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Man Pages


Manual Reference Pages  -  PGPIN (1)

NAME

pgp - Pretty Good Privacy encryption system

CONTENTS

Synopsis
Description
Environment
Files
Note
Caveats
Diagnostics
Bugs
Authors

SYNOPSIS

pgp [options] pgpfile

pgp -e [options] file user ...

DESCRIPTION

PGP (Pretty Good Privacy) is a public key encryption package to protect E-mail and data files. It lets you communicate securely with people you’ve never met, with no secure channels needed for prior exchange of keys. It’s well featured and fast, with sophisticated key management, digital signatures, data compression, and good ergonomic design. If you really want to learn how to use it properly, it’s best to read the full documentation that comes with the system, which is very complete. This is a "quick start" guide and reference manual; it is necessarily incomplete, and assumes you are already familiar with most of the basic concepts, including the concepts behind public key cryptography.

    Terminology

user id: an ascii string used to identify a user. User IDs tend to look like "John Q. Public <jqp@xyzcorp.com>"; please try sticking to that format. When giving a user id to PGP, you may specify any unique (case-insensitive) substring. E.g. john, or jqp@xyz.

pass phrase: the secret string used to conventionally encipher your private key. It’s important that this be kept secret.

keyring: a file containing a set of public or secret keys. Default names for public and secret rings are "pubring.pgp" and "secring.pgp" respectively.

ascii armor: the ascii radix 64 format PGP uses for transmitting messages over channels like E-Mail; similar in concept to uuencoding.

    Command summary

To see a quick command usage summary for PGP, just type:
pgp -h

To encrypt a plaintext file with the recipient’s public key:
pgp -e textfile her_userid ...
To sign a plaintext file with your secret key:
pgp -s textfile [-u your_userid]

To sign a plaintext file with your secret key, and then encrypt it with the recipient’s public key:
pgp -es textfile her_userid ... [-u your_userid]
To create a signature certificate that is detached from the document:
pgp -sb textfile [-u your_userid]
To encrypt a plaintext file with just conventional cryptography, type:
pgp -c textfile
To decrypt an encrypted file, or to check the signature integrity of a signed file:
pgp ciphertextfile [-o plaintextfile]
To see a quick summary of PGP’s key-management commands, just type:
pgp -k

To generate your own unique public/secret key pair:
pgp -kg
To add a public or secret key file’s contents to your public or secret key ring:
pgp -ka keyfile [keyring]
To remove a key from your public key ring:
pgp -kr userid [keyring]
To extract (copy) a key from your public or secret key ring:
pgp -kx[a] userid keyfile [keyring]
To view the contents of your public key ring:
pgp -kv[v] [userid] [keyring]
To view the "fingerprint" of a public key, to help verify it over the telephone with its owner:
pgp -kvc [userid] [keyring]

To view the contents and check the certifying signatures of your public key ring:
pgp -kc [userid] [keyring]
To edit the pass phrase for or add a userid to your secret key:
pgp -ke userid [keyring]
To edit the trust parameters for a public key:
pgp -ke userid [keyring]
To remove a key or just a userid from your public key ring:
pgp -kr userid [keyring]

To sign and certify someone else’s public key on your public key ring:
pgp -ks her_userid [-u your_userid] [keyring]
To remove selected signatures from a userid on a keyring:
pgp -krs userid [keyring]

Command options that can be used in combination with other command options (sometimes even spelling interesting words):
To produce a ciphertext file in ASCII radix-64 format, just add the -a option when encrypting or signing a message or extracting a key:
pgp -sea textfile her_userid
pgp -kxa userid keyfile [keyring]
To wipe out the plaintext file after producing the ciphertext file, just add the -w (wipe) option when encrypting or signing a message:
pgp -sew message.txt her_userid
To specify that a plaintext file contains ASCII text, not binary, and should be converted to recipient’s local text line conventions, add the -t (text) option to other options:
pgp -seat message.txt her_userid
To view the decrypted plaintext output on your screen (like the Unix-style "more" command), without writing it to a file, use the -m (more) option while decrypting:
pgp -m ciphertextfile
To specify that the recipient’s decrypted plaintext will be shown only on her screen and cannot be saved to disk, add the -m option:
pgp -steam message.txt her_userid
To recover the original plaintext filename while decrypting, add the -p option:
pgp -p ciphertextfile
To use a Unix-style filter mode, reading from standard input and writing to standard output, add the -f option:
pgp -feast her_userid <inputfile >outputfile

    The Config File

PGP uses a configuration database that is stored in the file "config.txt"; please see the manual for complete details. Blank lines and lines beginning with "#" are comments. Options take string, numeric, or boolean values. The boolean values are "on" and "off". These options can also be specified on the command line, using a syntax such as +armor=on. Keywords can be abbreviated to unique prefixes. Keywords are not case-sensitive. "=on" is assumed for boolean options if nothing is specified. Some highlights:

MYNAME - Default User ID for Making Signatures
Default setting: MYNAME = ""
The configuration parameter MYNAME specifies the default user ID to use to select the secret key for making signatures. If MYNAME is not defined, the most recent secret key you installed on your secret key ring is used. The user may also override this setting by specifying a user ID on the PGP command line with the -u option.

TEXTMODE - Assuming Plaintext is a Text File
Default setting: TEXTMODE = off
The configuration parameter TEXTMODE is equivalent to the -t command line option. If enabled, it causes PGP to assume the plaintext is a text file, not a binary file, and converts it to "canonical text" before encrypting it. Canonical text has a carriage return and a linefeed at the end of each line of text.

This mode is automatically turned off if PGP detects that the plaintext file contains 8-bit binary data. Thus, it is safe to leave enabled at all times.

ARMOR - Enable ASCII Armor Output

Default setting: ARMOR = off

The configuration parameter ARMOR is equivalent to the -a command line option. If enabled, it causes PGP to emit ciphertext or keys in ASCII Radix-64 format suitable for transporting through E-mail channels. Output files are named with the ".asc" extension.

If you tend to use PGP mostly for E-mail, it may be a good idea to enable this parameter.

ARMORLINES - Size of ASCII Armor Multipart Files

Default setting: ARMORLINES = 720

For large ASCII armor files, PGP splits them into files named ".asc1", ".asc2", ".asc3", etc. so as not to choke mailers, which typically starts to happen around 50,000 bytes. This specifies the number of (64-byte) lines to place in each file. If set to 0, PGP will not split ASCII armor files.

CLEARSIG - Enable Clear-Signed Output

Default setting: CLEARSIG = on

Normally, a signed and ASCII-armored PGP message is gibberish, even though the text is not encrypted. This prevents munging by mailers, but requires PGP to simply read the message.

If CLEARSIG is enabled, then when signing and ASCII-armoring a text file, PGP uses a different format that includes the plaintext in human-readable form. Lines beginning with "-" are quoted with "- ". To cope with some of the stupider mailers in the world, lines beginning with "From" are also quoted, and trailing whitespace on lines is stripped. PGP will remove the quoting if you use it to decrypt the message, but the trailing whitespace is not recovered. This is still useful enough to be enabled by default.

ENCRYPTTOSELF - Add MYNAME to Recipients List

Default setting: ENCRYPTTOSELF = off

If this is emabled, MYNAME will be implcitly added to the list of recipients for any message you encrypt with a public key. Since in this case, MYNAME is looked up in the public keyring, it is important that it unambiguously specify the right key.

LANGUAGE - Language To Use

Default setting: LANGUAGE = en

If you want to use a different language, and translations are in the language.txt file, setting this option will cause PGP’s messages to appear in a different language. If a translation for a message is not available, it appears in english.

If you look at the supplied language.txt file, the format should be obvious.

CHARSET - Character Set

Default setting: CHARSET = noconv

PGP tries to translate all text-mode messages into the ISO Latin-1 alphabet, or the KOI-8 alphabet for cyrillic alphabets. This setting indicates the native character set, so PGP can do the translation. Options are noconv, latin1 or koi8, indicating that no translation should be done; cp850, indicating that IBM PC code page 850 mappings should be used; ascii, indicating that a minimal ASCII subset should be used; and alt_codes, indicating that the IBM PC alt codes should be used for the cyrillic alphabet.

KEEPBINARY - Preserve Intermediate .pgp File

Default setting: KEEPBINARY = off

If KEEPBINARY is enabled, then PGP will produce a .pgp file in addition to a .asc file when ASCII armor is enabled.

TMP - Temporary file directory

Default setting: TMP = ""

PGP produces temporary files while decrypting a message. This is the directory they are stored in. If not specified in the config file, the environment variable TMP is used, or the current directory. It helps security somewhat if this is not a publicly-readable directory. A local file system is also a good idea.

COMPRESS - Compress Plaintext Before Encrypting

Default setting: COMPRESS = on

PGP usually compresses the plaintext before encrypting it, so it will have less to encrypt and the file you send will be smaller. It also makes cryptanalysis harder. This is usually only turned off for debugging purposes.

PAGER - Select Shell Command to Display Pager Output

Default setting: PAGER = ""

If set, PGP uses this program to view files when the -m option is specified. By default, PGP uses a simple builtin pager.

SHOWPASS - Echo Pass Phrase During Entry

Default setting: SHOWPASS = off

If someone is unable to type a long pass phrase reliably without seeing it, this can be turned on, at the cost of security.

INTERACTIVE - Prompt Before Adding Each Key

Default setting: INTERACTIVE = off

By default, when given a file containing new keys, PGP asks if you would like to add them to your public key ring. Since adding keys does not imply that you trust them, adding more just wakes up space. If this option is set, PGP asks about each key in a key file.

VERBOSE - Level of Detail Printed

Default setting: VERBOSE = 1

When set to 0, PGP only prints messages that are necessary or indicate an error. When set to 2, PGP prints a significant amount of debugging information describing what it’s doing. Values above 2 have no effect.

PUBRING - Public Key Ring Location

Default setting: PUBRING = $PGPPATH/pubring.pgp

This is the path name to the public key ring to use.

SECRING - Secret Key Ring Location

Default setting: SECRING = $PGPPATH/secring.pgp

This is the path name to the secret key ring to use.

BAKRING - Backup Secret Key Ring

Default setting: BAKRING = ""

If this is set, when checking your key ring (pgp -kc), PGP will compare the normal secret key ring against the given backup copy, usually kept on write-protected removable media. This is to protect against wholesale modifications to your key rings in a spoofing attack.

RANDSEED - Random Number Seed File

Default setting: RANDSEED = $PGPPATH/randseed.bin

This is the path to a random seed file which is part of PGP’s random number generation algorithm, used to generate session keys. While PGP goes to great lengths to use every available source of randomness in generating session keys, this file is part of the process and protecting it from disclosure is desirable.

COMMENT - ASCII Armor Comment

Default setting: COMMENT = ""

If set to a non-empty string, the value of this variable is printed in the header of ASCII armor files, preceded by "Comment: ".

LEGAL_KLUDGE - Incompatibility with PGP versions prior to 2.6

Default setting: LEGAL_KLUDGE = on

If set, PGP will generate keys and messages in a new format that cannot be read by PGP 2.5 and earlier versions.

    Key certification

PGP employs a system where users specify trusted users who may sign other people’s public keys. It is important that you understand how this mechanism works; a full description is in the manual.

Important: The manual also describes how to generate and send a "key compromise" certificate that tells readers that your private key has been compromised. If your key has been compromised, please read the manual section on key compromise certificates and how to create them; the faster you send out a key compromise certificate, the smaller the window of opportunity for "bad guys" to send forged messages.

    Important Hints

PGP automatically tries compressing your input file; there is little point in precompressing input for transmission.

PGP "ascii armor" is only needed on the outer transmitted message; as an example, if you are, say, sending a public key to someone else and you are for some reason signing it, simply armor the outer message; it’s better to sign the binary form of the key.

    Foreign Languages

PGP is easily customized for foreign language help and error messages; it has been translated into a number of non-english languages. See the manual for details on the file "language.txt".

ENVIRONMENT

PGP uses several special files for its purposes, such as your standard key ring files "pubring.pgp" and "secring.pgp", the random number seed file "randseed.bin", the PGP configuration file "config.txt", and the foreign language string translation file "language.txt". These special files can be kept in any directory, by setting the environment variable "PGPPATH" to the desired pathname. If PGPPATH remains undefined, these special files are assumed to be in the current directory.

Normally, PGP prompts the user to type a pass phrase whenever PGP needs a pass phrase to unlock a secret key. But it is possible to store the pass phrase in an environment variable from your operating system’s command shell. The environment variable PGPPASS can be used to hold the pass phrase that PGP attempts to use first. If the pass phrase stored in PGPPASS is incorrect, PGP recovers by prompting the user for the correct pass phrase. This dangerous feature makes your life more convenient if you have to regularly deal with a large number of incoming messages addressed to your secret key, by eliminating the need for you to repeatedly type in your pass phrase every time you run PGP. This is a very dangerous feature; on UNIX it is trivial to read someone else’s environment using the ps(1) command. If you are contemplating using this feature, be sure to read the sections "How to Protect Secret Keys from Disclosure" and "Exposure on Multi-user Systems" in the full PGP manual.

If the environment variable PGPPASSFD is defined, it must have a numeric value, which PGP uses as a file descriptor number to read a pass phrase from. This is done before anything else, so it can be combined with an input file on standard input. This is mainly for use by shell scripts, since under Unix it is difficult to read the contents of other people’s pipes.

RETURN VALUE

PGP returns a 0 to the shell on success, and a nonzero error code on failure. See the source code for details on nonzero status return values.

FILES



*.pgp                         ciphertext, signature, or key file
*.asc                         ascii armor file
/usr/local/lib/config.txt     system-wide configuration file
$PGPPATH/config.txt           per-user configuration file
$PGPPATH/pubring.pgp          public key ring
$PGPPATH/secring.pgp          secret key ring
$PGPPATH/randseed.bin         random number seed file
/usr/local/lib/pgp/language.txt
$PGPPATH/language.txt         foreign language translation file
/usr/local/lib/pgp/pgp.hlp
$PGPPATH/pgp/pgp.hlp          online help text file
/usr/local/lib/pgp/pgpkey.hlp
$PGPPATH/pgp/pgpkey.hlp       online key-management help text file

NOTE

The manual is really good, and it’s really important in the long run that you read it. PGP may be an unpickable lock, but you have to put in in the door properly to keep out intruders. So read the manual and find out how!

CAVEATS

It is impossible to overemphasize the importance of protecting your secret key. Anyone gaining access to it can forge messages from you or read mail addressed to you. Be very cautious in using PGP on any multi-user unix system.

PGP is believed by its authors to be the most secure cryptographic software available to the public when used as directed, but then again everyone always claims their pet encryption system is secure. Read the section in the manual on "Trusting Snake Oil" and the section on "Vulnerabilities" for caveats.

DIAGNOSTICS

Mostly self explanatory.

BUGS

PGP was initially written for the PC, and behaves very PCish. In particular, its automagic file selection, file extensions, and the like all make it somewhat alien in the UNIX environment.

This man page needs to be updated to reflect all the latest features.

AUTHORS

Originally written by Philip R. Zimmermann. Later augmented by a cast of thousands.

LEGAL RESTRICTIONS

PGP 2.6.3i is freeware, and may be used for non-commercial purposes only. This version of PGP is illegal to use within the USA but is fine elsewhere in the world. US users should get a copy of MIT PGP 2.6.2 instead, or purchase the commercial version 2.7.1 from ViaCrypt.

For detailed information on PGP licensing, distribution, copyrights, patents, trademarks, liability limitations, and export controls, see the "Legal Issues" section in the "PGP User’s Guide, Volume II: Special Topics".

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