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# Questions tagged [crc]

The Cyclic Redundancy Check is a non-cryptographic error-detecting code. While CRCs occasionally appear as parts of a cryptosystem, questions purely about CRCs and other non-cryptographic checksums are off-topic here, and should be asked on Stack Overflow instead.

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### Is it possible to calculate key(0) and key(1) of ZipCrypto using key(2)?

Here is Zipcrypto decryption algorithm: ...
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### How many bits of encryption are enforced in WEP (wired equivalent protocol)

I'm currently taking a computer security module in University and as part of a problem have been asked: My thought for the question is that no it does not provide 64 bits of security strength. This ...
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### Replace checksum with asymetric hash

The purpose is for a server to ensure the content of the flash memory of a slave IoT contains a good known firmware. The server does not have a copy of the IoT firmware code - but only a hash or ...
1k views

### How can I reverse a so-called CRC16 from the data?

I am trying to understand a request I reverse engineered which is sent to a Daly BMS over BLE. Those requests change the 'sleep after' in seconds of the BMS: For DDDD seconds: ...
2k views

### How to prove that CRC (with an initial value of zero) is linear?

I understand that, as stated here, CRC is not linear (with respect to XOR operator) in general, because it could be initialized with a non-zero value. I was wondering how to prove linearity, when zero ...
228 views

### Forming a 64 bit CRC from a 32 bit CRC

Suppose I have a 32 bit CRC function $\text{crc32}(x)$ that satisfies all the properties of a CRC. Suppose also that I am a lazy developer who wants to create a 64 bit CRC function but doesn't want to ...
200 views

### Why do the first two digits of the hash table not collide within CRC32?

In this Python CRC32 table look-up method, the polynomial is 0x104c11db7. I can understand that the generated table does not collide. After all, as long as the ...
113 views

### Error Check in Lattice PQC

I am by no means an expert in the PQC field and am just trying to self teach myself about it. I was hoping to look into error correcting in lattice. I want learn about error or fault detection as it ...
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### Is CRC32C (any) better than CRC32(B)?

Is CRC32C (any) better than CRC32(B)? I read that CRC32C (alias Castagnoli) is better than CRC32 (sometimes referred as CRC32B) in detecting errors but what that exactly means and how to check it ...
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### 16 bit (2 byte) Digital Signature

I'm developing an experimental Amateur Radio digital protocol for over-the-air data exchange. A part of any protocol over fallible transport layers is of course some kind of error control (ECC, FEC, ...
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### Does the authentification in GCM serve the same purpose as CRC32?

The purpose of the authentification is to ensure the data integrity. Let's just focus on the authentification part of the GCM which is using the Galois field multiplication to create an ...
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### How to properly cypher 16 bytes message containing a CRC checksum?

This question arose from a new context under early developments. If cryptographic operations are not well chosen or badly sequenced, please do notice it along your answer or comments: I am a layman in ...
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1 vote
461 views

### SHA-3 for Integrity

We used to use CRCs to check the integrity of files. For safety analysis we could associate a probability for detecting a corrupted bit in a large file. Now we are using an RSA Signed SHA-3 hash for ...
1 vote
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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,...
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### CRC32 catches errors, but then what's the point of SHA?

If crc or CRC32 is specially designed to catch errors, then what's the point of SHA or md4-5 or any other hashing function? What I did was, I had a 190 mb png file (rendered in 16k resolution with ...
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### Is it feasible to get a hash collision for CRC32, MD-5 and SHA-1 on one file?

I'm aware that individually, each has its weaknesses (especially CRC32), but is it feasible that a file could be created to falsely match all three?
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### Are LRC (Longitudinal Redundancy Check) or CRC (Cyclic Redundancy Check) of any use in modern day computing?

I am currently learning about the history of Data integrity / Error detection. In the old days of tape drives, LRC was used for error detection. They were also used (at certain point in time) for ...
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### CRC-16-IBM, Reversed 0xA001, Little Endian (DCBA) Implementation [closed]

Background I need to implement this algorithm in Node.js, but after searching everywhere I can't find an implementation. Code My first approach was reviewed by a member of StackOverflow and was ...
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### What is a fast good-uniformity hash function that if it's seed and it's hash values are unknown, can be strong as cryptographic hash functions?

The hash function is for an application that the input to the hash function is from a user's, hence the user can control the collisions, but the question is that if the collisions, the hash function's ...
2k views

### Can keyed CRC be used as a MAC?

Consider a "MAC" that uses a symmetric key $K$ to generate an authentication tag $t$ for a message $M$ in the following way: Concatenate a timestamp with the message (to prevent replay attacks)  m =...
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### RC4: Find the complete plain text of a ciphertext when we know part of the plaintext

I need to decrypt an encrypted file with RC4 to answer to a Internet challenge. The file in question is a dump of a Teensy ROM and it is completely encrypted. Luckily, it looks like it's a standard ...
1 vote
1k views

### Is CRC32 birthday attack independent of input?

I have a configuration table which stores all device of a system and the corresponding serial numbers : ...
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### Is triple-CRC-32 a bad (or not) idea for generating a uniform distribution hash? [closed]

I have an input of 288 bits (comprising 4 × 32-bit and 10 × 16-bit integers). I need to hash this to 96 bits with as few collisions as possible. I'm aware that CRC is a bijective hash, thus ensuring ...
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### Is it possible to make two files with the same size and the same MD5 and CRC32?

I have seen a lot of different files with the same MD5s. For CRC32 is quite easy to find collision. But is is it possible to make size, and two different hashes the same? I have seen many linux ...
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### How to truncate MAC to 32 bit?

I want to use MAC as an additional protection of UDP-server from DoS attacks. I prefer to keep MAC as short as possible and I assume 32 bit is good enough for this purpose. I'm going to make it based ...
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### Hash functions and polynomial division

I understand that a CRC verifies data integrity by producing a checksum, which is the result of polynomial long division. I've heard hash values referred to as hash checksums, so my question is ...
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### Tiny Firmware Authentication

I am developing a product based on the NXP LPC11C24 microcontroller. It will communicate with PC software to perform its work. I am attempting to build a secure firmware update functionality. The PC ...
1 vote
182 views

### Is it safe to use fast/small hash for key identity?

I have to roll database access keys often, but it's important to know which key each system is using in order to avoid unavailability. I want the systems to report that without exposing the key itself,...
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### Why is CRC said to be linear?

It is commonly understood that CRC satisfies the linear identity with respect to the $\oplus$ (XOR) operation: $\operatorname{CRC}(a) \oplus \operatorname{CRC}(b) = \operatorname{CRC}(a \oplus b)$ ...
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### Suggestion : CRC vs SHA1

I need some suggestions about the use of the CRC in my application. I need to be sure about the BIOS run by the CPU. I have a FPGA between the BIOS flash and the CPU that sniff every read performed by ...
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### Authenticating small packets

I intend to authenticate small packets of data, between 16 and 256 bytes each. For some of them encryption will also be required. This will be used on small micro controllers, with RAM sizes ranging ...
1 vote
5k views

### Modifying a [CRC32] checksum protected file [closed]

I dont want to ask for help without showing how far I came by myself, so this is what I have so far: The file of interest is an encrypted/obfuscated .bin script, which cotains information on certain ...
2k views

### Achieving 32-bit verification code with 16-bit CRC? [closed]

I am programming an embedded chip that has a hardware 16-bit CRC module. I have to protect some data bytes $d_0,d_1,...,d_{n-1}$ against corruption caused by sudden loss of power; a 32-bit CRC would ...
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### CRC32 vs. low 32 bits of cryptographic hash

I was having a discussion with a colleague yesterday whose education and experience exceeded mine. He said something yesterday that sounded incorrect to me intuitively, but I don't have the knowledge ...
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### Is there a generic attack on encrypted CRC32 when used as a MAC?

I am examining a protocol that uses CRC32 as a MAC (see note 1) the weaknesses of this method but I would nevertheless like to see if it is just weak or actually relatively easily to break. The ...
4k views

### Is Dropbox's hashing method cryptographically secure?

Dropbox uses CRC32 and md5 to create a checksum of each 4 mb "block" as part of the their compression/file system. I suspect that Dropbox uses an additional cryptographic hash to check if there's a ...
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### Reversing N CRC steps [closed]

Starting from a known CRC result(let's call it CRC1), could I undo the CRC operations for last N bits, so I could obtain the CRC (let's call it CRC2) of the message sequence without the last N bits. \$...
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### Can i modify data "protected" by a CRC16?

There are 100 bytes with a CRC16. However I only know the first 50. I want to change byte 5 from a known value X to another value Y, and fix up the CRC16 to be valid - without knowing bytes 50-100. ...
4k views

### Increased CRC collision probability when adding bits to input message [closed]

The Scenario I have a message string I need to transport over a wireless network that may be unreliable. This message string is about 100 bits long, and is packaged with an 8-bit CRC. When the ...
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8k views

### How do I calculate CRC32 mathematically? [closed]

I want to calcuate the CRC32 algorithm using polynomials directly but I don't know how. I found the generating polynomial listed here https://en.wikipedia.org/wiki/Cyclic_redundancy_check. This ...
4k views

### Finding CRC collisions for specific divisor [closed]

My current textbook (Information Security: Principles and Practice by Mark Stamp) discusses how to determine the CRC of data via long-division, using XOR instead of subtraction to determine the ...
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### Understanding CRC [closed]

There are zillions of articles describing CRC. What can I read to (more deeply) understand what's really going on? Both from an algebraic perspective and a bit-manipulation perspective, I'd like to ...