|CRCs||Scratch 16-bit CRC|
|Sun 16-bit CRC|
CRCs are used in CCITT (Comité Consultatif International Téléphonique et Télégraphique) protocols. Adlerian checksums are faster to compute. For even greater speed you can use a simple XOR addition of all longs in the file/message. MD5 (Message Digest algorithm 5) and SHA-1 (Secure Hash Algorithm 1) digests are cryptographic strength. Which you should use depends on the degree of damage you want to protect against and whether that damage is intentional. CRCs won’t protect you against intentional damage, because the hacker can recompute the embedded checksum or fairly easily fiddle the file to make the checksum come out the same. Making a doctored file come out to the same checksum is very difficult do with MD5 or SHA-1. To prevent doctoring and computing the checksum, you must use digital signing. Applet signing schemes use cryptographic digests to ensure the Applet is unmodified, and truly written by the author advertised.
Some C++ code for computing CRC-16s is part of the CDDTest program part of the EIDEFLAW detecting package.
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