On Apr 22, 2012, at 16:21, Joshua Root wrote: > On 2012-4-23 06:51 , Ryan Schmidt wrote: >> No, I'm trying to protect against the gzip compression of the tar archive >> varying from generation to generation. gzip compression uses entropy -- >> random numbers. If you have two identical tar archives, and gzip compress >> them with the same settings, the resulting gzip files will not be byte for >> byte identical, and thus they'll have different checksums: >> >> $ sha1sum *.tar >> 92bfe8b02b49b977a18c9f8e8d301a0ef159fe51 1.tar >> 92bfe8b02b49b977a18c9f8e8d301a0ef159fe51 2.tar >> $ gzip 1.tar >> $ gzip 2.tar >> $ sha1sum *.tar.gz >> 39c6beda6851d98295f770a11b8ea122647ae4c8 1.tar.gz >> 7a95ea746e698d367ec155e4387972051e1a2e38 2.tar.gz >> $ > > Nonsense. The gzip files in the above example differ because they > contain files with different names.
Oh. Well, here's a test with the same file names: $ sha1sum */file.tar 92bfe8b02b49b977a18c9f8e8d301a0ef159fe51 1/file.tar 92bfe8b02b49b977a18c9f8e8d301a0ef159fe51 2/file.tar $ gzip 1/file.tar $ gzip 2/file.tar $ sha1sum */file.tar.gz 238d08d9c64af0622abdd6a074b5c3c0b784a238 1/file.tar.gz e398dbc43e65f5bb165876bcb1819b302fe251fd 2/file.tar.gz $ > I haven't looked into it in detail, but I would guess the actual reason > the tarballs end up having different checksums when regenerated is > because of the timestamps. _______________________________________________ macports-dev mailing list macports-dev@lists.macosforge.org http://lists.macosforge.org/mailman/listinfo.cgi/macports-dev
