Re: [exim] dkim=fail (body hash mismatch; body probably mod…

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Author: Victor Sudakov
Date:  
To: Jeremy Harris, exim-users
Subject: Re: [exim] dkim=fail (body hash mismatch; body probably modified in transit)
Jeremy Harris via Exim-users wrote:
> On 02/12/2022 16:54, Victor Sudakov via Exim-users wrote:
> > I have an exim 4.95 installation sending DKIM-signed mails to two
> > other exim servers. On one of the receiving servers (FreeBSD,exim-4.95_5),
> > I see that the DKIM check is successful:
> >
> > Authentication-Results: XXXXXX;
> >          iprev=pass (www.library.tomsk.ru) smtp.remote-ip=95.170.141.50;
> >          spf=pass smtp.mailfrom=library.tomsk.ru;
> >          dkim=pass header.d=library.tomsk.ru header.s=20221203 header.a=rsa-sha256

> >
> > On the other receiving server (Debian, exim4 4.94.2-7), the very same
> > mail (sent simultaneously to two recipients on XXXXXX and YYYYYY) is
> > reported as having an unsuccessful DKIM check:
> >
> > Authentication-Results: YYYYYY;
> >          iprev=pass (www.library.tomsk.ru) smtp.remote-ip=95.170.141.50;
> >          dkim=fail (body hash mismatch; body probably modified in transit)
> >          header.d=library.tomsk.ru header.s=20221203 header.a=rsa-sha256

>
> Is this consistent for all messages sent to the pair of hosts?
> Or only occasional?


I have sent 10 short messages from the library.tomsk.ru host:

echo "test test" | mail -s "test test" vas@XXXXXX vas@YYYYYY

and its 10 times dkim=pass on FreeBSD and 10 times dkim=fail on Debian
so I guess it's consistent.

However, I've noticed that when I send a larger mail, like

uuencode /usr/bin/vi vi | mail -s "test test" vas@XXXXXX vas@YYYYYY

then 10 of the 10 mails on Debian have dkim=pass. So the message size
or encoding is envolved somehow? What gives?

>
> What libraries do 'exim -d -bV' report for each host?


FreeBSD sender:
Compiler: CLang [10.0.1 (git@???:llvm/llvm-project.git llvmorg-10.0.1-0-gef32c611aa2)]
Probably Berkeley DB version 1.8x (native mode)
Library version: OpenSSL: Compile: OpenSSL 1.1.1l-freebsd  24 Aug 2021
                          Runtime: OpenSSL 1.1.1l-freebsd  24 Aug 2021
                                 : built on: reproducible build, date unspecified
Library version: IDN: Compile: 1.35
                      Runtime: 1.35
Library version: spf2: Compile: 1.2.10
                       Runtime: 1.2.10
Library version: Cyrus SASL: Compile: 2.1.28
                             Runtime: 2.1.28 [Cyrus SASL]
Library version: PCRE: Compile: 8.45
                       Runtime: 8.45 2021-06-15


FreeBSD receiver:

Compiler: CLang [10.0.1 (git@???:llvm/llvm-project.git llvmorg-10.0.1-0-gef32c611aa2)]
Probably Berkeley DB version 1.8x (native mode)
Library version: OpenSSL: Compile: OpenSSL 1.1.1l-freebsd  24 Aug 2021
                          Runtime: OpenSSL 1.1.1l-freebsd  24 Aug 2021
                                 : built on: reproducible build, date unspecified
Library version: IDN: Compile: 1.35
                      Runtime: 1.38
Library version: spf2: Compile: 1.2.10
                       Runtime: 1.2.11
Library version: Cyrus SASL: Compile: 2.1.28
                             Runtime: 2.1.28 [Cyrus SASL]
Library version: PCRE: Compile: 8.45
                       Runtime: 8.45 2021-06-15


Debian receiver YYYYYY:

Compiler: GCC [10.2.1 20210110]
Library version: Glibc: Compile: 2.31
                        Runtime: 2.31
Library version: BDB: Compile: Berkeley DB 5.3.28: (September  9, 2013)
                      Runtime: Berkeley DB 5.3.28: (September  9, 2013)
Library version: GnuTLS: Compile: 3.7.1
                         Runtime: 3.7.1
Library version: IDN2: Compile: 2.3.0
                       Runtime: 2.3.0
Library version: Stringprep: Compile: 1.33
                             Runtime: 1.33
Library version: Cyrus SASL: Compile: 2.1.27
                             Runtime: 2.1.27 [Cyrus SASL]
Library version: PCRE: Compile: 8.39
                       Runtime: 8.39 2016-06-14
Library version: MySQL: Compile: 100510 10.5.10 [mariadb-10.5]
                        Runtime: 100515 10.5.15
Library version: SQLite: Compile: 3.34.1
                         Runtime: 3.34.1


--
Victor Sudakov VAS4-RIPE
http://vas.tomsk.ru/
2:5005/49@fidonet