4 ms·

Weird, I talked to the guy who invented the crypto scheme for ZIP and he said he invented the CRC algorithm for it as well. I wonder if there's more backstory

• AlotOfReading 4y ago
  That's a very strange claim. As far as I know, the same CRC has been used for ZIP since it was invented by the PKWARE guys in the 80s. Moreover, no one deeply understood the properties and tradeoffs of various CRCs the way we do now, so everyone used largely identical algorithms with only trivial variations. Phil Katz did the same and reused the same polynomial that was in ethernet and dozens of other standards, which in turn had originated from this 1975 report: https://apps.dtic.mil/sti/pdfs/ADA013939.pdf https://apps.dtic.mil/sti/pdfs/ADA013939.pdf He wasn't even the first to put a CRC in an archive format, as the predecessor format ARC had a CRC-16 doing the same thing.
  • 13of40 4y ago
    Ah, OK, I looked in my email and it was the guy who invented the encryption scheme, but he said "Yes, I invented it [referring to the encryption]. It wasn't based on anything else, except that it used the same CRC he [Phil] was already using in zip." (As a historical note, he also said the crypto scheme was intended to be exportable, which at that time meant "intentionally weak".)
  • carbonbee 4y ago
    I think what OP meant to write: the zip encryption algorithm is a custom stream cypher that uses crc32 as the main building block. (It's a very bad cypher, vulnerable to known plaintext and other attacks, don't use it for anything except light scrambling).
    • mappu 4y ago
      Nowadays most zip programs will default to using AES (in the way WinZip invented) instead of ZipCrypto.