option.
+.new
+.option dane_require_tls_ciphers smtp string&!! unset
+.cindex "TLS" "requiring specific ciphers for DANE"
+.cindex "cipher" "requiring specific"
+.cindex DANE "TLS ciphers"
+This option may be used to override &%tls_require_ciphers%& for connections
+where DANE has been determined to be in effect.
+If not set, then &%tls_require_ciphers%& will be used.
+Normal SMTP delivery is not able to make strong demands of TLS cipher
+configuration, because delivery will fall back to plaintext. Once DANE has
+been determined to be in effect, there is no plaintext fallback and making the
+TLS cipherlist configuration stronger will increase security, rather than
+counter-intuitively decreasing it.
+If the option expands to be empty or is forced to fail, then it will
+be treated as unset and &%tls_require_ciphers%& will be used instead.
+.wen
+
+
.option data_timeout smtp time 5m
This sets a timeout for the transmission of each block in the data portion of
the message. As a result, the overall timeout for a message depends on the size
to this server, its A record, its TLSA record and any associated CNAME records must all be covered by
DNSSEC.
2) add TLSA DNS records. These say what the server certificate for a TLS connection should be.
-3) offer a server certificate, or certificate chain, in TLS connections which is traceable to the one
-defined by (one of?) the TSLA records
+3) offer a server certificate, or certificate chain, in TLS connections which is is anchored by one of the TLSA records.
There are no changes to Exim specific to server-side operation of DANE.
Support for client-side operation of DANE can be included at compile time by defining SUPPORT_DANE=yes
those who use &%hosts_require_ocsp%&, should consider the interaction with DANE in their OCSP settings.
-For client-side DANE there are two new smtp transport options, &%hosts_try_dane%& and &%hosts_require_dane%&.
-The latter variant will result in failure if the target host is not DNSSEC-secured.
+For client-side DANE there are three new smtp transport options, &%hosts_try_dane%&, &%hosts_require_dane%&
+and &%dane_require_tls_ciphers%&.
+The require variant will result in failure if the target host is not DNSSEC-secured.
DANE will only be usable if the target host has DNSSEC-secured MX, A and TLSA records.
will be required for the host. If it does not, the host will not
be used; there is no fallback to non-DANE or non-TLS.
+If DANE is requested and usable, then the TLS cipher list configuration
+prefers to use the option &%dane_require_tls_ciphers%& and falls
+back to &%tls_require_ciphers%& only if that is unset.
+This lets you configure "decent crypto" for DANE and "better than nothing
+crypto" as the default. Note though that while GnuTLS lets the string control
+which versions of TLS/SSL will be negotiated, OpenSSL does not and you're
+limited to ciphersuite constraints.
+
If DANE is requested and useable (see above) the following transport options are ignored:
.code
hosts_require_tls
The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present
for EC keys.
-As of writing, producing EC key materials is not well supported
-by the major libraries. OpenSSL 1.1.1 and GnuTLS 3.6.0 can create private keys:
+OpenSSL 1.1.1 and GnuTLS 3.6.0 can create Ed25519 private keys:
.code
openssl genpkey -algorithm ed25519 -out dkim_ed25519.private
certtool --generate-privkey --key-type=ed25519 --outfile=dkim_ed25519.private
.endd
-To help in producing the required public key value for a DNS record
-the release package &_util/_& directory contains source for a utility
-buildable with GnuTLS 3.6.0;
-use it like this:
+To produce the required public key value for a DNS record:
.code
-ed25519_privkey_pem_to_pubkey_raw_b64 dkim_ed25519.private
+openssl pkey -outform DER -pubout -in dkim_ed25519.private | tail -c +13 | base64
+certtool --load_privkey=dkim_ed25519.private --pubkey_info --outder | tail -c +13 | base64
.endd
.wen
.vitem &%permerror%&
This indicates a syntax error in the SPF record of the queried domain.
-You may deny messages when this occurs. (Changed in 4.83)
+You may deny messages when this occurs.
.vitem &%temperror%&
This indicates a temporary error during all processing, including Exim's
SPF processing. You may defer messages when this occurs.
-(Changed in 4.83)
-
-.vitem &%err_temp%&
-Same as permerror, deprecated in 4.83, will be removed in a future release.
-
-.vitem &%err_perm%&
-Same as temperror, deprecated in 4.83, will be removed in a future release.
.endlist
You can prefix each string with an exclamation mark to invert
git://git.exim.org / exim.git / blobdiff