Dorchester — Mar 14th 2017

Tony raised our understanding of Malware and the ways in which Apple helps defend us from it. His talk focused on macOS but most points are also applicable to iOS. He excluded eMail and Social Media from his talk as these have been covered by others and the vulnerabilities are user-enabled.
Malware, short for Malicious Software, includes viruses, worms, trojan horses, spyware, adware and ‘bots’. All are program code, designed to malevolently disrupt the device for cussedness or financial reward, to gather sensitive information, display unwanted adverts, or to commandeer the device for nefarious activity (bots). The code is often hidden in a regular app. or a text, image or pdf data file. We tend to hear that these are only a problem for Windows and not for Macs so to warn us off complacency, Tony listed known Mac malware from September 2016 to February 2017 when “Patcher” ransomware appeared.

Originally infections were transferred via hard media such a floppy discs, CDs, DVDs and memory sticks, but today the Internet is the main vehicle. By looking at that earlier route, Tony introduced us to the concept of Trust. In those times you would buy your branded software from a reputable shop in a sealed (and expensive) pack with a unique licence. If you bought “unlocked software” on an unpackaged disc, heavily discounted, you were plainly running a risk that malevolent code had been inserted. How can you establish the same Trust in this age of downloaded software? ‘Packets’ of downloaded software do not come by a single route from supplier to buyer but via the multi-route Internet network where it can be compromised. Nowadays software developers can apply digital signatures to their work. Tony likened this to a Roman emperor rolling up a decree and sealing it with wax, the seal being his signature. If broken, it showed the recipient that it could have been tampered with. The digital signature is a key without which no recipient can open the software. It assures that what is received is identical to what was sent. But how do you transfer an exclusive key which cannot be grabbed by a third party? High level mathematics and Prime numbers underlie all encryption and encryption keys. Digital signatures are issued by Apple to registered software developers. Some developers choose not to register with Apple due, in part, to the cost.

Apple have built software into Mac OS including “GateKeeper” which validates digital signatures in downloads, and (since Mountain Lion), “X-Protect” — a built-in virus checker. When Apps are downloaded to a Mac, they are placed in quarantine where Gatekeeper checks the Digital Signature. For those with a damaged (or no) digital signature, Gate Keeper throws up a window either warning users to reject (with no option to open) or advising caution before opening. If you trust the software developer and download from their own website, then you should have sufficient trust to install their software. Note: Gatekeeper only checks downloads from the Internet, not from discs, memory sticks etc.

Flash and Java in Safari are also potential sources of attack so it is important to keep them up to date and set the OS to ask before use. This is set up in Safari Preferences > Security > Plug-in Settings. Turn off unused services. Your router will have a built-in firewall but if you are out and about there is no certainty that another internet connection will be protected so Tony recommends keeping the macOS firewall turned on.

Apple’s system upgrades will nearly always include new security software so don’t leave it too long before installing.

SUMMARY ACTIONS. Check Settings for Gatekeeper and Firewall. Keep macOS up to date, applying upgrades promptly. Minimise usage of Flash and Java, updating directly from Adobe/Oracle and make web sites ask to use them. Download software from reputable sites and always prefer the developer’s own site.

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After the break, Euan explained Anti-aliasing and Unsharp Masks. He reminded us of the difference between Vector and Raster graphics and (for Raster graphics) the significance of image resolution (pixels or dots per inch –– ppi and dpi) and their effect on screen display and print output. The lower the resolution of Raster images the more jagged the edges of any non-vertical or horizontal lines and edges will be displayed or printed. Using easily understood images and fonts, he showed how the jaggedness of raster shapes is smoothed in software by adjusting the intensity of individual pixels/dots along the edges. This adjustment is Anti-aliasing.

Euan then discussed Unsharp Masking. Using clear images, he showed the steps carried out by the software, which blurs the image and makes inverted versions, merging them with the original image, allowing user adjustment of the overall effect. He explained the uses of the Radius, Factor, and Threshold adjustments, and demonstrated these effects on a colour image. Unsharp masking should usually be done after all other image edits have been completed.

Resizing images affects anti-aliasing as well as dpi/ppi, so that the choice of method is important. Using several images to illustrate the results, Euan compared “nearest neighbour”, “bi-linear”, “bi-cubic”, and “Lanczos”. He enlarged a black and white newspaper image with visible printing dots and blurred this image so that the printing dots were no longer visible, and then used Unsharp Mask to restore contrast so that the image, although softer, was still clear overall — impressive.

Comments

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Tony Still said…

After this presentation, I came across a useful summary of macOS security from Apple. For those that are interested, it's here (not as good as my presentation, of course ;-) ).
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