Encryption is the process of transforming plaintext using a cipher to make it unreadable to anyone except those possessing the key.
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Practical necessity of semantic security under chosen plain text attack (CPA) in CBC mode
I was not able to understand why we practically need a CPA security in Cipher Block Chaining. (which insist on having a random IV), let say if the encryption is not CPA secure i.e , the adversary can ...
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Avalanche effect in DES
I couldn't understand the avalanche effect in DES. Could someone explain how avalanche effect happens in DES
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1k views
How do I correctly derive a Key and IV?
Mainly I'm trying to understand how to correctly create the Key and IV for use with the .NET Implementation of AES (AesManaged class).
This encryption code will be used in conjunction with existing ...
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256 views
If the PSK is known, is it possible to decrypt traffic from other clients in a WPA2 wlan network?
If in a public WLAN WPA2-PSK is used, but the PSK is more or less publicly available, does this mean that an attacker with that PSK can easily decrypt wlan traffic from/to other clients of that WLAN?
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Creating an encryption key from several other keys and using hash functions
I want to combine two or more keys to create a single encryption key that relies on all of them. What is the proper method for doing that? Simple XOR? Using hash functions? Something else?
I ...
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846 views
Why do we need special key-wrap algorithms?
Wikipedia says:
Key Wrap constructions are a class of symmetric encryption algorithms designed to
encapsulate (encrypt) cryptographic key material.
We are using these algorithms to encrypt ...
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142 views
How are state wiretaps obtaining plaintext from encrypted transmissions?
According to the US 2011 Wiretap Report, encryption — on the off chance that it is encountered — has been no hurdle to retrieving the content of a conversation.
Public Law 106-197 amended 18 ...
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Security of tokenization of plain text conversations - cryptanalysis
I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
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110 views
How to turn adversary against encryption of zeroes into adversary against random bits?
I recently read the article Nonce-Based Symmetric Encryption by Rogaway, where he presents two different notions of indistinguishability, which he calls ind$ and ind, respectively. Here's the ...
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Encryption algorithm that produces dummy output on incorrect passwords
Background:
I've been thinking about using encryption in the context of backing up files to untrusted locations (to the point of making the file publicly and widely distributed for practically ...
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335 views
How to break an arbitrary XOR and Rotation based encryption?
I heard encryption based purely on XOR and Rotation is inherently weak. The paper Rotational Cryptanalysis of ARX says:
It is also easy to prove that omitting addition or rotation is devastating, ...
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What's the fundamental difference between Diffie-Hellman and RSA?
What is the difference in the purpose of DH and RSA? Aren't they both public-key encryption?
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K out of N encryption
A friend just showed me how to combine padlocks to achieve a lock that opens when k out of n people turn their keys.
I was ...
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153 views
How can I store confident data with OpenID?
I want to make a system that needs to store some confident user information in a database. I intend on using OpenID for user authentication.
I would like encrypt the data in a way that it can only be ...
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624 views
GPG symmetric encryption and javascript
I have a use case where I need to encrypt some text in the browser using javascript. Only the encrypted text will be stored on the server.
The user should then be able to take the encrypted result ...
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97 views
Using encryption schemes for identification
I've been researching how to implement a post-quantum SSL-like connection authentication, especially correct identification&authentization of the server/client. Because good post-quantum digital ...
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192 views
Are there any Implementations of Secure Indexes?
There are several papers about Secure Indexes, for Example "Searchable Symmetric Encryption:
Improved Definitions and Efficient Constructions" and "Secure Indexes". ...
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315 views
How and why can a decryption program tell me that a key is incorrect?
I have noticed that some programs used for file encryption will tell you if an entered key is wrong when you try to decrypt. It seems (to me at least) that this would mean that the key somehow is ...
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Using CBC with a fixed IV and a random first plaintext block
What if, instead of using CBC mode in the normal way with a random IV, I used this approach:
Use a fixed IV (like a block of 0's).
Before encrypting, generate a random block and prepend it to the ...
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542 views
Is it feasible to build a stream cipher from a cryptographic hash function?
A few years ago I devised a symmetric-key system that worked like so:
...
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Is there a way to make RC4 (ARCFOUR) secure, or is it completely broken?
I need a method to authenticate a process with another in order to establish interprocess communication between them, to prevent malicious processes from trying to hook onto the system. Currently I ...
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Why programming languages don't provide simple encryption methods?
In c#, there is a namespace called System.Security.Cryptography and there are many classes in this namespace, which help developers encrypt and decrypt data. ...
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253 views
After implementing a novel encryption algorithm, how would one go about analyzing its security or get help from others in doing so?
Preface: This question was originally asked on Theoretical Computer Science and later on Computer Science. The kind people on cstheory.SE referred me to this web site. It is being repeated here in an ...
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How can one securely generate an asymmetric key pair from a short passphrase?
Background info:
I am planning on making a filehost with which one can encrypt and upload files. To protect the data against any form of hacking, I'd like not to know the encryption key ($K$) used for ...
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761 views
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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193 views
What other one-way functions are used in cryptosystems?
For RSA and El Gamal (and most other public key cryptosystems), one of the key ideas is that factoring and finding discrete logarithms are hard. There are other systems that rely on certain properties ...
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Encryption with “constant” initialization vector considered harmful
I try to get the full reasoning behind the above statement. First, after reading articles here and at wikipedia i understand that using an IV only once is good practice.
For stream ciphers not doing ...
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147 views
Can I jettison MAC if I already have SHA1(M)?
I'm currently using SSL with AES-CBC and HMAC for a file transfer containing string M. Now suppose Alice already knows SHA1(M) (and the adversary does not), and she downloads M from Bob using only ...
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SIM security for two messages
Here SIM means the simulation based security
Consider a two message encryption scheme:$$Enc:K \times M \times M \rightarrow C \times C$$
and $Enc(K, m, m')=(K \oplus m, K \oplus m')$,
In ...
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What are the details of the DES weakness of reusing the same IV in CBC mode with the same key?
I think I once faced the recommendation, that the initialization vector should always be random and never be used twice with the same key.
How serious is this weakness?
Also, is AES less effected ...
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143 views
What is a block cipher?
I have read about block ciphers, but I do not understand the topic completely.
Is a block cipher a way to send data or a way to encrypt data?
How is the data divided into multiply blocks before it ...
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Is it possible to break a hash-based block cipher?
Let's define the following block cipher:
$C_n = M_n \oplus H(k + n)$ where $C_n$ is the nth block of ciphertext, $M_n$ is the nth block of plaintext, $H$ is a cryptographic hash function, and $k$ is ...
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126 views
Will varying plaintext compensate for a fixed initialisation vector?
This is a follow-up question to Relative merits of AES ECB and CBC modes for securing data at rest.
I need to store encrypted Personal Account Numbers (PANs) in a database. The only encryption option ...
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309 views
Are there two-way encryption algorithms that include a work factor?
I recently learned about the hashing algorithm bcrypt, which allows you to specify a "work factor" for the hash which can be incremented to stay ahead of Moore's Law. I understand there are some other ...
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141 views
In RSA encryption, does the value of e need to be random?
I am a novice programmer and am just finishing up an RSA encryption program that I am writing for practice. Currently I have the program generate a relatively small random value for the public key e. ...
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What is the appropriate public key encryption for secure coin flipping?
I quote Bobby's question here since I encountered the same one...
Random Coin Flip using ElGamal and a Trusted Party
Consider the following protocol for two parties to flip a fair coin.
Trusted ...
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Is Blowfish strong enough for VPN encryption?
I'm looking at an OpenVPN connection between two sites configured to use 128 bit Blowfish in CBC mode, and trying to figure out how to assess the strength, but I just don't know enough of the maths.
...
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101 views
What is 'security margin'?
I have been academic papers about Rijndael, Serpent, and Twofish, and there is this term that is vague to me. I cannot find a tangible definition in google. Can someone briefly define, describe, ...
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Can I use PBKDF2 for authentication and decryption?
I want to store a hash for authenticating a password. I also want to use the same password for decryption. Can I use PBKDF2 for both? (I plan to use different salts for the authentication and the ...
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404 views
How do I solve this RSA instance for m?
How we can solve this equation and get the value of M?
$$8 = M^{13} \mod 33$$
not a computer program, but a mathematical operation.
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What is the purpose of four different secrets shared by client and server in SSL/TLS?
I was looking through the working of SSL V3, and found that a connection state is defined by a set of things, including
client write mac secret,
server write mac secret,
server write key,
client ...
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79 views
Two way encryption with random IV
I'm attempting to encrypt some information into our database to be later pulled back out and displayed to the user. Searching and reading up on different methods I found a post over at stack exchanged ...
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328 views
Why is CBC with predictable IV considered insecure against CPA
I just learned that using CBC encryption with an IV which is predictable is not secure.
From what I understand, using certain plain texts, and then guessing the IV that is uses, the attacker can ...
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355 views
Order Preserving Encryption for Numeric Data Values
How can I ensure order of encrypted data i.e., Enc(m1) < Enc(m2) where m1 < m2, and all messages are integer values.
I have gone through Order Preserving ...
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Why does RSA give better security on longer messages?
I am trying to understand the notion of RSA security.
Choosing a public exponent where $e = 3$ facilitates the calculations, considering that it is secure if the plaintext or message is long.
If the ...
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200 views
Provable Encryption
Is it possible to encrypt data in a way that it can be proven that the data is encrypted, without revealing the key?
Alice chooses some plaintext, then she encrypts it with a certain scheme. She ...
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1answer
190 views
repeating-key xor and hamming distance
I read that to break repeating-key xor you can do the following: try a keysize $n$ and compute the hamming distance between the first $n$ bits of the encrypted string and the bits $n+1$ to $2n$ of the ...
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Future-Proof Versioning and Validation
I am working on a library (using standard primitives: AES256 CTR; HMAC with SHA256; PBKDF2 with SHA256, 128 bit salt, and 10000 rounds) to encrypt and decrypt data, given a password.
The encrypted ...
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Dimension of Encryption of a linearly dependent set of plaintexts
Suppose I have an encryption scheme of the form $ E(P)=C $ where $P$ is the plaintext and belongs in $\{0,1\}^N$, $C$ the ciphertext which belongs to $\{0,1\}^M$ and the encryption is performed under ...
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Is the encryption of a hash a good MAC?
At university we were told that it is a bad idea to implement a MAC by simply concatenating a key with the data to sign and to run it through a hash function (e.g. $s = ...
