dovecot - Apr 2023 - https://www.mail-archive.com/dovecot@dovecot.org/msg77000.html

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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> Op 10 apr. 2023 om 18:40 heeft Martin Stenzel <stenzel at bw-host.de>
het volgende geschreven:
> 
> ?
> 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...
> 
Why?
> 
> 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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> On 10/04/2023 15:37 EEST Martin Stenzel <stenzel at bw-host.de>
wrote:
> 
> 
> Hi team,
> regarding:
> https://www.mail-archive.com/dovecot at dovecot.org/msg77000.html
> 
> 
> I have the very same problem.
> 
> 
<snip/>

Hi!

It seems that the ruby openssl module interface has changed slightly, I'll
look into it. We might as well move it to https://github.com/dovecot/tools while
at it.

For what it's worth, it works with ruby2.7 for me.

The reason it looks the same with -k pub and priv, is that the key does not
match, so it just tells you what key to expect. I'll make the output bit
more verbose about this too.

Aki

> 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...
> 
>