GnuPG - The GNU Privacy Guard ------------------------------- Version 0.9.8 GnuPG is now in Beta test and you should report all bugs to the mailing list (see below). The 0.9.x versions are released mainly 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 as needed. GnuPG works best on GNU/Linux or *BSD. Other Unices are also supported but are not as well tested as the Free Unices. Please verify the tar file with the PGP2 or OpenPGP signatures provided. 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) " "Key fingerprint = 6BD9 050F D8FC 941B 4341 2DCC 68B7 AB89 5754 8DCD" You may want to add this DSA key 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 quite sure that the above fingerprint is correct. Please subscribe to announce@gnupg.org by sending a mail with a subject of "subscribe" to "announce-request@gnupg.org". If you have problems, please subscribe to "gnupg-users@gnupg.org" by sending mail with the subject "subscribe" to "gnupg-users-request@gnupg.org" and ask there. The gnupg.org domain is hosted in Germany to avoid possible legal problems (technical advices may count as a violation of ITAR). See the file COPYING for copyright and warranty information. GnuPG is in compliance with RFC2440 (OpenPGP), see doc/OpenPGP for details. Because GnuPG does not use use any patented algorithm it cannot be compatible with PGP2 versions. PGP 2.x uses only IDEA (which is patented worldwide) and RSA (which is patented in the United States until Sep 20, 2000). The default algorithms are DSA and ElGamal. ElGamal for signing is still available, but because of the larger size of such signatures it is deprecated (Please note that the GnuPG implementation of ElGamal signatures is *not* insecure). Symmetric algorithms are: 3DES, Blowfish, CAST5 and Twofish (GnuPG does not yet create Twofish encrypted messages because there no agreement in the OpenPG WG on how to use it together with a MDC algorithm) Digest algorithms available 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 a "gpg" binary in /usr/local/bin. Note: Because some programs rely on the existence of a binary named "gpgm"; you should install a symbolic link from gpgm to gpg: $ cd /usr/local/bin; ln -s gpg gpgm 5) To avoid swapping out of sensitive data, you can install "gpg" as suid root. If you don't do so, you may want to add the option "no-secmem-warning" to ~/.gnupg/options Introduction ------------ This is a brief overview how to use GnuPG - it is strongly suggested that you read the manual^H^H^H more information about the use of cryptography. GnuPG is only a tool, secure results require 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 to 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 that is not easily to guess because the security of the whole system relies on your secret key and the passphrase that protects it when someone gains 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. Next, 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 the revocation certificate away. The 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 a file "file.asc" which is ASCII armored and and ready for sending by mail. 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 that is identical to the original. gpg can also run as a filter, so that you can pipe data to verify trough it cat signed-file | gpg | wc -l which 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 gpg -e -r heine file This encrypts "file" with the public key of the user "heine" and writes it to "file.gpg" echo "hello" | gpg -ea -r heine | mail heine Ditto, but encrypts "hello\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, thus 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. This is called "importing" gpg --import [filenames] New keys are appended to your keyring and already existing keys are updated. Note that GnuPG does not import keys that are not self-signed. Because anyone can claim that a public key belongs to her we must have some way to check that a 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 prints the so called "fingerprint" of the given username which is a sequence of hex bytes (which you may have noticed in mail sigs or on business cards) that uniquely identifies the public key - different keys will always have different fingerprints. It is easy to compare fingerprints by phone and I suggest that you print your fingerprint on the back of your business card. To see the fingerprints of the secondary keys, you can give the command twice; but this is normally not needed. If you don't know the owner of the public key you are in trouble. Suppose however that friend of yours knows someone who knows someone who has met the owner of the public key at some computer conference. Suppose that all the people between you and the public key holder may now act as introducers to you. Introducers signing keys thereby certify that they know the owner of the keys they sign. If you then trust all the introducers to have correctly signed other keys, you can be be sure that the other key really belongs to the one who claims to own it.. There are 2 steps to validate a 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). This information is confidential because it gives your personal opinion on the trustworthiness 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 yours - decide how well she understands the implications of key signatures and you may want to tell her more about public key cryptography so you can later change the trust value you assigned. Okay, here is how GnuPG helps you with key management. Most stuff is done with the --edit-key command gpg --edit-key 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 that 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 of your user IDs, 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 uses only one and this keeps the public key certificate small. Because such key signatures are very important you should make sure that the signatories 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 signatories sign your public key (the primary one) together with one of 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). 8 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 " * By an email address: "" * By word match "+Heinrich Heine duesseldorf" All words must match excatly (not case sensitive) and appear in any order in the user ID. Words are any sequences of letters, digits, the underscore and characters with bit 7 set. * 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 using 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 list all kinds of rfc2440 messages. gpgm --list-trustdb List the contents of the trust DB in a human readable format gpgm --list-trustdb 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.gnupg.org/mirrors.html for a list of FTP mirrors and use them if possible. To avoid possible legal problems we have decided, not to use the normal www.gnu.org webserver. Please direct bug reports to or post them direct to the mailing list . Please direct questions about GnuPG to the users mailing list or one of the pgp newsgroups and give me more time to improve GnuPG. Commercial support for GnuPG is also available; please see the GNU service directory or search other resources. Have fun and remember: Echelon is looking at you kid.