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[liberationtech] My design to implement PGP in commercial email system

Percy Alpha percyalpha at gmail.com
Sun Jul 28 16:45:57 PDT 2013


PGP is great for privacy but rather hard to use for common users. I came up
with a simple design that can be implement in main-string email system
while preserving the usability.

Take Gmail for example.
First Google should adopt zero-knowledge password proof for its account
while asking users to choose recovery questions. To recover password, users
will answer 3 secret questions and the password is encrypted with the
answers. This ensures that users can recover password and get old emails
back without letting Google know the password.

Then when users first log into Gmail, the browser will generate the keypair
using JavaScript locally and encrypt the secret key with login
password(with PBKDF2, etc). Then the user will upload the encrypted secret
key and plain public key to Google. Because Google doesn't know your
password, Google cannot server you a fake secret key, even though you
download your encrypted secret key from Google every time you login.

When the users tries to send an email to another Gmail user B for the first
time, B's public key will be downloaded from Google and signed by A. Any
subsequent times when A tries to send email to B, A will not only download
B's key from Google but also verifies the authenticity of B's key. This
prevents MITM attack if Google is hacked or forced by law enforcement. (For
advanced users, Google can present the option to manually verify the public
key for the first email. )

To send email between Gmail and Hotmail, Google should be able to request a
Hotmail user's public key from Microsoft server. To prevent spam, Microsoft
should return some random public key for non-exist account and perhaps
always return this fake public key for this non-exist account to prevent
cross reference.

The only downside of this approach is that email providers are not able to
filter spam or provide related Ads based on email content. Even this might
be solved in the future because of private outsourced computation.


Percy Alpha(PGP <https://en.greatfire.org/contact#alt>)
GreatFire.org Team
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