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I am using Thunderbird with EnigMAIL, have my own keys generated, and downloaded the receivers public key. Now when I send the e-mail, I understand that my system encrypts the message using THEIR public key, resulting in only THEM being able to decrypt it.

Why does my TB ask for my password phrase?

From the Thunderbird documentation:

Sending a digitally signed and / or encrypted email [...] - If your email address is associated with a PGP key, the message will be encrypted with that key. If the email address is not associated with a PGP key, you will be prompted to select a key from a list. [...]

That is the point I do not understand, why would it need my password phrase when sending the mail? I thought it would need only the receivers pub key to do so, or is there something else to it?

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You are not only encrypting the message with the user their public key, but also with your own private key. This way, you can ensure only the intended receiver can read the email and the receiver is sure only you could have sent the email.

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  • Okay, to help me understand this: how is it verified that it was actually me who signed that mail? Is it something being able to decrypt with the public key, or what is that?
    – SinisterMJ
    Nov 19, 2013 at 11:06
  • I just read the PGP wiki entry: (about digital signature) "To do so, PGP computes a hash (also called a message digest) from the plaintext and then creates the digital signature from that hash using the sender's private key." That hash can be created by anyone, so does the public key come into play there, and if so, how?
    – SinisterMJ
    Nov 19, 2013 at 11:16
  • A hash of the message is generated. Then the privatey key is used to create a signature from that hash. Now, using the public key, one can decrypt the signature to get the hash, which can then be verified against the message. Nov 19, 2013 at 12:05
  • @SinisterMJ - It seems you don't understand how PGP works. This question has a great answer superuser.com/questions/16160/…
    – Ramhound
    Nov 19, 2013 at 12:12
  • I do understand how PGP works, I did not know that its used to sign emails as well. Thats why I wondered when it asked me for my password phrase when sending an email, since the mathematics only require the receivers pub key.
    – SinisterMJ
    Nov 19, 2013 at 14:30

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