Compression is the reduction in size of data without losing information.

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1answer
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What is safer: ZipCrypto or AES-256?

Like in title: which one of these encryption methods (ZipCrypto, AES-256) is more secure and why? I am asking about it because I'd like to know which should be preferred when compressing files with ...
21
votes
2answers
1k views

Selective format-compliant JPEG encryption?

I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping ...
12
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4answers
2k views

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 ...
7
votes
2answers
2k views

How much can we compress RSA public keys?

I am wondering to what degree we can define an RSA variant, with a security argument that it is as safe as regular RSA with a given modulus size $m$ (e.g. $m=2048$), in which the public key has a ...
7
votes
1answer
186 views

How can ECDSA signatures be shortened (to be used as a product key)?

So I made my own serial key generation software, using ECDSA, for use in my own applications and it works great so far! To keep the serial key short enough I use a 128 bit EC curve. My final signature ...
6
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2answers
2k views

Why is ciphertext from low entropy plaintext not compressible?

This comes following a discussion with a colleague. My plaintext file plain consists of a about 100,000 lines of "all work and no play...". It's size is: 2.2 MB. ...
6
votes
2answers
133 views

Is there a way to compress multiple signatures of the same data?

So, I'm working with a system that allows individual users to each have their own private-public key pair. I would like to allow multiple users to use their private key to sign the same piece of ...
6
votes
1answer
112 views

Performing simple arithmetic operations on compressed, and both compressed and encrypted data

We all know it is possible to perform addition and multiplication operations on encrypted data by means of homomorphic encryption methods. My questions are: Is there any cryptosystem that is able to ...
5
votes
5answers
2k views

Crypto-Compression Algorithms?

I was wondering, whether there exist such algorithms/enciphering procedures which both compress and encrypt the input data. That means, for starters, the output will be both smaller in size and ...
5
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5answers
232 views

Is it better to encrypt before compression or vice versa?

Is it better to encrypt a plain text file before compression, or vice versa?
4
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1answer
167 views

Compression function to guarantee randomness of one time pads?

First of all, I would like to note that I am not building my own crypto. I am simply curious and would like to learn. What I am wondering is this: if we are worried about randomness of something ...
4
votes
1answer
112 views

OTT service using FPE

Would it be possible to create an Over-The-Top communication utility that will encrypt voice using format preserving encryption (voice clear-text to audio encrypted stream) and send that over an ...
4
votes
1answer
130 views

Is it ever unsafe to compress an EC point?

I am working with a library that outputs EC points in uncompressed form. To save space, I'm considering modifying said library to use compressed EC points. Assuming that I keep track of the sign bit ...
4
votes
1answer
212 views

Repeatable crypto

Is there a safe way to do crypto that will always produce the same result for a given input? My use case is transferring deltas of huge files, to a backup server. The backup server has no knowledge ...
4
votes
1answer
285 views

How secure is this use of Ziv-Lempel encoding?

I'm reading patent application US 20120278897 A1 — “System and method of sort-order preserving tokenization”. Near the bottom they describe their token generation algorithm, which basically involves ...
2
votes
4answers
2k views

Is there an existing cryptography algorithm / method that both encrypts AND compresses text?

So I'm trying to find a method of encryption that not only obfuscates text, but also compresses the result. For example, if I encrypted ninechars, the ideal result ...
2
votes
2answers
485 views

How does compression before encryption leak info about the input?

Apparently current best practices recommend that you do not compress before you encrypt. For example in this blog entry (*): http://sockpuppet.org/blog/2013/07/22/applied-practical-cryptography/ It ...
2
votes
1answer
322 views

Using compression to test encryption

Is the uncompressibility of encrypted data a necessary property for a good cryptographic algorithm? To make a crude experiment, I encrypted an 8K file with all 'A' and then compressed both the ...
2
votes
2answers
290 views

Seeking special-use fingerprinting/hashing algorithm

For a project I wonder if there exists some kind of fixed-size checksumming/fingerprinting function in which based on this fingerprint given data block 1, it is easy to generate more data blocks that ...
2
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2answers
1k views

Does it make sense to have a compression function that uses 64-bit of the message to create an output of 64-bit?

I have a very simple compression function, which looks like this in C++: ...
2
votes
1answer
61 views

Compression in Symmetric-Encryption?

When using symmetric encryption is it important to compress the data first? I think that compression will make data look "more random" and this might help the ciphertext be harder to crack but I am ...
2
votes
1answer
235 views

Extracting a WinRAR password

If I have an original file and a WinRAR password protected .rar file containing that file, than can I extract the password?
2
votes
1answer
487 views

Is it safe to use GZIP to avoid padding related attacks

I am designing a library that supports encrypting some in-memory data using AES in CBC mode. Now I need a padding but it seemed to me that Apple's CommonCrypto library and OpenSSL have different ...
2
votes
2answers
1k views

Attack XOR encryption of binary data compressed by zlib with known key length (very short key)

I am trying to break a packet format. The packet format simply packs several files into one big file. The file contents are plain. But the index data which contain offsets, file sizes and filenames ...
2
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1answer
80 views

Compression in key generation of DES algorithm

Does anyone have a pseudo-code or an algorithm or even a diagram of the compression (pc2) of the DES algorithm? I can't find a relation between the bits that are dropped, even when I do it manually ...
1
vote
3answers
348 views

Why can't we use a hash with no collision to compress data reliably?

According to wikipedia, a hash maps digital data of arbitrary size to digital data of fixed size. For all practical measures, a hash is a unique signature of a big chunk of data. But there is such a ...
1
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3answers
438 views

Point decompression on an elliptic curve

I'm programming an elliptic curve cryptosystem and I'm having difficulty with decompressing points. The following information is from my project specification as to my understanding: Given a point $x$...
1
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1answer
20 views

Can a compressed checksum be considered unique

I'm kind of guessing that the answer may be no. Since the compression is trying to reduce the output size using various optimization methods, this may cancel the properties of a hash algorithm. But ...
1
vote
1answer
250 views

SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)

The hashing scheme SHA-256 (for instance) is based on Merkle-Damgard construction with the underlying compression function based on the block cipher SHACAL-2 configured in Davies Meyer mode. SHACAL-2 ...
1
vote
1answer
56 views

How does the attacker include input before compression and encryption in CRIME?

I have read this article about the CRIME attack against TLS and SPDY. The article says that: What is not yet clear is how the attacker is including their input in the source material before it ...
1
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0answers
54 views

Is it possible to enumerate the possible RSA keys? [duplicate]

As far as I understand ECDSA keys are smaller than RSA because all of the value of the ECDSA (up to a high number) are valid private keys. Is there any method of compressing RSA keys, based on some ...
1
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0answers
40 views

Compressing AES [duplicate]

I have this program which encrypts multiple files using AES then compress it using LZO into one single file. The problem is that the final file is almost equal in size than all the files which means ...
1
vote
1answer
95 views

Decryption of Huffman code

I know that Huffman is not a encryption method, but I have a bit-stream that I know it's Huffman coded. However, the tree/table that maps the codes to real characters is not available. Surprisingly, ...
1
vote
1answer
107 views

If classical ciphers are used with compressed plaintext, how much does it make frequency analysis attack harder?

Classical ciphers, such as Vigenère cipher, are weak and no longer be used. They can be broken by using frequency analysis, that is a well-known fact. But, the frequency analysis often depends on the ...
0
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2answers
61 views

Would a non-deterministic (read: randomized) compression algorithm be crypto-safe?

Would a compression algorithm that randomly shifts stuff around every iteration be TLS/crypto-safe? This randomization would prevent the same byte sequence from appearing twice in a row, thus making ...
0
votes
1answer
118 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 ...
0
votes
1answer
27 views

How to compare two CSPRNGs? [duplicate]

Let's say I am given to CSPRNGs: RNG1 and RNG2. I want to select the best one of the two for cryptography. How should I do it? Any of the two RNGs can be initialized with a secret key during tests and ...
0
votes
1answer
121 views

Huffman encoding of hashes

I have a huge list of MD5 hashes, which takes up quite some space. I was wondering if I would acheive (some) compression, by encoding the characters (which are A-F 0-9), with huffman coding. I made a ...
0
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0answers
52 views

Symmetric encryption with compression for MySQL DB data

I would like to compress data before encrypting and storing it in a MySQL DB to reduce especially bandwith requirements (compression reduces bandwith by 70-80%). At present, all is handled by a server-...
-1
votes
1answer
263 views

data structure of random / compressed data

can anybody explain to me what data structure results after data is compressed? I just try to find out the difference between random data and compressed data, the entropy of both is very high while ...
-1
votes
1answer
94 views

Keccak and compression functions

Keccak follows a sponge construction. Can we say that Keccak employs a compression function? Generally speaking, for sponge constructions, can we say that there is an underlying compression function?
-1
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0answers
26 views

Identify a hash which was already seen? [closed]

I have a question. In our group we are processing a large number of datasets. Each one is identified by its hash (pseudo-random ASCII string). We are currently looking for a way to tell if we already ...