opendkim-genkey man page

opendkim-genkey — DKIM filter key generation tool


opendkim-genkey [options]


opendkim-genkey generates (1) a private key for signing messages using opendkim(8) and (2) a DNS TXT record suitable for inclusion in a zone file which publishes the matching public key for use by remote DKIM verifiers.

The filenames of these are based on the selector (see below); the private key will have a suffix of ".private" and the TXT record will have a suffix of ".txt".

Both long and short names are supported for most options.


(--append-domain) Appends the domain name (see -d below) to the label in the generated TXT record, followed by a trailing period. By default it is assumed the domain name is implicit from the context of the zone file, and is therefore not included in the output.
-b bits
(--bits=n) Specifies the size of the key, in bits, to be generated. The default is 1024 which is the value recommended by the DKIM specification.
-d domain
(--domain=string) Names the domain which will use this key for signing. Currently only used in a comment in the TXT record file. The default is "".
-D directory
(--directory=path) Instructs the tool to change to the named directory prior to creating files. By default the current directory is used.
-h algorithms
(--hash-algorithms=name[:name[...]]) Specifies a list of hash algorithms which can be used with this key. By default all hash algorithms are allowed.
Print a help message and exit.
-n note
(--note=string) Includes arbitrary note text in the key record. By default, no such text is included.
(--restricted) Restricts the key for use in e-mail signing only. The default is to allow the key to be used for any service.
-s selector
(--selector=name) Specifies the selector, or name, of the key pair generated. The default is "default".
(--[no]subdomains) Disallows subdomain signing by this key. By default the key record will be generated such that verifiers are told subdomain signing is permitted. Note that for backward compatibility reasons, -S means the same as --nosubdomains.
(--[no]testmode) Indicates the generated key record should be tagged such that verifiers are aware DKIM is in test at the signing domain.
(--verbose) Increase verbose output.
(--version) Print version number and exit.


Requires that the openssl(8) binary be installed and in the executing shell's search path.


This man page covers the version of opendkim-genkey that shipped with version 2.10.3 of OpenDKIM.

See Also

opendkim(8), openssl(8)

RFC6376 - DomainKeys Identified Mail


The Trusted Domain Project