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
With the SFTP, running over an encrypted SSH session, there’s no chance the file contents could get corrupted while transferring. So unless it gets corrupted when reading the local file or writing the remote file, you can be pretty sure that the file was uploaded correctly, if the .put does not throw any error. try: … Read more
Update I added a helper function to create the CRCTable instead of having this enormous literal in the code. It could also be used to create the table once and save it in an object or variable and have the crc32 function use that (or as W3C’s example, check for the existence and create if … Read more
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
Yes. You can see how in zlib’s crc32_combine(). If you have two sequences A and B, then the pure CRC of AB is the exclusive-or of the CRC of A0 and the CRC of 0B, where the 0’s represent a series of zero bytes with the length of the corresponding sequence, i.e. B and A … 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
using (FileStream fs = new FileStream(@”C:\file\location”, FileMode.Open)) using (BufferedStream bs = new BufferedStream(fs)) { using (SHA1Managed sha1 = new SHA1Managed()) { byte[] hash = sha1.ComputeHash(bs); StringBuilder formatted = new StringBuilder(2 * hash.Length); foreach (byte b in hash) { formatted.AppendFormat(“{0:X2}”, b); } } } formatted contains the string representation of the SHA-1 hash. Also, by using … 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
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