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| -rw-r--r-- | doc/doc-docbook/spec.xfpt | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index ad4df88ea..ac95f2680 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -16031,6 +16031,21 @@ The available primes are: Some of these will be too small to be accepted by clients. Some may be too large to be accepted by clients. +The TLS protocol does not negotiate an acceptable size for this; clients tend +to hard-drop connections if what is offered by the server is unacceptable, +whether too large or too small, and there's no provision for the client to +tell the server what these constraints are. Thus, as a server operator, you +need to make an educated guess as to what is most likely to work for your +userbase. + +Some known size constraints suggest that a bit-size in the range 2048 to 2236 +is most likely to maximise interoperability. The upper bound comes from +applications using the Mozilla Network Security Services (NSS) library, which +used to set its &`DH_MAX_P_BITS`& upper-bound to 2236. This affects many +mail user agents (MUAs). The lower bound comes from Debian installs of Exim4 +prior to the 4.80 release, as Debian used to patch Exim to raise the minimum +acceptable bound from 1024 to 2048. + .option tls_on_connect_ports main "string list" unset This option specifies a list of incoming SSMTP (aka SMTPS) ports that should @@ -25686,7 +25701,7 @@ tls_dhparam = none This may also be set to a string identifying a standard prime to be used for DH; if it is set to &`default`& or, for OpenSSL, is unset, then the prime used is &`ike23`&. There are a few standard primes available, see the -documetnation for &%tls_dhparam%& for the complete list. +documentation for &%tls_dhparam%& for the complete list. See the command .code |