${alg_bits}
The number of bits in the TLS cipher V8.11 and later
TLS is a protocol implemented with the OpenSSL
library. When the remote site recognizes that the
local sendmail supports the
STARTTLS ESMTP extension, and if policy at the
remote site allows it to, the remote site sends the
STARTTLS command. If that command is accepted by the
local sendmail, the two sides
negotiate a secure connection. Part of the
information determined in this negotiation is the
cipher to use. Once a cipher has been accepted, and
the connection allowed,
sendmail updates the value of
several macros, among which is this ${alg_bits}
macro.
The ${alg_bits}
macro holds as its value the number of bits of the
symmetric encryption in the cipher that was agreed
upon. That value is a text representation of a
positive integer, or, if there was no cipher, the
number zero.
When sendmail logs the start of a TLS session, it does so with a line such as this:
STARTTLS=who, relay=host, version=vers, verify=verify, cipher=cipher, bits= algbits/cbits
Here, the value assigned to this ${alg_bits} macro is
printed following the bits= and before the slash.
The ${alg_bits}
macro is transient. If it is defined in the
configuration file or in the command line, that
definition can be ignored by
sendmail. Note that a
$& prefix
is necessary when you reference this macro in rules
(that is, use $&{alg_bits}, not ${alg_bits}).
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