On 04/20/2017 05:40 PM, Paul Wouters wrote:
On Thu, 20 Apr 2017, Rui Costa wrote: I want to send you an encrypted email. I need your key. I can send a plaintext email asking you for the key. I have to hope that it really reached you and that it is you who gave me the key and that the key was not modified in transport.
There are free email cert companies. This email is signed by one (unless the list server strips them out like it used to). Your MUA now knows my public key.
This is how it is done. I know it works with Thunderbird and Outlook.To send a signed email, I only had to configure my MUA once. Thunderbird and Outlook always S/MIME signs all of my email with the free cert I use.
You send me a signed (not encrypted) email from a *mutually trusted* cert source. Your MUA signed it with your private key, because that's how its done. Only your public key can verify it.
My MUA examines the email, extracts your public key that is included in an S/MIME signed email, verifies it was signed by the mutually trusted cert source. I now know the 'From' email address matches the signature, the content, and the only way your MUA could have generated those sequence of bits, is that it was signed by your matching private key.
I now have your public key. Verified by a email message signature that could have only been signed by the matching private key, which validate against the trusted cert source. Who cares if the world sees your public key - that the point of a public key.
If someone were to modify the message in transit (only some of the headers are used in the signature verification), the signature will fail to validate. Then my MUA would tag it as bad signature and should be un-trusted.
Thunderbird signifies a good signature with an image of a letter, with a red seal.
When my MUA validates that the signature matches the email content, then the recipient MUA knows nothing was altered, including the public key, which it keeps.
Thunderbird and Outlook collect these certs by default. I do not have to do anything. I can even export them to a file, and import them into another MUA.
I can now send you an encrypted email, encrypted with my private key and your public key. Only your MUA can open it with your private key and my public key, and in that process, also validates it.
-- Doug Royer - (http://DougRoyer.US http://goo.gl/yrxJTu ) DouglasRoyer@xxxxxxxxx 714-989-6135
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