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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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Identification of RF hash algorithm [migrated]

I have an unbranded LED lamp with a remote control. I would like to reverse the protocol of the remote but unfortunately I can't create my own packages. The frequency of the remote transceiver is 2....
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1answer
171 views

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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0answers
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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 ...
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1answer
440 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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0answers
294 views

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 ...
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0answers
64 views

Tamperable hash function

I'm wondering if a hash function with the following properties exists. Let's say that I have the hashes of these three strings: ["aaa", "bbb", "ccc"] Is there a way to find the hash of the ...
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1answer
478 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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1answer
121 views

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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1answer
1k views

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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3answers
377 views

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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1answer
104 views

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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2answers
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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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1answer
2k views

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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1answer
141 views

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 ...
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2answers
3k 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 ...
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2answers
983 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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2answers
902 views

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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1answer
2k views

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 ...
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2answers
3k 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 ...
2
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2answers
271 views

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. $...
4
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1answer
794 views

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. ...
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4answers
3k 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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1answer
5k 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 ...
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1answer
2k 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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3answers
3k views

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 ...
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2answers
3k views

Brute forcing CRC-32

I'm working on a cryptosystem which uses IDEA. The designer made the mistake of including a CRC-32B hash of the password unencrypted in the header, so that the system can quickly reject bad passwords....
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4answers
4k views

What alphanumeric string length can be used to guarantee no hash collisions from CRC-64? [closed]

If I'm hashing alphanumeric strings (chars in the set 0-9, a-...