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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What are the vulnerabilities of this homemade encryption algorithm? [closed]

I decided to program a relatively trivial encryption algorithm in my downtime. This algorithm takes a seed from a user (supports floating point seeds), and then adds 1 to the seed for every iteration ...
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Is it possible to match encrypted documents using user-defined search terms?

Suppose I am storing a number of encrypted documents in a database. I would like to make it possible to identify the subset of documents whose contents match user-specified search terms without a) ...
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How can mega store my login details and still be secure?

I understand how Mega's encryption works. For a quick summary of all those in the future looking for an answer on this... here is how it works: Upon first signing up for an account you make a ...
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Why does the recommended key size between symmetric and asymmetric encryption differ greatly?

In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
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1answer
271 views

Cryptography system by combining a block cipher and a stream cipher

I have to come up with a design for a cryptography system by combining a block cipher and a stream cipher. I can't seem to come up with anything on my own. Can someone point me in the right direction ...
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1answer
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Stacked LFSR - why not used?

New to cryptographic, weak in math. I have designed a PRG which consist of 33 LFSR's, each 32 bits wide. I use one of the LFSR's as "selector", using the 5 LSB from this register to select one of ...
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1answer
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Practical brute-force attack on 128 bit encryption

In brute-force attack calculations cryptographers say we should assume an attacker will find the key after $2^{(n/2)}$ tries. If n=128, then n/2=64. We know that this is practical (A 64 bit key is ...
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1answer
83 views

Difference between the TLS cipher suites?

TLS_DHE_DSS_AES256_CBC_MAC / TLS_DHE_RSA_AES256_CBC_MAC Hi, I have been studying to learn about various cipher suites and their performances. I gathered that DSS is efficient when compared with RSA. ...
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1answer
180 views

Key sizes supported by 3DES

I read about 3DES encryption but I don't understand exactly what the specific meaning of key size is. For example I found that 3DES supports 64, 128, 192, and 256 bits key size. What are all the ...
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common ways / methods to try to break a SP network

I have a very little cryptography background (but a relatively solid maths background) so my below question is very general. Basically I have been given a SP network with an output to reverse. I ...
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1answer
104 views

NTRU Encryption

It's using Euclidian inverse. Can you show it step by step? $$N=7, q=11, a = 3+2X^2 -3X^4 +X^6$$ the inverse of $a \pmod {11}$ is $$A=-2+4X+2X^2 +4X^3 -4X^4 +2X^5 -2X^6$$ How do we compute $A$?
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1answer
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Are modes of operation algorithms practical?

I took a cryptography class back in college, and now that I am working my 1st career one of the things currently on my plate is coming up with an algorithm to encrypt data before it's placed on the ...
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1answer
563 views

Is it safe to use PBEWithMD5AndDES?

I'm encrypting some of my (not so much important) files with PBEWithMD5AndDES. Is it a strong method or it can be de-crypt easily without knowing my selected ...
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1answer
57 views

Is it safe to encrypt data by simply randomizing chunks based on a permutation?

Say I want to encrypt the following text: "Today is March the 22nd, 2015". And say want to encrypt 8-byte blocks of data using the following permutation [6,3,0,1,5,7,2,4] to swap characters at those ...
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1answer
101 views

Why would using a random seed with other variables be bad for ecrypting if you can't guess the key?

I asked this on stack exchange with it being code based, but someone suggested to ask here. Basically, I've done a script in python and wanted an option to encrypt the input, but I couldn't get any ...
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1answer
80 views

How are RSA and ElGamal compatible in PGP?

I'm starting to play with PGP and I don't understand how if your key pair is RSA you can encrypt a message for someone whose key is for example ElGamal. How does the asymmetric key exchange work if ...
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1answer
97 views

How do you implement a cipher as one lookup table?

I am reading up on whitebox cryptography and have trouble understanding how are ciphers implemented as one lookup table? assuming my plaintext is just 4 bits so the size of my lookup table should be ...
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1answer
72 views

Is it safe to prefix the a key with a known value?

Almost every encryption algorithm is based on a secret key. I wonder when the algorithm is considered safe, does that also imply that I can prefix (or suffix) the key with a known value, as long as ...
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1answer
45 views

Creating a new cipher! [closed]

http://flashbackcipher.blogspot.ae/2015/03/introducing-flashback.html Hey guys the above is the blog for a new cipher, if you guys can take a look and suggest problems.. it would be of great help!! ...
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1answer
231 views

What is the most light-weight symmetric cipher thats still usefull?

I need a very light encryption scheme which costs almost no performance during encryption (while decryption may be slow). I found 5 algorithms: RC4, DES, LED, PRESENT, and Piccolo. But how do I ...
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1answer
99 views

MAC in SSH packet encryption, benefits to not including it?

What are the benefits to not including MAC in a SSH packet encryption? I understand what the MAC is there for, but if it was not included would there be an advantage? Is the MAC somewhat redundant ...
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3answers
85 views

Deciphering text encrypted with a changing cipher

I know there are many ways to crack basic ciphers were each letter is mapped to some other letter, but what ways are there to decode something that was encrypted using a cipher that changed after ...
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1answer
121 views

ECDSA for encryption

ECDSA keys are much shorter than RSA keys, but typically only used for signing, not encryption. Is there an accepted way of doing this? (https://bitcointalk.org/index.php?topic=196378.0 ...
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Composition of non-perfect encryption keys

Definition 1: A key $k$ is called perfect if it is uniformly distributed from the adversary's point of view; a key $k$ is called $ε$-perfect, if its distribution has an $ε$ trace (statistical) ...
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How would one crack a weak but unknown encryption protocol?

I asked a question on security.stackexchange, but was told it would be a better fit here: http://security.stackexchange.com/questions/32779/how-would-one-crack-a-weak-but-unknown-encryption-protocol ...
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1answer
97 views

Why not send the identity in the encrypted message?

I've recently started reading the book "Applied Cryptography" written by Bruce Schneier. Quite a few times I stumbled across protocols who send the identity outside of the encrypted message (see step ...
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86 views

why do files downloaded with http and https have the same size?

while working with Encryption mostly cipher text is always larger the plain text, why isn't that the case when downloading a file using https ? even that compression isn't much used anymore because if ...
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Requested to encrypt data with AES256, digital certification, timestamped

at my job we have been tasked by gov to encrypt some data we send to them. The "law" says we have to do the title above, but they only need us to do the AES256 thing because the data is not really ...
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1answer
60 views

RSA Decryption from samples

I am working on a project for a client which involves decryption of data which was encrypted using RSA. The system in question retains three independent copies of each data-set, but each copy is ...
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2answers
125 views

Why does consecutive permutations or consecutive substitutions not enhance security?

My professor stated that permutations which are done repeatedly does not further enhance security than just one permutation. He also stated that fact this applies to consecutive substitutions as well. ...
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1answer
97 views

How do you break encryption on a message? [closed]

This may seem like a simple question, but I have just started studying cryptography and I can't seem to find any information on this at all. I am trying to write a "simple" encrypted messenger using ...
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3answers
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AES encryption takes more time to decrypt than encrypt

I am trying to find how much time an AES encryption and decryption takes for a given amount of data and key. In all the cases encryption takes way lesser processing time than decryption. I tried to ...
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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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59 views

If the text was compressed before using traditional cryptography, how much difficulty increases for frequency analysis attack?

Traditional encryption is weak and no longer be used. They can be easily broken by using frequency analysis is a well-known fact. But, the frequency analysis often depends on the number of captured ...
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1answer
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Block cipher mode with diffusion on ciphertext

As I understand, diffusion property in AES-CBC ensures that one-bit change in plaintext will yield changes in all following blocks in ciphertext upon encryption. I'm looking for algorithm that will ...
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3answers
210 views

When is a cipher considered broken?

We've all read how some people claim AES is broken because there was supposedly a way to get the plain text from a cipher text faster than brute-force. But is this the definition? Is a cipher broken ...
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1answer
124 views

Repair AES-128 decrypted file

I decrypted a file which was encrypted with OpenSSL and AES-128 with the wrong password. Before I noticed it was the wrong password I removed the original file. Is there a possibility to reproduce the ...
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Encrypt-then-MAC: Do I need to authenticate the IV?

In the setting of Encrypt-then-MAC, do I need to include the IV in what I'm HMACing, or is authenticating just the AES-encrypted data sufficient?
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Remove padding (CBC) from decrypted text [closed]

I have a bit problem with padding. Everything goes fine when I encrypt the text BUT when I decrypt I see some extra characters. Sometime's one character sometimes more and I dont know how to remove ...
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1answer
51 views

What is the probability of finding 4 equal bytes? [closed]

Is it $2^{-32}$ or $2^{-24}$ as one byte is assumed to take a given value and the remaining 3 bytes should have the same value?
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Encryption scheme that allows compare ciphertexts based on the clear text [duplicate]

I would like to compare ciphertext based on the order assumed on the message space. So, do you know if there exists some encryption scheme with the follow property: Let $c_0 = E(m_0)$ and $c_1 = ...
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51 views

Key length requirement in a simple XOR implementation

I don't have much previous experience at all with cryptography, this is pretty much the first time I've tried anything similar. I'm trying to implement an extremely simple XOR encryption system in ...
2
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1answer
58 views

Can IGE mode be parallelized?

As far as I know, in IGE mode (infinite garble extension) each block depends on the previous one. In that case, can the encryption be parallelized? Is there some way to do it?
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Transport SA bundled inside a tunnel with encryption applied before authentication?

For IPsec I am considering different formats of ESP encryption and authentication. I am not sure what happens with "Transport SA bundled inside a tunnel with encryption applied before ...
0
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1answer
85 views

Encryption of numeric value using playfair

I am studying in CSE and in my recent exam paper, A question was asked as: Construct a playfair cipher for Plaintext: semester5 and key:technology. Generally as we are taught yet, there is no ...
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1answer
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FEAL-4 Fk Function 4 Rounds

As I understood in FEAL-4 it needs 4 pair of round keys. Which means that we need to launch Fk function 4 times. My problem occurs starting the 2nd round. At the first round we have the original 64 ...
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Looking for an adjustable compute bound decryption function

I'm looking for a way to decrypt data, but make it require varying amounts of CPU power to do so. Maybe this could be illustrated as e(m) = m' and ...
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1answer
125 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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2answers
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Multiple encryption of part of block

Is there any security risk in encrypting parts of blocks twice? I'd like to get around block sizes and make encrypted messages just as long as the unencrypted ones: Block 1: Byte 0 - 7 Block 2: Byte ...
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1answer
109 views

Drawback of ElGamal encryption

I am trying to find out some disadvantages of ElGamal cryptography but I'm not able to figure out what's wrong with the algorithm. The only one I found is that a known-plain text attack is possible in ...