These options control what GnuPG is compliant to. Only one of these options may be active at a time. Note that the default setting of this is nearly always the correct one. See the INTEROPERABILITY WITH OTHER OPENPGP PROGRAMS section below before using one of these options.
Use standard GnuPG behavior. This is essentially OpenPGP behavior (see --openpgp), but with some additional workarounds for common compatibility problems in different versions of PGP. This is the default option, so it is not generally needed, but it may be useful to override a different compliance option in the gpg.conf file.
Reset all packet, cipher and digest options to strict OpenPGP behavior. Use this option to reset all previous options like --s2k-*, --cipher-algo, --digest-algo and --compress-algo to OpenPGP compliant values. All PGP workarounds are disabled.
Reset all packet, cipher and digest options to strict RFC-4880 behavior. Note that this is currently the same thing as --openpgp.
Reset all packet, cipher and digest options to strict RFC-2440 behavior.
Try to be more RFC-1991 (PGP 2.x) compliant. This option is deprecated will be removed in GnuPG 2.1.
Set up all options to be as PGP 2.x compliant as possible, and warn if an action is taken (e.g. encrypting to a non-RSA key) that will create a message that PGP 2.x will not be able to handle. Note that ‘PGP 2.x’ here means ‘MIT PGP 2.6.2’. There are other versions of PGP 2.x available, but the MIT release is a good common baseline.
This option implies --rfc1991 --disable-mdc --no-force-v4-certs --escape-from-lines --force-v3-sigs --allow-weak-digest-algos --cipher-algo IDEA --digest-algo MD5 --compress-algo ZIP. It also disables --textmode when encrypting.
This option is deprecated will be removed in GnuPG 2.1. The reason for dropping PGP-2 support is that the PGP 2 format is not anymore considered safe (for example due to the use of the broken MD5 algorithm). Note that the decryption of PGP-2 created messages will continue to work.
Set up all options to be as PGP 6 compliant as possible. This restricts you to the ciphers IDEA (if the IDEA plugin is installed), 3DES, and CAST5, the hashes MD5, SHA1 and RIPEMD160, and the compression algorithms none and ZIP. This also disables –throw-keyids, and making signatures with signing subkeys as PGP 6 does not understand signatures made by signing subkeys.
This option implies --disable-mdc --escape-from-lines.
Set up all options to be as PGP 7 compliant as possible. This is identical to --pgp6 except that MDCs are not disabled, and the list of allowable ciphers is expanded to add AES128, AES192, AES256, and TWOFISH.
Set up all options to be as PGP 8 compliant as possible. PGP 8 is a lot closer to the OpenPGP standard than previous versions of PGP, so all this does is disable --throw-keyids and set --escape-from-lines. All algorithms are allowed except for the SHA224, SHA384, and SHA512 digests.