Zitat von Martijn Brinkers <[email protected]>:
I was just thinking of the following situation which actually happens in my case. I still use a very old email address I have already for a long time ([email protected]). Pobox is only a forwarding service so email sent to my Pobox account is forwarded to my Djigzo email address. When someone sends encrypted email to my Pobox account using an email client it will be encrypted with the certificate for the Pobox email address. The email however will be forwarded to my Djigzo address. The gateway can decrypt the message because the gateway contains the private key of the Pobox account. When strict mode will be enabled, the gateway will refuse to decrypt the message because there will be a mismatch between recipient email address and certificate email address. Whether or not this is a good think (not in my case) it of course up to the gateway admin.I would suggest the following: - For "non-domain-encryption" eg. automatic private-key selection only use a key if the recipient address also matches - If one would like settings like above or domain-encryption it is necessaey to manual select the keys considered by Djigzo for decryption and asign it to the user (address) or domain (domain-encryption)Yes agree. So the above settings will be used in the "strict mode".In any case incoming encrypted mail should be split to single recipient to simplify the handling and allow a mix of both. The percentage of encrypted mail which has also multiple recipients should be low enough to not bother with the additional overhead.Yes splitting the mail into multiple emails might be the easiest approach. However this also makes the gateway vulnerable to a DOS attack. Suppose someone sends an encrypted message to 1000 recipients. If the message is split up, it will explode into 1000 messages which need to be handled/decrypted individually. In real life situations an encrypted email can have a lot of recipients when domain encryption is used (for example when a mailing is sent to multiple recipients). I'm therefore thinking to split the message in two (only in strict mode) if needed. If there is no decryption certificate for one or more users, split the message into a message that will be decrypted and into a message that won't be encrypted. This way you only require two messages no matter how many recipients there are. I think I don't have to decrypt the complete message. I only need to decrypt the encrypted session keys to see whether there is a valid certificate for the recipient.
This is the same problem any MTA will have. Postfix by default limit the number of recipients per mail to 100... What i don't found out yet is if the domain-encryption feature can be set on the receiver side or if it is only triggered by the sender, using one of the recipients valid certificates to encrypt mail for many different recipients. So is it a sender or a recipient "policy". I would for sure like to control on my end (receiver) if i like cross-usage of certificates/keys, but it looks like all is needed is a sender able split certificate usage from recipient address?? In case i got it right the answer will be yes, we need a switch to turn off this behaviour and splitting the messages in a part with valid recipient<-->certificate pairs and a part without, which will not be decrypted will be a way to go.
Regards Andreas
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