[gnupg.git] / README

                    GnuPG - The GNU Privacy Guard
                   -------------------------------
                            Version 0.9

    GnuPG is now in Beta test and you should report all bugs to the
    mailing list (see below).  The 0.9.x versions are mainly released
    to fix all remaining serious bugs.  As soon as version 1.0 is out,
    development will continue with a 1.1 series and bug fixes for the
    1.0 version are released as needed.

    GnuPG works best on GNU/Linux or *BSD.  Other Unices are
    also supported but not as good tested as those Freenix ones.
    Please verify the tar file; there is a PGP2 and a GnuPG/PGP5
    signature available. My PGP2 key is well known and published in
    the "Global Trust Register for 1998", ISBN 0-9532397-0-5.

    I have included my pubring as "g10/pubring.asc", which contains
    the key used to make GnuPG signatures:
    "pub  1024D/57548DCD 1998-07-07 Werner Koch (gnupg sig) <dd9jn@gnu.org>"
    "Key fingerprint = 6BD9 050F D8FC 941B 4341  2DCC 68B7 AB89 5754 8DCD"

    My new DSA key is:
    "pub  1024D/621CC013 1998-07-07 Werner Koch <werner.koch@guug.de>"
    "Key fingerprint = ECAF 7590 EB34 43B5 C7CF  3ACB 6C7E E1B8 621C C013"

    You may want add it to your GnuPG pubring and use it in the future to
    verify new releases.  Because you verified this README file and
    _checked_that_it_is_really_my PGP2 key 0C9857A5, you can be sure
    that the above fingerprints are correct.

    Please subscribe to g10@net.lut.ac.uk by sending a mail with
    the word "subscribe" in the body to "g10-request@net.lut.ac.uk".
    This mailing list is a closed one (only subscribers are allowed
    to post) to avoid misuse by folks who don't know the Netiquette
    and trash you mailspool with commercial junk.

    See the file COPYING for copyright and warranty information.

    GnuPG is in compliance with RFC2440 (OpenPGP), see doc/OpenPGP for
    details.

    Due to the fact that GnuPG does not use use any patented algorithm,
    it cannot be compatible with PGP2 versions; PGP 2.x does only use
    IDEA (which is patented worldwide) and RSA (which is patented in
    the United States until Sep 20, 2000).

    The default algorithms are now DSA and ElGamal.  ElGamal for signing
    is still available, but due to the larger size of such signatures it
    is depreciated (Please note that the GnuPG implementation of ElGamal
    signatures is *not* insecure).  Symmetric algorithms are: 3DES,
    Blowfish and CAST5 (Twofish will come soon),  available digest
    algorithms are MD5, RIPEMD160, SHA1 and TIGER/192.


    Installation
    ------------

    Please read the file INSTALL!

    Here is a quick summary:

    1)  "./configure"

    2) "make"

    3) "make install"

    4) You end up with the binaries "gpg" and "gpgm" in /usr/local/bin.

    5) Optional, but suggested: install the binary "gpg" as suid root.



    Intro
    -----
    This is a brief overview how to use GnuPG - it is highly suggested
    that you read the manual^H^H^H more information about the use
    of cryptography.  GnuPG is only the technical tool to do it and
    the security highly depends on that YOU KNOW WHAT YOU ARE DOING.

    If you already have a DSA key from PGP 5 (they call them DH/ElGamal)
    you can simply copy the pgp keyrings over the GnuPG keyrings after
    running gpg once, so that it can create the correct directory.

    The normal way to create a key is:

        gpg --gen-key

    This asks some questions and then starts key generation. To create
    good random numbers for the key parameters, GnuPG needs to gather
    enough noise (entropy) from your system.  If you see no progress
    during key generation you should start some other activities such
    as mouse moves or hitting on the CTRL and SHIFT keys.

    Generate a key ONLY on a machine where you have direct physical
    access - don't do it over the network or on a machine used also
    by others - especially if you have no access to the root account.

    When you are asked for a passphrase; use a good one which you can easy
    remember. Don't make the passphrase too long because you have to
    type it for every decryption or signing; but - AND THIS IS VERY
    IMPORTANT - use a good one which is not easily guessable as the
    security of the whole system relies on your secret key and the
    passphrase is used to protect this secret key in case someone was
    able to get access to your secret keyring. A good way to select
    a passphrase is to figure out a short nonsense sentence which makes
    some sense for you and modify it by inserting extra spaces, non-letters
    and changing the case of some characters - this is really easy to
    remember especially if you associate some pictures with it.

    Then you should create a revocation certificate in case someone
    gets knowledge of your secret key or you forgot your passphrase:

        gpg --gen-revoke your_user_id

    Run this command and store it away; output is always ASCII armored,
    so that you can print it and (hopefully never) re-create it if
    your electronic media fails.

    Now you can use your key to create digital signatures:

        gpg -s file

    This creates a file file.gpg which is compressed and has a signature
    attached.

        gpg -sa file

    Same as above, but creates the file.asc which is ascii armored and
    and ready for sending by mail.  Note: It is better to use your
    mailers features to create signatures (The mailer uses GnuPG to do
    this) because the mailer has the ability to MIME encode such
    signatures - but this is not a security issue.

        gpg -s -o out file

    Creates a signature of file, but writes the output to the file "out".

    Everyone who knows your public key (you can and should publish
    your key by putting it on a key server, a web page or in your .plan
    file) is now able to check whether you really signed this text;

        gpg --verify file

    GnuPG now checks whether the signature is valid and prints an
    appropriate message.  If the signature is good, you know at least
    that the person (or machine) has access to the secret key which
    corresponds to the published public key.
    If you run gpg without an option it will verify the signature and
    create a new file which is identical to the original file.  gpg
    can also run as a filter, so that you can pipe data to verify
    trough it:

        cat signed-file | gpg | wc -l

    will check the signature of signed-file and then display the
    number of lines in the original file.

    To send a message encrypted to someone you can use this:

        gpg -e -r heine file

    This encrypts file with the public key of the user "heine" and
    writes it to "file.gpg"

        echo "hallo" | gpg -ea -r heine | mail heine

    Ditto, but encrypts "hallo\n" and mails it as ascii armored message
    to the user with the mail address heine.

        gpg -se -r heine file

    This encrypts file with the public key of "heine" and writes it
    to "file.gpg" after signing it with your user id.

        gpg -se -r heine -u Suttner file

    Ditto, but sign the file with your alternative user id "Suttner"


    GnuPG has some options to help you publish public keys; this is
    called "exporting" a key:

        gpg --export >all-my-keys

    exports all the keys in the keyring and writes them (in a binary format)
    to all-my-keys.  You may then mail "all-my-keys" as an MIME attachment
    to someone else or put it on an FTP server. To export only some
    user IDs, you give them as arguments on the command line.

    To mail a public key or put it on a web page you have to create
    the key in ASCII armored format:

        gpg --export --armor | mail panther@tiger.int

    This will send all your public keys to your friend panther.

    If you have received a key from someone else you can put it
    into your public keyring; is called "importing":

        gpg --import [filenames]

    New keys are appended to your keyring and already existing
    keys are updated. Note that GnuPG does not allow keys which
    are not self-signed by the user.

    Because anyone can claim that the public key belongs to her
    we must have some way to check that the public key really belongs
    to the owner.  This can be achieved by comparing the key during
    a phone call.  Sure, it is not very easy to compare a binary file
    by reading the complete hex dump of the file - GnuPG (and nearly
    every other program used for management of cryptographic keys)
    provides other solutions:

        gpg --fingerprint <username>

    prints the so called "fingerprint" of the given username; this
    is a sequence of hex bytes (which you may have noticed in mail
    sigs or on business cards) which uniquely identify the public
    key - two different keys will always have different fingerprints.
    It is easy to compare this fingerprint by phone and I suggest
    that you print your fingerprint on the back of your business
    card.

    If you don't know the owner of the public key you are in trouble;
    but wait: A friend of you knows someone who knows someone who
    has met the owner of the public key at some computer conference.
    So all the persons between you and the public key holder may now
    act as introducer to you; this is done by signing the keys and
    thereby certifying the other keys.  If you then trust all the
    introducers to correctly sign other keys, you can be be sure that
    the other key really belongs to the one who claims so.

    There are 2 steps to validate a target key:
        1. First check that there is a complete chain
           of signed keys from the public key you want to use
           and your key and verify each signature.
        2. Make sure that you have full trust in the certificates
           of all the introduces between the public key holder and
           you.
    Step 2 is the more complicated part because there is no easy way
    for a computer to decide who is trustworthy and who is not.  GnuPG
    leaves this decision to you and will ask you for a trust value
    (here also referenced as the owner-trust of a key) for every key
    needed to check the chain of certificates.  You may choose from:
      a) "I don't know" - then it is not possible to use any
         of the chains of certificates, in which this key is used
         as an introducer, to validate the target key.  Use this if
         you don't know the introducer.
      b) "I do not trust" - Use this if you know that the introducer
         does not do a good job in certifying other keys.  The effect
         is the same as with a) but for a) you may later want to
         change the value because you got new information about this
         introducer.
      c) "I trust marginally" - Use this if you assume that the
         introducer knows what he is doing.  Together with some
         other marginally trusted keys, GnuPG validates the target
         key then as good.
      d) "I fully trust" - Use this if you really know that this
         introducer does a good job when certifying other keys.
         If all the introducer are of this trust value, GnuPG
         normally needs only one chain of signatures to validate
         a target key okay. (But this may be adjusted with the help
         of some options).
    These information are confidential because they give your
    personal opinion on the trustworthy of someone else.  Therefore
    this data is not stored in the keyring but in the "trustdb"
    (~/.gnupg/trustdb.gpg).  Do not assign a high trust value just
    because the introducer is a friend of you - decide how far she
    understands all the implications of key signatures and you may
    want to tell him more about public key cryptography so you
    can later change the trust value you assigned.

    Okay, here is how GnuPG helps you in key management:  Most stuff is
    done with the --edit-key  command:

        gpg --edit-key <keyid or username>

    GnuPG displays some information about the key and then prompts
    for a command (enter "help" to see a list of commands and see
    the man page for a more detailed explanation).  To sign a key
    you select the user ID you want to sign by entering the number
    which is displayed in the leftmost column (or do nothing if the
    key has only one user ID) and then enter the command "sign" and
    follow all the prompts.  When you are ready, give the command
    "save" (or use "quit" to cancel your actions).

    If you want to sign the key with another user ID of yours, you
    must give an "-u" option on the command line together with the
    "--edit-key".

    Normally you want to sign only one user ID because GnuPG
    does only use one and this keeps the public key certificate
    small.  Because such key signatures are very important you
    should make sure that the signators of your key sign a user ID
    which is very likely to stay for a long time - choose one with an
    email address you have full control of or do not enter an email
    address at all.  In future GnuPG will have a way to tell which
    user ID is the one with an email address you prefer - because
    you have no signatures on this email address it is easy to change
    this address.  Remember: Your signators sign your public key (the
    primary one) together with one od your user IDs - so it is not possible
    to change the user ID later without voiding all the signatures.

    Tip: If you hear about a key signing party on a computer conference
    join it because this is a very convenient way to get your key
    certified (But remember that signatures have nothing to to with the
    trust you assign to a key).


    7 Ways to Specify a User ID
    --------------------------
    There are several ways to specify a user ID, here are some examples:

    * Only by the short keyid (prepend a zero if it begins with A..F):

        "234567C4"
        "0F34E556E"
        "01347A56A"
        "0xAB123456

    * By a complete keyid:

        "234AABBCC34567C4"
        "0F323456784E56EAB"
        "01AB3FED1347A5612"
        "0x234AABBCC34567C4"

    * By a fingerprint:

        "1234343434343434C434343434343434"
        "123434343434343C3434343434343734349A3434"
        "0E12343434343434343434EAB3484343434343434"

      The first one is MD5 the others are ripemd160 or sha1.

    * By an exact string:

        "=Heinrich Heine <heinrichh@uni-duesseldorf.de>"

    * By an email address:

        "<heinrichh@uni-duesseldorf.de>"

    * By the Local ID (from the trust DB):

        "#34"

      This may be used by a MUA to specify an exact key after selecting
      a key from GnuPG (by the use of a special option or an extra utility)

    * Or by the usual substring:

        "Heine"
        "*Heine"

      The '*' indicates substring search explicitly.


    Batch mode
    ----------
    If you use the option "--batch", GnuPG runs in non-interactive mode and
    never prompts for input data.  This does not even allow entering the
    passphrase; until we have a better solution (something like ssh-agent),
    you can use the option "--passphrase-fd n", which works like PGPs
    PGPPASSFD.

    Batch mode also causes GnuPG to terminate as soon as a BAD signature is
    detected.


    Exit status
    -----------
    GnuPG returns with an exit status of 1 if in batch mode and a bad signature
    has been detected or 2 or higher for all other errors.  You should parse
    stderr or better the output of the fd specified with --status-fd to get
    detailed information about the errors.


    Esoteric commands
    -----------------

        gpg --list-packets datafile

    Use this to list the contents of a data file. If the file is encrypted
    you are asked for the passphrase, so that GnuPG is able to look at the
    inner structure of a encrypted packet.  This command should be able
    to list all kinds of rfc2440 messages.

        gpgm --list-trustdb

    List the contents of the trust DB in a human readable format

        gpgm --list-trustdb  <usernames>

    List the tree of certificates for the given usernames

        gpgm --list-trust-path  username

    List the possible trust paths for the given username. The length
    of such a trust path is limited by the option --max-cert-depth
    which defaults to 5.

    For more options/commands see the man page or use "gpg --help".


    Other Notes
    -----------

    The primary FTP site is "ftp://ftp.gnupg.org/pub/gcrypt/"
    The primary WWW page is "http://www.gnupg.org"

    See http://www.gnugp.org/mirrors.html for a list of FTP mirrors
    and use them if possible.

    Please direct bug reports to <gnupg-bugs@gnu.org> or better
    post them to the mailing list <g10@net.lut.ac.uk> (this is a
    closed list - subscribe before posting, see above (~line 33)).
    Please direct questions about GnuPG to the mailing list or
    one of the pgp newsgroups; this gives me more time to improve
    GnuPG.  Commercial support for GnuPG will be availabe soon.

    Have fun and remember: Echelon is looking at you kid.