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Exim TLS 和安全 SMTP

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Exim TLS 和安全 SMTP

我正在转换现有的邮件服务器以支持客户的加密 SMTP，但我遇到了这个难题，几乎没有有用的日志数据来帮助我转发。使用常规未加密的 SMTP 时一切都正常；只有在尝试使用加密 SMTP 时，事情才会变得糟糕。


我的 exim 配置文件包含以下内容：

# Allow any client to use TLS
tls_advertise_hosts                       =  *

# Specify the location of the Exim server's TLS certificate and private key.
tls_certificate                           =  /etc/exim/exim.crt
tls_privatekey                            =  /etc/exim/exim.key


最初，进出口银行出现为确保正常运行，我可以安全地连接到邮件服务器并验证自己的身份，但就在我进入 SMTP 会话中的收件人部分后，连接断开。使用未加密的连接时不会发生此问题。


为了测试安全 SMTP，我使用以下命令：

openssl s_client -starttls smtp -crlf -connect localhost:25


这是我得到的输出：

CONNECTED(00000003)
depth=0 C = ZA, etc, etc
verify error:num=18:self signed certificate
verify return:1
depth=0 C = ZA, etc, etc
verify return:1
---
Certificate chain
 0 s:/C=ZA/etc,etc
   i:/C=ZA/etc,etc
---
Server certificate
-----BEGIN CERTIFICATE-----
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXX==
-----END CERTIFICATE-----
subject=/C=ZA/etc,etc
---
No client certificate CA names sent
---
SSL handshake has read 1275 bytes and written 444 bytes
---
New, TLSv1/SSLv3, Cipher is AES256-SHA
Server public key is 1024 bit
Secure Renegotiation IS supported
Compression: zlib compression
Expansion: zlib compression
SSL-Session:
    Protocol  : TLSv1
    Cipher    : AES256-SHA
    Session-ID: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
    Session-ID-ctx: 
    Master-Key: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    TLS session ticket:
    0000 - d0 cd ff b6 0c a2 fb 6c-f6 69 dc 0b a7 aa f3 1a   .......l.i......
    0010 - 10 76 75 05 15 d8 8c 21-cb eb b8 ae ec 34 7d b3   .vu....!.....4}.
    0020 - 7a bf f0 d6 7d df 26 27-41 1e d1 2a 35 bf 2f 0c   z...}.&'A..*5./.
    0030 - 25 6a 32 15 6e 53 d2 30-31 1b d9 60 e6 11 20 73   %j2.nS.01..`.. s
    0040 - 57 e3 76 96 e7 7e dc da-98 f2 cc a7 e5 58 62 b2   W.v..~.......Xb.
    0050 - ec db 58 91 16 14 18 ff-15 64 d6 66 1f 75 92 96   ..X......d.f.u..
    0060 - 65 43 f8 2c 4a 42 81 41-0c 2f 46 84 38 0c c5 e0   eC.,JB.A./F.8...
    0070 - 8d 7b d7 7e 12 0e 28 ca-f0 f9 b5 d0 b2 a6 ab 66   .{.~..(........f
    0080 - f8 c5 33 e3 cb 16 f5 76-8f e7 49 0c 49 69 31 43   ..3....v..I.Ii1C
    0090 - 05 25 dc 75 3a 07 13 91-63 ff 13 fd b0 2c 9f 8b   .%.u:...c....,..

    Compression: 1 (zlib compression)
    Start Time: 1315250595
    Timeout   : 300 (sec)
    Verify return code: 18 (self signed certificate)
---
250 HELP
HELO localhost
250 OK
MAIL FROM:[email protected]
250 OK
RCPT TO:[email protected]
RENEGOTIATING
depth=0 C = ZA, etc, etc
verify error:num=18:self signed certificate
verify return:1
depth=0 C = ZA, etc, etc
verify return:1
421 lost input connection
read:errno=0

我已经用垃圾数据替换了上述输出中的电子邮件地址和组织树，因为这无关紧要，因为我使用常规 SMTP 时不会遇到同样的问题。无论我尝试从本地主机还是从外部源进行连接，上述事务都会发生。我还应该注意，我使用的是使用 OpenSSL 生成的自签名证书。此外，在上面的例子中没有身份验证数据，因为我是从本地主机执行测试的，这允许所有邮件而无需身份验证。

正如您在上面的输出中看到的，Exim 似乎在发出字符串“RENEGOTIATING”期间/之后中断。

由于我在 SMTP 会话期间收到的输出没有太大帮助，我还尝试在调试 +all 模式下运行 Exim。为了简洁起见，我不会发布完整的 SMTP 事务，因为整个会话都很正常，直到我指定收件人地址为止。这是我输入收件人地址并按下回车键后获得的 Exim 调试数据的确切片段：

21:42:10  7425 SSL info: before accept initialization
21:42:10  7425 SSL info: before accept initialization
21:42:10  7425 SSL info: SSLv3 read client hello A
21:42:10  7425 SSL info: SSLv3 write server hello A
21:42:10  7425 SSL info: SSLv3 write certificate A
21:42:10  7425 SSL info: SSLv3 write server done A
21:42:10  7425 SSL info: SSLv3 flush data
21:42:10  7425 SSL info: SSLv3 read client key exchange A
21:42:10  7425 SSL info: SSLv3 read finished A
21:42:10  7425 SSL info: SSLv3 write session ticket A
21:42:10  7425 SSL info: SSLv3 write change cipher spec A
21:42:10  7425 SSL info: SSLv3 write finished A
21:42:10  7425 SSL info: SSLv3 flush data
21:42:10  7425 SSL info: SSL negotiation finished successfully
21:42:10  7425 SSL info: SSL negotiation finished successfully
21:42:10  7425 Got SSL error 2
21:42:10  7425 SMTP>> 421 lost input connection
21:42:10  7425 tls_do_write(1db4020, 48)
21:42:10  7425 SSL_write(SSL, 1db4020, 48)
21:42:10  7425 outbytes=48 error=0
21:42:10  7425 LOG: lost_incoming_connection MAIN
21:42:10  7425   unexpected disconnection while reading SMTP command from (localhost) [127.0.0.1]
21:42:10  7425 search_tidyup called
21:42:10  7194 child 7425 ended: status=0x100
21:42:10  7194 0 SMTP accept processes now running
21:42:10  7194 Listening...

答案1

我通过谷歌搜索花了 30 秒找到了这个“openssl s_client 正在重新协商”： s_client 的 R“功能”

总结一下 - 在 s_client 会话中按“R”会导致 openssl 重新协商。请尝试输入“rcpt to:”而不是“RCPT TO”。

您还可以尝试更适合 SMTP 特定测试的工具，例如Tony Finch 的 smtpc或者斯瓦克斯。

答案2

为了要求exim我在身份验证时进行加密设置/etc/exim/exim.conf：

auth_advertise_hosts = ${if eq{$tls_cipher}{}{}{*}}

我也强制tls 1.2：

openssl_options = +no_sslv2 +no_sslv3 +no_tlsv1 +no_tlsv1_1

在两台相同的exim服务器之间，我注意到一台使用AES-GCM，另一台使用ChaCha20-Poly1305加密，但不知道为什么。使用的加密方案取决于是否host具有AES硬件加速在`cpu中。

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