First lesson: learn your tools. apt-cache search ssl | grep kde gives you kdebase-crypto - KDE crypto control module. Note that in many cases, crypto capabilities are disaggregated due to restrictions in many jurisdictions on import/export or merely access to strong crypto.

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You'll want aptitude (as Greg indicated). apt-cache allows searching archives for terms (only within text fields of the package description, however). There's a package search utility at the Debian website (under packages). And apt-file lets you search for any file in any Debian package, installed or not. You'll need to update the apt-file archive periodically, of course.