SIMD, or hardware H.264/AVC codec)? Preferably those are slow ...
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RSA-KEM construction

"Create a random key for CCPA2 scheme, encrypt m, send it along with a PK encryption of the symmetric key. " Say in the process, the KDF is HMAC, then: get a random key (128-bit) C1 = encrypt ...
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RSA encryption and signature padding flaw

This is Oxford's computer security exam question: Suppose that Bob has published an RSA encryption key $ke$ (retaining in secret the corresponding decryption key $kd$), and Alice has published a ...
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501 views

An example of Knapsack Cryptosystem cracks/attacks? [closed]

I have been studying papers on various ways to crack the knapsack cryptosystem, unfortunately the mathematics in these papers involves lattices and LLL which is over my head. The paper "New Attacks ...
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Machine Learning with Encryption [duplicate]

Machine Learning is sometimes associated with cryptography. Many of such cross field studies have been majorly done in use of machine learning for cryptanalysis/decryption. I am interested in knowing ...
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194 views

File Encryption (EFS method)

I'm implementing (for learning purposes) a file encryptor, which uses the following method (from http://en.wikipedia.org/wiki/Encrypting_File_System). I have 3 kind of keys: RSA public/private, AES ...
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how to truncate a PRF on n bits to PRF on t bits where t < n? [closed]

Dan Boneh's courersa lecture on format preserving encryption at 5.50 mins , talks about truncating a PRF on $n$ bits to PRF on $t$ bits. The approach is by appending $(n-t)$ zeros to input $t$ bits ...
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1answer
280 views

Bellovin 96' attack on IPsec ESP protocol on encryption only option

Can you explain the actual attack? Why does the attacker need to firstly send some arbitrary UDP packet? How can the attacker break the privacy between A and B? Link: The article of Bellovin I'm ...
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122 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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766 views

How do I enable AES-NI (hardware acceleration) for Node.js crypto on Linux? [closed]

I wrote a basic function to test the speed of the AES-256-CBC mode of the Node.js built-in crypto functions. These functions use OpenSSL, so they should support AES-NI, but when I correctly enable ...
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137 views

Ideal system for an encryption scheme

What is the ideal system for an encryption scheme? For a pseudorandom permutation the ideal one is a random permutation, for a pseudorandom function the ideal one is a random function. For an ...
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93 views

Is this any recognizable encoding or cipher? [closed]

I've been watching the Marble Hornets videos on YouTube (basically, an independent film series about a group of kids chased by the "Slender Man"), and in this video I saw something interesting. ...
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How well analyzed are giant block length ciphers?

I have heard about ciphers that have a block length of 256 megabytes... That is huge. How well are they understood by the encryption community? I'm referring to PMC Ciphers. Has anyone used such a ...
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175 views

How can I prove that this encryption scheme from a random oracle is secure?

I am reading this example: A random oracle is an ideal object. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
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1answer
204 views

Messages of different lengths and one-time computationally-secret

I'm preparing myself to exam, but I have a lot of troubles with rigorous proofs. Let $\Pi=(Gen,Enc,Dec)$ be an efficient secret-key encryption scheme that is not fixed-length. That is, for any $n$ ...
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2answers
244 views

How to construct a variable length IND-CPA cipher from a fixed length one?

Suppose we can construct a secure (IND-CPA) encryption scheme for fixed length messages. I was wondering if there is a natural way to extend this construction for messages of variable length such that ...
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201 views

How do I encrypt with the private key? [duplicate]

Possible Duplicate: RSA encryption with private key and decryption with a public key This wording is creeping everywhere (e.g. there): "I encrypt with the private key" and even sometimes, ...
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1answer
76 views

How to construct the blind factors in practice?

I'm Implementing a protocol that uses masking techniques (or blinding factors), so we can mask a value $y_0$ as $m_0=y_0 \cdot r_0$ where $y_0 \in \mathbb{Z}_p$ and $r_0 \stackrel {R}\leftarrow ...
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310 views

Reordering non-block-aligned parts with DES in ECB mode

I was given a ciphertext file which was encrypted using DES in ECB mode. It is known that the plainttext that was encrypted has the following form: Each line of text consists of a payroll followed ...
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2answers
390 views

P10 to P8 in S-DES

I am new to cryptography. During my learning I am facing a problem with S-DES. I am confused where P10 to P8 come from, and I’m ...
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3answers
787 views

random access stream cipher

Some time ago I was working in a pet project for a type of database engine. And I thought about securing the data in disk with encryption.. and since the main code was already developed.. I had a few ...
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2answers
1k views

Custom crypto library in C

I will be making (in the near future) an app that will contain some pretty heavy crypto. As it is possible that my app will be ported to different devices (initially it will be iOs only, but Mac, ...
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“Padless” One-time-Pad encryption

I have just read about the perfect security of an OTP encryption and what came to my mind was that what if the Pad used for encryption/decryption did not have to be transported separately from the ...
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Which attacks can be avoided by the use of OFB instead of ECB?

For a file encryption program, I was told to use Output Feedback mode (OFB) instead of ECB (Electronic code book) mode. Which attacks can I avoid by this choice?
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Is it safe to use XOR to encrypt data key using master key

I am implementing a hierarchical key system with a randomly generated master key and many randomly generated data keys that should be encrypted using the master key. I am wondering what the best way ...
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84 views

Concerns about use of MAC in my specification

Here is the pseudocode for a routine I am designing: ...
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1answer
240 views

Is encryption time greater than decryption time?

Is encryption time always greater than decryption time for all encryption techniques (AES / DES / RSA / DNA), or is there a mistake somewhere in my implementation?
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ElGamal: Generation of “g” value?

I haven't been able to find a clear explanation on this (and I'm probably just confused in general). I have the following parameters of ElGamal signatures: $p$ = safe prime $q = (p-1)/2$ $g$ = an ...
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283 views

Message exchange with textbook RSA

I am working on this exercise but can't work out the answer to the question b. I have solved the question (a) by decrypting the ciphertext $C = 2$ using the formula: $$ M = C^d \bmod n = 2^{17} \bmod ...
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193 views

What is “msg = group.random(GT)” in Charm encryption schemes?

In many encryption schemes in Charm the random group message is used instead of a text-message: msg = group.random(GT) For example, in CP-ABE scheme, random ...
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Theoretical security of bit rotation for encyption

This is a theoretical question. I have a idea, encryption by bit rotation in byte. Do not know if something like this already exists. General concept is: First n bytes is rotated to left or right ...
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1answer
83 views

If you encrypt an image (AES), is it still an image and can you view it?

Can you encrypt an image (with AES) such that you can open it as a png/jpeg?
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180 views

Determining if a ciphertext can be decrypted

I want to know what the state of the art in the following cryptographic problem is. Assume a public channel on which encrypted messages are exchanged, using symmetric key encryption. I hold a couple ...
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254 views

Prove that if we redefine the key space, we can assume Gen chooses a key uniformly

I am working on problem 2.1 in Introduction to Modern Cryptography 2nd edition by Katz and Lindell. 2.1) Prove that by redefining the key space, we may assume that the key generation algorithm ...
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What cryptanalysis is possible against two independent keystreams XORed against plaintext?

If a wise person was unsure about which commercial cryptography standards are truly secure from the fascist powers that be, it would seem the obvious option for companies and individuals is to now use ...
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How does TLS generate the shared secret?

From many readings, I got to know that TLS generates master shared secrets using pre-master keys and uses the DH algorithm to generate the shared secret/Master secret. What values during the hello ...
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1k views

Generate fixed length cipher text from arbitrary length plaintext

Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes?
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Initialization value (IV) bit error

When a bit error happens in an IV, what would the result of decrypting a cipher-text be in the different encryption modes like ECB, CBC, CFB, OFB, and CTR?
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How can encryption involve randomness?

If an encryption algorithm is meant to convert a string to another string which can then be decrypted back to the original, how could this process involve any randomness? Surely it has to be ...
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suggestions for cryptography projects for an ece 3rd year student

I am an electronics and communication engg student currently doing my 3rd year second semester. i am interested in info coding and the security aspects of it. As an ECE student i want to know what is ...
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81 views

Why is RSA encryption version 1.0 not specified in an RFC?

I saw that there are three RSA encryption versions, as follows: RSA encryption version 1.5 (RFC 2313) RSA cryptography specification version 2.0 (RFC 2347) RSA cryptography specification version 2.1 ...
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135 views

Is there a way to encrypt an integer within an arbitrary range?

I need an algorithm that can take an integer, an arbitrary range, a key of 16/24/32 bytes, and an initialization vector of 16 bytes(ideally), and return an integer in the same range. My latest attempt ...
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162 views

Basic Encryption and Decryption related question

I recently started studying cryptography and got interested in the subject. But I got this doubt when I was studying the encryption scheme. Even though we encrypt our message and change it into ...
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92 views

Which data encryption mechanism to use for data transfer?

I have high performance nodes communicating with each other sending logs and data over network. The communication is heavy and over public network. I would like to know how to know which is the best ...
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92 views

How much pre-hashing a password increase security against brute force attack?

I am wondering how much hashing a password used as key for a symmetric key algorithm helps preventing brute force attack on crypted text. Let's assume I want to crypt text A using key B using ...
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Can AES be considered as Perfectly Secure?

I am studying about the AES encryption standard, and as I know from the theory there is no known weaknesses today about this block-cipher. I would like to find out or at least to understand what ...
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139 views

Can I use the output from a DRBG directly as K for AES, or do I need to use a key generator algorithm?

NIST has 3 validated "Recommendation for Random Number Generation Using Deterministic Random Bit Generators" (DRBG's) that are based on NIST SP 800-90A: Hash_DRBG (based on hash functions) ...
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136 views

How difficult is it to get a key using simple XOR

Recently someone gave me an algorithm as follows: XOR = Key XOR Random1 XOR Random2. They think that in order for someone to extract "Key" from XOR they would need Random1 and Random2.. but looking ...
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334 views

What is the period of a cipher?

For the following explanation of RC4: It is a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. Analysis shows that the ...
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225 views

Number of keys for a monoalphabetic cipher

My teacher stated that… The number of possible keys (E) in a monoalphabetic cipher is $26$! My thinking: Every letter in the alphabet can be $25$ different letters hence it the number of ...