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Questions tagged [compression]

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

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Protocol for verifying novel compression algorithm?

By the pigeonhole principle, we can demonstrate that arbitrary lengths of random data are uncompressible in the general case. But let us imagine that I claim that I have created an oracle that can ...
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Keystream reuse in AES-256 in AE-2 encrypted ZIPs

Is keystream reuse a meaningful concern in AES-256 encrypted ZIP files that adhere to the AE-2 spec? From “Attacking and Repairing the WinZip Encryption Scheme” by Tadayoshi Kohno when using 256-bit ...
Michal Charemza's user avatar
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WinZip AE-2 for small files and AE-1 for larger - how small/how large for each?

I'm adding password protection/encryption support to a Python package that makes ZIP files (https://github.com/uktrade/stream-zip). I'm opting to not add ZipCrypto support, but instead add WinZip-...
Michal Charemza's user avatar
2 votes
2 answers
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CRYSTALS-Kyber Compress and Decompress function role

I was reading CRYSTALS-Kyber design. They have used compress_q(x,d) to scale an element of $\mathbb{Z}_q$ to $[ 0,1,...,2^d-1 ]$. The definitions of ...
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How much can we compress RSA public keys with two equal size factors?

Can we define an RSA variant in which the public key with $n$-bit public modulus $N$ has a compact representation of $\kappa\ll n/2$ bits, with a security argument that it is as safe as regular RSA ...
fgrieu's user avatar
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Does compressed data expose information about non-compressed data when encrypted together?

I know that compressing data before encrypting it can cause a compression oracle attack such as in the CRIME and BREACH attacks, but if only part of the data is compressed, e.g. non-user controlled ...
Aaron's user avatar
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Technical feasibility of a theoritical compression mechanism

Considering that quantum computers (in theory) can break\reverse some of one-way-hashes a lot faster than conventional-computers. Is it technically feasible in any theoritical (but realistic) senarion,...
Giorgos Xou's user avatar
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Compression algorithm with multiple valid same-sized outputs

Is there a lossless compression algorithm that has hashing-like properties where there are multiple solutions to it? As in for example, when a 1000-bit data-sequence is compressed into a 500-bit data ...
Tensor's user avatar
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Shortest encryption with URL-friendly character set

I need a way to encode a set of information in a way that the result would be as short as possible with a requirement of it being usable as part of URL string. I don't really care that much about ...
mnj's user avatar
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SPKI Public Key to Compressed Public Key

I currently have a DER-encoded X.509 ECC SECP256K1 public key, also known as SubjectPublicKeyInfo (SPKI) from AWS KMS. How do I convert it to a 66 hexadecimal compressed public key string?
yijie's user avatar
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Would compressing encrypted data and compressing digital signatures be bad for security?

I understand that compressing encrypted data and compressing digital signatures are not efficient because they are most likely incompressible. But in my application encrypted data and digital ...
ANISH M 18CS006's user avatar
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In a PGP like Application , would compress and encrypt leak information

would compress and encrypt on data comromise security for PGP like application, would it be secure for use in Encrypted Messaging? I have heard its safe for data at rest encryption , i have heard ...
ANISH M 18CS006's user avatar
2 votes
2 answers
532 views

Compression and Decompression in CRYSTALS-Kyber

I am currently studying the Kyber Paper. I have a question about section 2.2 Compression and Decompression, but first I would like to quote the statement: Compression and Decompression. We now define ...
P_Gate's user avatar
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Compressed Address public key [closed]

Is it possible to get the x, y of the compressed public key? I have decompress it and naturally it gives the xy of the decompress public key. I need the xy coordinates of my compressed public key . ...
Roy Nahar's user avatar
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Is it safe to rule out compression and encryption if the payload has sequences of repeated bytes?

This question was originally asked on Reverse Engineering SE, but I felt that the main part of my question doesn't relate to RE directly, and it's more about a fundamental understanding of ...
Schro's user avatar
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Is the signature in PGP compressed as well, or just the contents of the message?

I am developing an implementation of OpenPGP, and I'm using Kleopatra to test my generated messages. After generating a signature for a message, I compress both the message and signature, but upon ...
S.Ptr's user avatar
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Get Pixel Data from JPG/JPEG but still bring the integrity? [closed]

As far as I know, JPG is a lossy image compression format Meanwhile, BMP is a generally uncompressed image format, whose file structure consists of bitmapFileHeader (14 bytes) and bitmapInfoHeader (40 ...
akez's user avatar
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Hashing functions that allow to walk back to parts of cleartext?

Say $m$ is some clear text, and $h_n(m)$ is its $n$ bits hash. The question: How can we design $h_n$ so that we can extract maximum information about $m$ from $h_n(m)$? The reason I ask this is ...
caveman's user avatar
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9 votes
3 answers
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Can one use a reversible hash algorithm as a compression function?

As we know any input to SHA-256 will be returned as 64 hex length output. Is it possible to create a hash that can do the same thing as SHA-256 but can be reversed, so if we have the output of 64 ...
Вања Хочак's user avatar
5 votes
3 answers
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Why is the output of a True Random Number Generator (TRNG) insecure after it has been compressed?

I came across the following statement regarding true random number generators (TRNG): A “P1 medium” [AIS31] true random number generator (TRNG) may not be directly used due to cryptographic reasons. ...
Jordan's user avatar
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Can I compress $192$ byte key into $16$ or $32$ bytes which can be later used in KDF to recover full key

I have a key $k$ which is $192$ bytes long. Is there a secure way to first compress this key into $16$ or $32$ bytes, but in such a way that later given those $16$ ($32$) bytes I can use a key ...
Ziva's user avatar
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2 votes
1 answer
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Can we calculate the "previous hash value" in the SHA256 compression function with a known message block and final hash?

Suppose we have a $512$-bit (or $512\times n$ bit) message that we'd like to hash using SHA-256. I've looked at the implementation, and from what I understand, after padding, there will be a total of $...
George T's user avatar
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Reducing a 64 digit integer to 10 digit

Situation:- I am using Python. I am using RSA and I am using two 64 bit keys. I am not an cryptographer . I can provide you the RSA code if needed but i am not posting it as it doesn't have to do ...
Ritvik's user avatar
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2 answers
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What is the difference between data compression and compression in cryptographic algorithms?

What is the differences between data compression as used in e.g. the ZIP protocol and compression as performed in cryptographic hashes? Are there common properties as well, apart from creating a ...
Maarten Bodewes's user avatar
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Using RSA encryption to encrypt large files

The following post discusses the use of RSA for file encryption: https://medium.com/@ismailakkila/black-hat-python-encrypt-and-decrypt-with-rsa-cryptography-bd6df84d65bc The file encrypted is a JPEG ...
learnerX's user avatar
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Entropy Preserving Functions

Let F be a deterministic compression function that takes fixed length 128 bit inputs and outputs 8 bits. Each input to the function has 128 bits of entropy, does that mean that the output byte has 128 ...
William Hird's user avatar
2 votes
1 answer
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Checksum for bailing early on first corrupt byte in stream?

Suppose you want to transmit bytes of a file from computer a to b, but you want to bail early if any of the bytes are wrong. It’s easy to prescribe a hash/checksum implementation for the entire file. ...
William's user avatar
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How reassuring is CRC-then-XTS as authenticated encryption?

It is known that the "xz" compression format embeds a checksum in the compressed file to verify integrity during decompression or standalone testing. The algorithm of the checksum can be one of: CRC32,...
DannyNiu's user avatar
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If an algorithm can not produce a true random stream, then an algorithm can not alter its entropy [closed]

Can a transform lower the Kolmogorov entropy of a true random stream and then restore that stream with out loss. If not true then this means a transform can not raise or lower the entropy.
Jon Hutton's user avatar
16 votes
6 answers
5k views

Is the decompression of compressed and encrypted data without decryption also theoretically impossible?

We have two communication points in an information system, call them A(lice) and B(ackup). B has to store encrypted data received from A. The storage of B is encrypted, but not compressed1. B should ...
peterh's user avatar
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Is it necessary to transmit two or three points of an elliptic curve?

Are there cryptographic protocols, where a party should transmit by communication channel simultaneously two or three $\mathbb{F}_q$-points of an elliptic curve over a finite field $\mathbb{F}_q$? ...
Dimitri Koshelev's user avatar
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6 answers
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Can a large file be hashed down to 32 bytes, and then reconstructed from the hash? [duplicate]

We can hash a file or data using multihash or SHA-256, but can we retrieve the original data or file from the hash? Are there any methods to retrieve the original file or data from a hash of it ...
Anu Davis's user avatar
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4 votes
2 answers
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AES-128 as compression function in Merkle-Damgard construction

Using a compression function $f : A × A → A$. A basic version given by: $W_0 = IV$ $W_1 = f(W_0, m_1)$ $W_2 = f(W_1, m_2)$ ... $W_n = f(W_{n-1}, m_n)$ $W_n$ is the output of the hash function, $...
Hughtwo's user avatar
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2 votes
1 answer
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Password protection in ARJ: 3 characters of password are retrievable

On this site there is information that one can know first 3 characters (bytes) of the password without brute force. I know that ARJ in older versions has very simple encryption, i.e. XOR with ...
Setplus's user avatar
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1 answer
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The collision rate probability decreases when using compression?

Some standard compression procedures, like the IANA's gzip provided by HTTP protocol, will consume CPU-time anyway... So we can reuse compressed file, $Z(x)$, in the checksum procedure. That is, we ...
Peter Krauss's user avatar
2 votes
1 answer
222 views

Are there any algorithms or alternatives to create short signatures?

I am searching for a algorithm to verify that a short message (size of about 20-30 bytes) was created by a specific device/user. The device/user can be partially offline. Signing the data using rsa ...
Florian's user avatar
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1 answer
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Why can an arbitrary compression function mapping $\{0,1\}^{m+2^m} \rightarrow \{0,1\}^m$ not seriously be considered collision resistant?

I recently got a question that I’ld like to share here, since answers might be useful (or at least interesting) for people diving into Merkle-Damgård hash constructions for the first time. We know ...
e-sushi's user avatar
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1 vote
1 answer
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Can compression + encryption sometimes be beneficial?

I hope this question hasn't been asked before: I searched and couldn't directly find it. It is known that in specific applications, compression followed by encryption leaks information of the length ...
entrop-x's user avatar
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3 votes
2 answers
387 views

Decrypting two XORed compressed messages?

If through a previous attack, cipher misuse or two time pad etc. I receive $c=m_1 \oplus m_2$. Where $m_1$ and $m_2$ are compressed messages, for instance GZIPped English text documents. Can we ...
Meir Maor's user avatar
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1 vote
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Is it possible to compress a random sequence with high entropy?

I have an algorithm that generates a pseudorandom sequence with a length of 100k and high entropy. I would like to check the quality of its randomness. So, I used a popular software program to ...
David's user avatar
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1 answer
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What are the differences between Encrypt+Compress and Compress+Encrypt a.When and where do we use them, explain it in a scenario

please help me with this What are the differences between Encrypt+Compress and Compress+Encrypt When and where do we use them, explain it in a scenario Thanks & regards Pavan
Pavan's user avatar
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2 votes
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Is TLS 1.2 compression methods in client_hello a mandatory field?

As stated int he question, is compression methods list in the client_hello in TLS 1.2 a mandatory field (it is clear that it is mandatory in session_resumption, but not clear to me whether it is ...
user6875880's user avatar
4 votes
2 answers
407 views

Can compressed data be made to look like random data?

I saw the question "Decryption honeypots" and realized that if the message was compressed before being encrypted, then checking compressibility would not help you identify the decoded message. So if ...
daniel's user avatar
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3 votes
0 answers
174 views

CRIME - attack TLS compression

In the CRIME attack slides at the Ekoparty presentation (where it was first introduced), I didn't get something. In slides 32-35 ( https://www.ekoparty.org/archive/2012/CRIME_ekoparty2012.pdf ) When ...
user avatar
-1 votes
1 answer
82 views

Integrity of Voice packets/ Audio signal

for encryption data packets, one should use GCM, CCM or EAX mode of operation to have confidentiality and integrity. What to do in case of voice packets? is it enough that audio signal gets compressed ...
crypt's user avatar
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Is it possible to recover password having ZIP/AES file and unpacked file?

Is it possible to recover password having ZIP/AES file and unpacked file? Or unpack other files with the same password?
flig's user avatar
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3 votes
1 answer
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How do you represent a compressed point on an elliptical curve over F2m?

I understand for prime curves it is just bytes(0x02 + flag) + bytes(x) where flag is the LSB of y. For the F2m curves I ...
Ofekmeister's user avatar
1 vote
1 answer
240 views

Ciphertext compression (Ring-LWE encryption and authentication system) after encryption?

Recently I came across an interesting looking cryptography article Ring-LWE Ciphertext Compression and Error Correction: Tools for Lightweight Post-Quantum Cryptography by Markku-Juhani O. Saarinen, ...
Veksi's user avatar
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1 vote
1 answer
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Is using Euler's Totient/phi in Tonelli-Shanks (used to recover EC coordinate) safe?

I'm implementing an algorithm in order to recover the $y$ co-ordinate from $x$ in order to construct a co-ordinate pair that satisfies secp256k1's elliptic curve equation, which is: $y^2 = x^3 + 7 \...
bekah's user avatar
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5 votes
2 answers
1k views

Will compression help defeat single letter frequency attack against a mono alphabetic substitution cipher?

Alice has a long message to send. She is using mono alphabetic substitution cipher. She thinks that if she compresses the message it may protect the text from single letter frequency attack by Eve. ...
JavaiMaster's user avatar