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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In S/MIME, are the same certificates always used to sign and encrypt messages?

My assumption is that S/MIME almost always utilizes certificates as follows: My certificate can be used to allow people to encrypt messages and send them to me. My certificate (the same ...
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118 views

Diffie-Hellman for Encryption

In learning how DH works for cryptography applications, I'm coming across some confusing language. For starters, most of the time DH is discussed in the context of "generating" their shared secret. ...
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AES column mixing and S-Box confusion

I am trying to understand the AES encryption algorithm. I know that we process 128 bits at a time for a 128 bit key in a 4x4 octet form, but am confused by the following: How does the substitution ...
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Determine the Key given ciphertexts and plaintexts?

Given two sets of plaintexts and their corresponding ciphertexts, how does one determine the key $K$? The ciphertexts are: $$C_1= (P_1 \oplus K_0) + K_1$$ and $$C_2= (P_2 \oplus K_0) + K_1$$ $K = ...
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377 views

Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?

I'm writing my own cryptosystem that uses One Time Pad and Diffie-Hellman to generate keys for the OTP. I am using Rails on the server side and Javascript for the client side. Please don't tell me ...
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PRP representation size

I'm now studying the block cipher substitution-permutation network construction and realized that it uses several small pseudo-random permutations instead a big one for saving memory (or that is one ...
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249 views

Can you help me with this DES variant analysis?

I'm struggling with some DES variant that I got as an exercise (exercise taken from Katz-Lindell Ex5.14). The variant is as follows: The left half of the master key is used to derive all the sub-...
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274 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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Increasing the diffusion of the AES-CBC encryption algorithm in pycrypto for python

When encryption is done using the AES-CBC algorithm, the encryption can be thought of as chaining the cipher texts with the previous ones and an IV. However, if its on CBC mode, we give our cipher ...
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247 views

How do we arrive to the equation for solving D in RSA?

We have been shown that DE is congruent to 1 mod phi(n). How do we arrive to the real equation for figuring out d that is d = e^-1 mod phi(n). I want to know the entire process. I am just curious, ...
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Using the same RSA keypair to sign and encrypt

The RSA signature operation is basically the same as encrypting with the private key. In particular, both operations use the same kind of keys. Is it safe to use the same RSA keypair both for ...
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338 views

XOR cipher Pseudo-random key strength

When implementing a XOR cipher with a pseudo-random key equal in length to the plaintext, Is there a significant difference in potential key strength between keys drawn from a pool of either 1000 or ...
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332 views

Ciphers in CBC mode reveal place of change in plaintext

Theoretically, when using a symmetric block cipher in CBC mode, the current block is dependent on the previous block. Suppose one plaintext is encrypted using CBC, and then one bit of it is changed, ...
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336 views

Shamir's Simple Sharing Scheme - preventing partial recovery of data

In SSSS, if you recreate the original secret with one of the decoder inputs being slightly damaged (e.g. one or two chars incorrect), you receive a slightly damaged version of the original secret. So ...
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239 views

Is the following symmetric design secure?

Assume: $O$ be a reversible random permutation oracle on a finite set and $O^{-1}$ the inverse permutation (pretty much equivalent to a random permutation: What is the difference between a bijective ...
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Is CBC really dead?

I developed a p2p-app in C# which sends and receives encrypted text messages (50KB). For encryption, my app uses AES 128 bit in CBC cipher mode. For each message it uses a new randomly-generated IV. ...
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How to obtain KCV from the key

Simple question: we have AES 128 encryption and a key. How can we calculate the key check value (KCV)? One example: key is 48C3B4286FF421A4A328E68AD9E542A4 and KCV should be 77DC84. I am trying it ...
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180 views

Help me about Advanced Encryption Standard (AES)

Suppose $E_k$$(a, b, c)$ is encryption of values $a, b$ and $c$ with key $k$ through encryption algorithm AES (AES-128) and each $a, b$ and $c$ are 300 bits integer values. Also Suppose this ...
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What scheme will allow merging and splitting the result of a function?

I am wondering if it's possible to have a scheme as follows. Here is the scenario: we have a set of objects (e.g. strings) {O1, O2, ..., On} we have a set of users {U1, U2, ..., Um} each user asks ...
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62 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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136 views

Creating a secure key

Imagine that your lecturer and the undergraduate office have conducted a key exchange protocol after which both of them hold the string $X$. Yet, it is possible that a curious student sitting next to ...
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175 views

Encoding multiple fields with same AES key and vector?

I'd like some advice on cryptography best practices. I need to store on my web app the users' credentials (login & password) for 3rd-party sites. I'm using AES-256 with random key and ...
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189 views

Authentication of machine before installation (to stop piracy) [closed]

I have a web-software project which needs a bit of protection in form of authencitation… This web based software runs on an intranet. There is no access to the internet from these terminal machines. ...
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758 views

Is CBC mode encryption vulnerable to a reordering attack?

I know that, if CBC-MAC is used in such a way that the tag is the concatenation of all the blocks' outputs (and not just the last one), it's insecure under CPA for the simplest case of 2 blocks CBC-...
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Why can we always assume that $Gen$ algorithm choose key uniformly?

Talking about a (symmetric) encryption scheme $\Pi=(Gen,Enc,Dec)$ where $Gen$ take the security parameter $n$ as input and generates a key $k$ of length $n$. Generally speaking we say that $Gen$ ...
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PPT eavesdroper able to output $m_{0}$ and $m_{1}$ of different lengths

I've read the following two questions and their answers: Messages of different lengths and one-time computationally-secret Why is a non fixed-length encryption scheme worse than a fixed-length one? ...
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320 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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105 views

Biometric authentication [closed]

I see in some “Authentication schemes with biometric” papers that those authors wrote a phase as password and biometric update phase. My question is that why we may needs biometric update phase? Is ...
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568 views

How practical is proxy re-encryption for AES?

In proxy re-encryption schemes, a proxy is given special information that allows it to translate a ciphertext under one key into a ciphertext of the same message under a different key. How ...
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703 views

Elliptic Curve Encryption Ciphertext Size

I'd like to know how much bigger is the ciphertext when encrypting a message using ECC encrytpion? ECIES (or ElGamal)
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what is the state of the art algorithm to encrypt credit card data

We have a business requirement to keep credit card data. What is today's (Nov 2013) state of the art algorithm to encrypt credit card data that will be saved on disk? Additionally, I'd appreciate ...
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Learning to encrypt/encryption algorithms [closed]

I am a beginning programmer interested in coding an application of my own to encrypt sensitive files of mine. For example: lists of passwords, bank accounts, Credit Card numbers etc. I was wondering ...
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Is compressing data prior to encryption necessary to reduce plaintext redundancy?

As explained in William Stallings' Book, in PGP encryption is done after compression, since it reduces redundancy. I couldn't relate encryption strength with redundancy. Could anyone explain more on ...
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244 views

How to store keys for a cascading encryption?

What is the best way to implement a cascade encryption? I'm trying to figure out how to cipher a string (or message) using Serpent-Twofish-AES and then store the keys. I'll provide an explanation, ...
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331 views

Can two people with different one time pads securely exchange a message like this?

Alice has a message, generates a one time pad, encrypts her message and sends it to Bob. Bob generates his own one time pad, encrypts the message again, and sends it back to Alice. Alice then decrypts ...
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How can an encryption scheme be indistinguishable with multiple messages but vulnerable to an adaptive chosen-plaintext attack?

In order to be indistinguishable with respect to multiple messages, wouldn't the scheme need to be nondeterministic? How would this then possibly be vulnerable to an adaptive CPA?
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Why is $-1$ an illegal message in the Goldwasser-Micali Encryption Scheme

I'm not sure why in the Goldwasser-Micali encryption scheme with a Blum integer $N$, the message $-1$ is always a illegal message. Can you give me some direction for starting? What is illegal ...
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1answer
82 views

How to pass an arbitrary signature to a certificate

I am trying to sign certificate (X509) using secret sharing. That is shareholders combine their signatures to produce the final signature which will be in this case the signed certificate. However ...
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Is this hand cipher any more secure than the Vigenère cipher?

I know that inventing one's one crypto always sucks, but the problem is that hand ciphers are usually very insecure very slow. This is an attempt to make a relatively secure, keyable, and ...
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428 views

randomly generated key reused with XOR

If I have a long randomly generated key (k), XORed with a message (m), but since the message is longer than the key, there is a chance of reusing the keystream with the same message, but the key is ...
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112 views

Is there a developer's resource that ties encryption methods and strengths to the appropriate usage scenarios?

I'm not looking necessarily for implementations in any language (although it would help to list those resources as well), but what I am most interested in is a discussion of what advantages and ...
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plaintext and its encrypted version known [duplicate]

I have a (long) text in two versions, encrypted and plaintext. I think it was encrypted using a substitution cipher method (I'm pretty sure, indeed). I'm not good in this matter, I know little about ...
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Question about the definition of a perfect cipher

I need to prove that the following encryption scheme is a perfect cipher: Let $p$ be a prime. The secret key is a pair $(a,b)$ sampled uniformly at random from $\mathbb{Z}_p^* \times \mathbb{Z}_p$. ...
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Password as it relates to various encryption schemes

Suppose you have 2 drives you want to encrypt using different encryption algorithms, as an example: AES256 and Twofish. I am aware that using the same password for both could potentially weaken ...
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190 views

Public Key encryption /Assymetric encryption

For a start, I 've got a question regarding the Public key encryption. I know the public key encryption overcomes the Key distribution issue with the symmetric encryption and that in the case of ...
3
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1answer
521 views

How does the IV or initial counter increase internally for each block in AES CTR mode?

I am working on Intel AES-NI library and since the AES function is coded using low-level assembly instructions. I could not see how the IV or initial counter increases in CTR mode. In general, how ...
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Are there any simple and yet secure encryption algorithms?

Being very new to C++ and cryptography, I finally managed to implement a version of the Vinegere algorithm. I would like to try something a bit more complicated. I have looked at AES and DES and ...
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Why does Merkle's Puzzle requires Eve quadratic complexity of effort to break the system?

The way Applied cryptography 2ED explains the puzzle is as follows (I paraphrase it): Bob generates 2^20 messages of the form x,y where ...
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Are there attacks that break collision resistance but not preimage resistance?

Are there any examples of attacks on hash functions which: break collision resistance and second preimage resistant, or break collision resistance and preimage resistant? I have looked at Rogaway'...
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What's the difference between the long term key and the session keys?

I'm currently studying secret key cryptography, and I've come across the terms "long-term key" and "session key". What's the difference between these two kinds of keys?