may not be as bad as it appears

may not be as bad as it appears

Posted Aug 18, 2004 18:47 UTC (Wed) by ncm (subscriber, #165)
In reply to: may not be as bad as it appears by ajax
Parent article: Crypto researchers abuzz over flaws (News.com)

In principle it only takes 20 bytes of carefully-chosen garbage added to any text to give a chosen SHA-1 signature, once you've broken it.

It's often pretty easy to find a place to put that much extra stuff, buried in an ELF section or debug annotation of an executable, in extra compression table entries of a tarball, even in text of a diff that you know patch will skip, and that a human would ignore knowing that patch skips it--e.g. in a .sig.

If it must be base64, you need 30 bytes, instead; or 40 bytes of hex, or 70 decimal digits. 14 common lower-case four-letter English words suffice.

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