• First, we poll the audience with a question: “Is your phone secure?”
    • About a third of the audience responded for each of “Yes”, “No”, and “Unsure”.
  • The passcode to our phones might be four digits, longer, or nothing at all.
  • Some of us might think that our password is more secure because they are random.
  • The most common passwords as of 2020, unfortunately, are easy to guess:
    1. 123456
    2. 123456789
    3. picture1
    4. password
    5. 12345678
    6. 111111
    7. 123123
    8. 12345
    9. 1234567890
    10. senha
      • This translates to “password” in Portuguese.
  • If we have one of these passwords ourselves, it would be easy for someone to break into our account or device, since they’re most likely to try these passwords first.
  • So, we can start to quantify how secure our phones are, by quantifying how secure our passwords are.
  • With a 4-digit passcode, we have 10,000 possible passcodes, from 0000 to 9999. But a computer can generate all of them quickly, in just a few seconds.
  • And someone can perform a brute-force attack, where they try all possible passwords until the correct one is found.
    • An adversary can even build a robot to tap all possible passcodes on a phone screen.
  • We can demonstrate this by writing a program that prints out all possible products, or permuations, of 4-digit passcodes, in a programming language called Python:
    from string import digits
    from itertools import product
    for passcode in product(digits, repeat=4):
    $ python
    0 0 0 0
    0 0 0 1
    9 9 9 8
    9 9 9 9
    • This program takes less than a second to run.
    • We can imagine that an adversary might plug a cable into a phone, and use a computer with code to try all possible passcodes very quickly.
  • With more digits, it will take longer for our passcode to be guessed, raising the cost for our adversary.
  • We can also use a 4-letter passcode. Since we have 26 different letters possible for each place, and each of them can be uppercase or lowercase, we would have 52 x 52 x 52 x 52 possibilities, or more than 7 million possible passcodes.
  • We can change our program to use letters instead of digits:
    from string import ascii_letters
    from itertools import product
    for passcode in product(ascii_letters, repeat=4):
    $ python
    a a a a
    a a a b
    Z Z Z Y
    Z Z Z Z
    • Now this program takes more than a minute to run.
  • We can expand our passcode to use any combination of characters, like letters, numbers, and symbols like ! or #.
  • On a typical keyboard, we’ll have 32 symbols, in addition to 26 uppercase letters, 26 lowercase letters, and 10 numbers, for a total of 94 different symbols. So if we have an 8-character passcode, we’ll be able to choose between 94 x 94 x 94 x 94 x 94 x 94 x 94 x 94 possibilities, which is over 6 quadrillion.
    • If each passcode takes a second to try, it would take more than 193,000 years to try all possibilities.
  • We’ll change our program to use every character:
    from string import ascii_letters, digits, punctuation
    from itertools import product
    for passcode in product(ascii_letters + digits + punctuation, repeat=8):
    • Now, this program will take much longer to run.
  • Longer passwords are harder to crack, or discover, but they are more difficult to remember.
  • On many devices, like an iPhone or Android, trying to log in incorrectly too many times in a row will lock us out from further attempts, telling us to try again in a minute or more. It turns out that this is a security feature, slowing down our adversaries who might be trying to guess our passcode. Now, even with 10,000 possibilities for a 4-digit passcode, this might take 10,000 minutes or more.
  • Two-factor authentication refers to the use of an additional format of information to log in, such as a one-time use code from a message or app. Since this tends to be something we have, in addition to what we know (our username and password), it’s even more difficult for adversaries to log into our account.
  • Password managers are applications that store login information for us, so instead of remembering many different, complex passwords, we only need to remember a single master password. Some popular ones include:
    • Credential Manager in Windows
    • Keychain in macOS
    • 1Password
    • LastPass
  • Our password manager can generate, save, and fill long, unique passwords for all of our other accounts.
  • The downside of a password manager might be a greater risk to us, if our master password is discovered or forgotten. Then, we’d lose all of our accounts at once.

Email, private mode

  • In Gmail, there is new feature called “Confidential mode”, where we are able to send emails and “Recipients won’t have the option to forward, copy, print, or download this email.”
  • But this is a bit misleading, since we can still take a screenshot of the email, or even a photo of our computer’s screen.
  • Our browsers, too, might provide an “incognito mode” or “private mode”, where our browsing history and other pieces of data aren’t saved locally.
  • But the websites we visit and our internet service provider might still see what we’re visiting.


  • Encryption is the scrambling of information so that it can’t be read without a key to decrypt it.
  • The phrase T H I S W A S C S 5 0, for example, might be simply encrypted to U I J T X B T D T 5 0, by rotating each letter once.
  • https:// is a secure, encrypted way for browsers to communicate with web pages, without anyone in between able to read the contents.
  • End-to-end encryption means that our messages are encrypted between us and who we are talking to, so even if we are using a third-party chat or video service, the companies in between are not able to decrypt, or read the contents of our communications.
  • Zoom, for example, had previously advertised end-to-end encryption, but only implemented it as encryption between us and Zoom. Only recently have they rolled out true end-to-end encryption between the participants in a meeting, but some features won’t work as a result, like cloud recording and phone call-in.
  • To summarize, here are a few suggestions we have, to be more secure:
    1. Use a password manager
    2. Use two-factor authentication
    3. Use (end-to-end) encryption