• Some weeks ago, we introduced a 3D printer that takes spools of plastic and melted them into objects like the elephants.

  • But when David was at office hours at Leverett, he met one of your classmates and a friend of Cheng’s (yes I have friends), Michelle, who interned at Formlabs. Their printers use a different technique called stereolithography to print objects. This technique takes a liquid called resin and hits it with a laser to make it solid, while a plate lifts it up slowly until the object is complete. Check out the timelapse in the lecture video, made with single photos taken over the course of several hours!

  • This hardware is available to you, especially if your final project blends together software and the physical world in a creative way!

  • Last night, the Crimson also published an article about how David Johnson is leaving at the end of the academic year. David, who has been senior preceptor for Ec10 for many years, has also been a wonderful mentor to CS50 over the years and often counseled us on running such a large course. We thank and admire you, David Johnson!

  • Unrelatedly, the end of the semester coming up. Let’s see what’s ahead:

    • lecture on Mon 11/10 (you are here)

    • guest lecture on Wed 11/12

      • Steve Ballmer from Microsoft will speak, and if you haven’t already, RSVP at They’ll be checking Harvard IDs at the door!

      • And this video should excite you if you didn’t see the one from last week’s lecture!

    • no lecture on Mon 11/17

    • quiz on Wed 11/19

    • final lecture (and cake!) on Mon 11/24

  • And for the project:

    • status report due on Mon 12/1

    • CS50 Hackathon on Wed 12/3, Thu 12/4

      • Note that you should be closer toward the middle or end of your final project, not the beginning, by this time!

    • CS50 Fair on Mon 12/8

  • And as usual, if you want to join Nick and others at CS50 Lunch on Fri, 11/14 at 1:15pm, RSVP at the usual

  • And if you wish to join Nick and other staff as a member of CS50’s team, we’ll be recruiting for next year’s team, with roles like:

Password Management09:31

  • In other other news, David got a spam email this morning, that somehow slipped through Gmail’s filters:

    Spam email
    • That nice blue link looks really enticing, but the forms that such links lead to should have enough warning signs, like their look, or typos, that you stop before you fill them out:

      Spam portal
  • We’ll look at some other examples today to see how we, humans, can be more conscious of security.

  • Even these days, lots of us use the same password for every website, and that makes sense because one password is a lot easier to remember than a bunch of passwords. But the risk is that if one website was hacked, then all of your accounts would be compromised.

  • We suggest a password manager, like the following:



    • …​

      Basically, these programs remember your passwords for you, encrypting them on your local hard drive, and fill out online login forms for you automatically, after asking for your master password, which unlocks all of those individual passwords.

    • And definitely don’t write down passwords on Post-It notes!

  • In fact, the other day David was ordering something from Edible Arrangements, and when he tried to log in with his password manager, it warned him that their website was insecure:

    Edible Arrangements login screen
    • And we can confirm this by looking at the top left, where it says http instead of https.

  • Maybe there was something else to this story, so David opened the trusty Developer Tools and took a look at the request the page sent: