Cryptography Stack Exchange
Cryptography Stack Exchange

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.

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. Such questions may be asked on Stack Overflow instead.

50 questions
17
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2 answers

Why is CRC said to be linear?

It is commonly understood that CRC satisfies the linear identity with respect to the $\oplus$ (XOR) operation: $\operatorname{CRC}(a) \oplus \operatorname{CRC}(b) = \operatorname{CRC}(a \oplus b)$ But after some experimentation and research it…
user9070
9
votes
2 answers

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. Of course, that opens it up to the obvious…
S. Robert James
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9
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4 answers

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

If I'm hashing alphanumeric strings (chars in the set 0-9, a-z, and A-Z) with a CRC-64 hashing function, how long can my strings be while guaranteeing no hash collisions? Stated differently: If I have a set of all CRC-64 checksums computed from…
brandx
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8
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1 answer

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 program will download firmware images from us and…
user42679
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6
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3 answers

Understanding CRC

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 understand it well enough to have an intuitive feel…
S. Robert James
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6
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1 answer

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 packages has only one SHA test-sum, why not to increase…
XuMuK
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5
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1 answer

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. This is possible with the TCP checksum, because…
John
5
votes
2 answers

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?
Hiccup
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5
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1 answer

How do I calculate CRC32 mathematically?

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 corresponds to 0xedb88320 in the example code. Can…
user2558
4
votes
4 answers

Increased CRC collision probability when adding bits to input message

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 message is received, it's validated with the CRC and…
jmbeck
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4
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2 answers

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 didn't mention. I know they use different polynomial…
tansy
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4
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1 answer

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) $$ m = \mathit{Timestamp}\mathbin\Vert M $$ Divide into…
user80551
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4
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1 answer

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 examined protocol has the format more or less…
Antikithira
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3
votes
1 answer

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 the CPU on the BIOS memory. The initial idea was…
haster8558
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3
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2 answers

Achieving 32-bit verification code with 16-bit CRC?

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 provide the level of protection that I need, but…
TonyK
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