Hi, Two questions really, one is that I can't enable TLS1.3 whatever I try. Running CentOS8 with OpenSSL v1.1.1k-FIPS and Postfix v3.5.8, I confirm that TLS1.3 ciphers are available:
# openssl version OpenSSL 1.1.1k FIPS 25 Mar 2021 # postconf -T compile-version OpenSSL 1.1.1k FIPS 25 Mar 2021 # postconf -T run-version OpenSSL 1.1.1k FIPS 25 Mar 2021 # openssl ciphers -v TLS_AES_256_GCM_SHA384 TLSv1.3 Kx=any Au=any Enc=AESGCM(256) Mac=AEAD TLS_AES_128_GCM_SHA256 TLSv1.3 Kx=any Au=any Enc=AESGCM(128) Mac=AEAD etc. Relevant configuration for port 465 (implicit TLS): # postconf smtpd_tls_cert_file = /path/to/crt smtpd_tls_ciphers = medium smtpd_tls_exclude_ciphers = smtpd_tls_key_file = /path/to/key smtpd_tls_mandatory_ciphers = medium smtpd_tls_mandatory_exclude_ciphers = smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1 smtpd_tls_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1 tls_medium_cipherlist = TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-CHACHA20-POLY1305 smtpd_tls_security_level = encrypt smtpd_tls_wrappermode = yes Trying to connect using TLS1.3 on a client that supports both TLS1.3 ciphersuites, I get: $ openssl s_client -connect server.hostname:465 -tls1_3 Connecting to [IPADDRESS] CONNECTED(00000003) 40879BE5F97F0000:error:0A00042E:SSL routines:ssl3_read_bytes:tlsv1 alert protocol version:ssl/record/rec_layer_s3.c:861:SSL alert number 70 Has this something to do with FIPS mode? I don't think so because the ciphers show up in OpenSSL. Why is TLS1.3 not getting enabled? Second question came up while fixing a blocked outbound port 25 with my ISP. I've noticed that mail gets sent to DANE enabled servers, I suppose because it uses port 587 using STARTTLS. I wonder if postfix allows sending mail over the recommended implicit TLS port 465 between mail servers? The documentation isn't very clear on the distinction between (implicit) TLS and STARTTLS, but setting smtp_tls_wrappermode=yes would force using implicit TLS (right?), while I want to use opportunistic implicit TLS (with fallback to STARTTLS, it's better than nothing) which can be enforced by DANE enabled servers. Kind regards, Taco de Wolff
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