Something that should be noted here, and that most people overlook completely, is the fact, that the TCP checksum is actually a very poor checksum. The TCP checksum is a 16-bit ones-complement sum of the data. This sum will catch any burst error of 15 bits or less, and all 16-bit burst errors except for … Read more
This code is from the CMupdater, from the CyanogenMod 10.2 android ROM. It tests the downloaded ROMs into the updater App. code: https://github.com/CyanogenMod/android_packages_apps_CMUpdater/blob/cm-10.2/src/com/cyanogenmod/updater/utils/MD5.java It works like a charm: /* * Copyright (C) 2012 The CyanogenMod Project * * * Licensed under the GNU GPLv2 license * * The text of the license can be found … Read more
In Windows (command prompt) you can use CertUtil, here is the syntax: CertUtil [Options] -hashfile InFile [HashAlgorithm] for syntax explanation type in cmd: CertUtil -hashfile -? example: CertUtil -hashfile C:\myFile.txt MD5 default is SHA1 it supports: MD2, MD4, MD5, SHA1, SHA256, SHA384, SHA512. Unfortunately no CRC32 as Unix shell does. Here is a link if … Read more
What you describe is called a collision. Collisions necessarily exist, since SHA-1 accepts many more distinct messages as input that it can produce distinct outputs (SHA-1 may eat any string of bits up to 2^64 bits, but outputs only 160 bits; thus, at least one output value must pop up several times). This observation is … Read more
The CertUtil is a pre-installed Windows utility, that can be used to generate hash checksums: CertUtil -hashfile pathToFileToCheck [HashAlgorithm] HashAlgorithm choices: MD2 MD4 MD5 SHA1 SHA256 SHA384 SHA512 So for example, the following generates an MD5 checksum for the file C:\TEMP\MyDataFile.img: CertUtil -hashfile C:\TEMP\MyDataFile.img MD5 To get output similar to *Nix systems you can add … Read more
The polynomial for CRC32 is: x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x + 1 Wikipedia CRC calculation Or in hex and binary: 0x 01 04 C1 1D B7 1 0000 0100 1100 0001 0001 1101 … Read more
I would say that a checksum is necessarily a hashcode. However, not all hashcodes make good checksums. A checksum has a special purpose — it verifies or checks the integrity of data (some can go beyond that by allowing for error-correction). “Good” checksums are easy to compute, and can detect many types of data corruptions … Read more
Git prefixes the object with “blob “, followed by the length (as a human-readable integer), followed by a NUL character $ echo -e ‘blob 14\0Hello, World!’ | shasum 8ab686eafeb1f44702738c8b0f24f2567c36da6d Source: http://alblue.bandlem.com/2011/08/git-tip-of-week-objects.html
The problem here is that SHA256Managed reads 4096 bytes at a time (inherit from FileStream and override Read(byte[], int, int) to see how much it reads from the filestream), which is too small a buffer for disk IO. To speed things up (2 minutes for hashing 2 Gb file on my machine with SHA256, 1 … Read more
The slowest possible method is to compare two files byte by byte. The fastest I’ve been able to come up with is a similar comparison, but instead of one byte at a time, you would use an array of bytes sized to Int64, and then compare the resulting numbers. Here’s what I came up with: … Read more