https://www.mail-archive.com/dovecot@dovecot.org/msg77000.html

Martin Stenzel
Mon, 10 Apr 2023 12:37:20 -0000

Hi team,

regarding:

https://www.mail-archive.com/dovecot at dovecot.org/msg77000.html


I have the very same problem.


terve:/tmp #decrypt.rb -k /etc/dovecot/mailcrypt/ecpubkey.pem -f
./1681118363....terve.xy-space.de\,S\=3452\,W\=3515\:2\,S

Key(s) (total: 1)
 ?- Key type ?: EC
 ?- Key digest: a27b201cf7f59f...
 ?- Peer key ?: 04aaca0143208904deced2732aaa...
 ?- Encrypted : 4cde641bff16098b91bfaf66...
 ?- Kd hash ??: 9e229ec6c0...
terve:/tmp #decrypt.rb -k /etc/dovecot/mailcrypt/ecprivkey.pem -f
./16811....terve.xy-space.de\,S\=3452\,W\=3515\:2\,S


Key(s) (total: 1)
 ?- Key type ?: EC
 ?- Key digest: a27b201cf7f59f978bb9b27947f60a9...
 ?- Peer key ?: 04aaca0143208904deced2732aaaf127...
 ?- Encrypted : 4cde641bff16098b91bfaf66c9...
 ?- Kd hash ??: 9e229ec6c09...

terve:/tmp #decrypt.rb -i -k /etc/dovecot/mailcrypt/ecprivkey.pem -f
./1681118...terve.xy-space.de\,S\=3452\,W\=3515\:2
\,S
Version ??????: 2
Flags ????????: AEAD integrity
Header length : 255
Cipher algo ??: aes-256-gcm (2.16.840.1.101.3.4.1.46)
Digest algo ??: sha256 (2.16.840.1.101.3.4.2.1)

Key derivation
 ?- Rounds ???: 2048

...

N. B. Before posting I arbitrarily removed numbers from the output,
maybe paranoid...


Environment:

openSuSE Linux server.

dovecot version 2.3.20

openssl version 1.1.1

ruby version 3.1.2p20

decrypt.rb version
https://gist.github.com/cmouse/882f2e2a60c1e49b7d343f5a6a2721de


This is the way I generated the keys:

openssl ecparam -name prime256v1 -genkey | openssl pkey -out ecprivkey.pem
openssl pkey -in ecprivkey.pem -pubout -out ecpubkey.pem


This is the 10-mailcrypt.conf:

mail_plugins = $mail_plugins mail_crypt

plugin {
 ???#fts_index_fs =
crypt:set_prefix=fscrypt_index:posix:set_prefix=/tmp/fts
 ???mail_crypt_global_private_key = </etc/dovecot/mailcrypt/ecprivkey.pem
 ???mail_crypt_global_public_key = </etc/dovecot/mailcrypt/ecpubkey.pem
 ???mail_crypt_save_version = 2
}

Encryption of incoming (thanks to dovecot-lda), as well as outgoing
mails works perfectly.


But for me it is more a feature than a bug, since now, even as root I am
not able to decrypt users mails.

This serves plausible deniability.


But how can I make sure, that NOBODY ELSE can decrypt with this specific
private key?

Is there ANY OTHER way to decrypt the mails besides the script?


Have a nice Monday, and THANKS for taking your time!

Martin, Cologne


P. S. Did you notice, that as an argument (-k) the results are the same,
both with private and public key?

P.P.S. If i give the "-w" argument and a file name, the file remains
empty, tried even that without success.

P.P.P.S. If I call the script with ruby version 2 it bails out...

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