NAME
    Crypt::OpenPGP - Pure-Perl OpenPGP implementation

SYNOPSIS
        my $pgp = Crypt::OpenPGP->new;

        # Given an input stream (could be a signature, ciphertext, etc),
        # do the "right thing" to it.
        my $message_body; $message_body .= $_ while <STDIN>;
        my $result = $pgp->handle( Data => $message_body );

        # Create a detached, ASCII-armoured signature of $file using the
        # secret key $key_id, protected with the passphrase $pass. 
        my $file = 'really-from-me.txt';
        my $key_id = '...';
        my $pass = 'foo bar';
        my $signature = $pgp->sign(
            Filename   => $file,
            KeyID      => $key_id,
            Passphrase => $pass,
            Detach     => 1,
            Armour     => 1,
        );

        # Verify the detached signature $signature, which should be of the
        # source file $file.
        my $is_valid = $pgp->verify(
            Signature  => $signature,
            Files      => [ $file ],
        );

        # Using the public key associated with $key_id, encrypt the contents
        # of the file $file, and ASCII-armour the ciphertext.
        my $ciphertext = $pgp->encrypt(
            Filename   => $file,
            Recipients => $key_id,
            Armour     => 1,
        );

        # Decrypt $ciphertext using the secret key used to encrypt it,
        # which key is protected with the passphrase $pass.
        my $plaintext = $pgp->decrypt(
            Data       => $ciphertext,
            Passphrase => $pass,
        );

DESCRIPTION
    *Crypt::OpenPGP* is a pure-Perl implementation of the OpenPGP
    standard[1]. In addition to support for the standard itself,
    *Crypt::OpenPGP* claims compatibility with many other PGP
    implementations, both those that support the standard and those that
    preceded it.

    *Crypt::OpenPGP* provides signing/verification, encryption/decryption,
    keyring management, and key-pair generation; in short it should provide
    you with everything you need to PGP-enable yourself. Alternatively it
    can be used as part of a larger system; for example, perhaps you have a
    web-form-to-email generator written in Perl, and you'd like to encrypt
    outgoing messages, because they contain sensitive information.
    *Crypt::OpenPGP* can be plugged into such a scenario, given your public
    key, and told to encrypt all messages; they will then be readable only
    by you.

    This module currently supports "RSA" and "DSA" for digital signatures,
    and "RSA" and "ElGamal" for encryption/decryption. It supports the
    symmetric ciphers "3DES", "Blowfish", "IDEA", "Twofish", "CAST5", and
    "Rijndael" ("AES"). "Rijndael" is supported for key sizes of 128, 192,
    and 256 bits. *Crypt::OpenPGP* supports the digest algorithms "MD5",
    "SHA-1", and "RIPE-MD/160". And it supports "ZIP" and "Zlib"
    compression.

COMPATIBILITY
    One of the highest priorities for *Crypt::OpenPGP* is compatibility with
    other PGP implementations, including PGP implementations that existed
    before the OpenPGP standard.

    As a means towards that end, some of the high-level *Crypt::OpenPGP*
    methods can be used in compatibility mode; given an argument *Compat*
    and a PGP implementation with which they should be compatible, these
    method will do their best to choose ciphers, digest algorithms, etc.
    that are compatible with that implementation. For example, PGP2 only
    supports "IDEA" encryption, "MD5" digests, and version 3 signature
    formats; if you tell *Crypt::OpenPGP* that it must be compatible with
    PGP2, it will only use these algorithms/formats when encrypting and
    signing data.

    To use this feature, supply either *sign* or *encrypt* with the *Compat*
    parameter, giving it one of the values from the list below. For example:

        my $ct = $pgp->encrypt(
                      Compat     => 'PGP2',
                      Filename   => 'foo.pl',
                      Recipients => $key_id,
                 );

    Because *PGP2* was specified, the data will automatically be encrypted
    using the "IDEA" cipher, and will be compressed using "ZIP".

    Here is a list of the current compatibility sets and the algorithms and
    formats they support.

    *   PGP2

        Encryption: symmetric cipher = "IDEA", compression = "ZIP",
        modification detection code (MDC) = 0

        Signing: digest = "MD5", packet format = version 3

    *   PGP5

        Encryption: symmetric cipher = "3DES", compression = "ZIP",
        modification detection code (MDC) = 0

        Signing: digest = "SHA-1", packet format = version 3

    *   GnuPG

        Encryption: symmetric cipher = "Rijndael", compression = "Zlib",
        modification detection code (MDC) = 1

        Signing: digest = "RIPE-MD/160", packet format = version 4

    If the compatibility setting is unspecified (that is, if no *Compat*
    argument is supplied), the settings (ciphers, digests, etc.) fall back
    to their default settings.

USAGE
    *Crypt::OpenPGP* has the following high-level interface. On failure, all
    methods will return "undef" and set the *errstr* for the object; look
    below at the *ERROR HANDLING* section for more information.

  Crypt::OpenPGP->new( %args )
    Constructs a new *Crypt::OpenPGP* instance and returns that object.
    Returns "undef" on failure.

    *%args* can contain:

    *   Compat

        The compatibility mode for this *Crypt::OpenPGP* object. This value
        will propagate down into method calls upon this object, meaning that
        it will be applied for all method calls invoked on this object. For
        example, if you set *Compat* here, you do not have to set it again
        when calling *encrypt* or *sign* (below), unless, of course, you
        want to set *Compat* to a different value for those methods.

        *Compat* influences several factors upon object creation, unless
        otherwise overridden in the constructor arguments: if you have a
        configuration file for this compatibility mode (eg. ~/.gnupg/options
        for GnuPG), it will be automatically read in, and *Crypt::OpenPGP*
        will set any options relevant to its execution (symmetric cipher
        algorithm, etc.); *PubRing* and *SecRing* (below) are set according
        to the default values for this compatibility mode (eg.
        ~/.gnupg/pubring.gpg for the GnuPG public keyring).

    *   SecRing

        Path to your secret keyring. If unspecified, *Crypt::OpenPGP* will
        look for your keyring in a number of default places.

        As an alternative to passing in a path to the keyring file, you can
        pass in a *Crypt::OpenPGP::KeyRing* object representing a secret
        keyring.

    *   PubRing

        Path to your public keyring. If unspecified, *Crypt::OpenPGP* will
        look for your keyring in a number of default places.

        As an alternative to passing in a path to the keyring file, you can
        pass in a *Crypt::OpenPGP::KeyRing* object representing a public
        keyring.

    *   ConfigFile

        Path to a PGP/GnuPG config file. If specified, you must also pass in
        a value for the *Compat* parameter, stating what format config file
        you are passing in. For example, if you are passing in the path to a
        GnuPG config file, you should give a value of "GnuPG" for the
        *Compat* flag.

        If you leave *ConfigFile* unspecified, but you have specified a
        value for *Compat*, *Crypt::OpenPGP* will try to find your config
        file, based on the value of *Compat* that you pass in (eg.
        ~/.gnupg/options if *Compat* is "GnuPG").

        NOTE: if you do not specify a *Compat* flag, *Crypt::OpenPGP* cannot
        read any configuration files, even if you *have* specified a value
        for the *ConfigFile* parameter, because it will not be able to
        determine the proper config file format.

    *   KeyServer

        The hostname of the HKP keyserver. You can get a list of keyservers
        through

            % host -l pgp.net | grep wwwkeys

        If *AutoKeyRetrieve* is set to a true value, keys will be
        automatically retrieved from the keyserver if they are not found in
        your local keyring.

    *   AutoKeyRetrieve

        If set to a true value, and if *KeyServer* is set to a keyserver
        name, *encrypt* and *verify* will automatically try to fetch public
        keys from the keyserver if they are not found in your local keyring.

  $pgp->handle( %args )
    A do-what-I-mean wrapper around *decrypt* and *verify*. Given either a
    filename or a block of data--for example, data from an incoming email
    message--*handle* "handles" it as appropriate for whatever encryption or
    signing the message contains. For example, if the data is encrypted,
    *handle* will return the decrypted data (after prompting you for the
    passphrase). If the data is signed, *handle* will check the validity of
    the signature and return indication of the validity of the signature.

    The return value is a reference to a hash, which may contain the
    following keys, depending on the data passed to the method:

    *   Plaintext

        If the data is encrypted, the decrypted message.

    *   Validity

        If the data is signed, a true value if the signature is valid, a
        false value otherwise. The true value will be either the signer's
        email address, if available, or 1, if not.

    *   Signature

        If the data is signed, the *Crypt::OpenPGP::Signature* object
        representing the signature.

    If an error occurs, the return value will be "undef", and the error
    message can be obtained by calling *errstr* on the *Crypt::OpenPGP*
    object.

    *%args* can contain:

    *   Data

        The data to be "handled". This should be a simple scalar containing
        an arbitrary amount of data.

        *Data* is optional; if unspecified, you should specify a filename
        (see *Filename*, below).

    *   Filename

        The path to a file to "handle".

        *Filename* is optional; if unspecified, you should specify the data
        in *Data*, above. If both *Data* and *Filename* are specified, the
        data in *Data* overrides that in *Filename*.

    *   PassphraseCallback

        If the data is encrypted, you will need to supply *handle* with the
        proper passphrase to unlock the private key, or the password to
        decrypt the symmetrically-encrypted data (depending on the method of
        encryption used). If you do not specify this parameter, this default
        passphrase callback will be used:

            sub _default_passphrase_cb {
                my($cert) = @_;
                my $prompt;
                if ($cert) {
                    $prompt = sprintf qq(
            You need a passphrase to unlock the secret key for
            user "%s".
            %d-bit %s key, ID %s
    
            Enter passphrase: ), $cert->uid,
                                 $cert->key->size,
                                 $cert->key->alg,
                                 substr($cert->key_id_hex, -8, 8);
                } else {
                    $prompt = "Enter passphrase: ";
                }
                _prompt($prompt, '', 1);
            }

        If you do specify this parameter, make sure that your callback
        function can handle both asymmetric and symmetric encryption.

        See the *PassphraseCallback* parameter for *decrypt*, below.

  $pgp->encrypt( %args )
    Encrypts a block of data. The encryption is actually done with a
    symmetric cipher; the key for the symmetric cipher is then encrypted
    with either the public key of the recipient or using a passphrase that
    you enter. The former case is using public-key cryptography, the latter,
    standard symmetric ciphers. In the first case, the session key can only
    be unlocked by someone with the corresponding secret key; in the second,
    it can only be unlocked by someone who knows the passphrase.

    Given the parameter *SignKeyID* (see below), *encrypt* will first sign
    the message before encrypting it, adding a Signature packet to the
    encrypted plaintext.

    Returns a block of data containing two PGP packets: the encrypted
    symmetric key and the encrypted data.

    On failure returns "undef".

    *%args* can contain:

    *   Compat

        Specifies the PGP compatibility setting. See *COMPATIBILITY*, above.

    *   Data

        The plaintext to be encrypted. This should be a simple scalar
        containing an arbitrary amount of data.

        *Data* is optional; if unspecified, you should specify a filename
        (see *Filename*, below).

    *   Filename

        The path to a file to encrypt.

        *Filename* is optional; if unspecified, you should specify the data
        in *Data*, above. If both *Data* and *Filename* are specified, the
        data in *Data* overrides that in *Filename*.

    *   Recipients

        The intended recipients of the encrypted message. In other words,
        either the key IDs or user IDs of the public keys that should be
        used to encrypt the message. Each recipient specified should be
        either a key ID--an 8-digit or 16-digit hexadecimal number--or part
        of a user ID that can be used to look up the user's public key in
        your keyring. Examples:

            8-digit hex key ID: 123ABC45
            16-digit hex key ID: 678DEF90123ABC45
            (Part of) User ID: foo@bar

        Note that the 8-digit hex key ID is the last 8 digits of the (long)
        16-digit hex key ID.

        If you wish to encrypt the message for multiple recipients, the
        value of *Recipients* should be a reference to a list of recipients
        (as defined above). For each recipient in the list, the public key
        will be looked up in your public keyring, and an encrypted session
        key packet will be added to the encrypted message.

        This argument is optional; if not provided you should provide the
        *Passphrase* option (below) to perform symmetric-key encryption when
        encrypting the session key.

    *   KeyID

        A deprecated alias for *Recipients* (above). There is no need to use
        *KeyID*, as its functionality has been completely subsumed into the
        *Recipients* parameter.

    *   Passphrase

        The mechanism to use symmetric-key, or "conventional", encryption,
        when encrypting the session key. In other words, this allows you to
        use *Crypt::OpenPGP* for encryption/decryption without using
        public-key cryptography; this can be useful in certain circumstances
        (for example, when encrypting data locally on disk).

        This argument is optional; if not provided you should provide the
        *Recipients* option (above) to perform public-key encryption when
        encrypting the session key.

    *   RecipientsCallback

        After the list of recipients for a message (as given in
        *Recipients*, above) has been mapped into a set of keys from your
        public keyring, you can use *RecipientsCallback* to review/modify
        that list of keys. The value of *RecipientsCallback* should be a
        reference to a subroutine; when invoked that routine will be handed
        a reference to an array of *Crypt::OpenPGP::Certificate* objects. It
        should then return a reference to a list of such objects.

        This can be useful particularly when supplying user IDs in the list
        of *Recipients* for an encrypted message. Since user IDs are looked
        up using partial matches (eg. *b* could match *b*, *abc*, *bar*,
        etc.), one intended recipient may actually turn up multiple keys.
        You can use *RecipientsCallback* to audit that list before actually
        encrypting the message:

            my %BAD_KEYS = (
                ABCDEF1234567890 => 1,
                1234567890ABCDEF => 1,
            );
            my $cb = sub {
                my $keys = shift;
                my @return;
                for my $cert (@$keys) {
                    push @return, $cert unless $BAD_KEYS{ $cert->key_id_hex };
                }
                \@returns;
            };
            my $ct = $pgp->encrypt( ..., RecipientsCallback => $cb, ... );

    *   Cipher

        The name of a symmetric cipher with which the plaintext will be
        encrypted. Valid arguments are "DES3", "CAST5", "Blowfish", "IDEA",
        "Twofish", "Rijndael", "Rijndael192", and "Rijndael256" (the last
        two are "Rijndael" with key sizes of 192 and 256 bits,
        respectively).

        This argument is optional; if you have provided a *Compat*
        parameter, *Crypt::OpenPGP* will use the appropriate cipher for the
        supplied compatibility mode. Otherwise, *Crypt::OpenPGP* currently
        defaults to "DES3"; this could change in the future.

    *   Compress

        The name of a compression algorithm with which the plaintext will be
        compressed before it is encrypted. Valid values are "ZIP" and
        "Zlib".

        By default text is not compressed.

    *   Armour

        If true, the data returned from *encrypt* will be ASCII-armoured.
        This can be useful when you need to send data through email, for
        example.

        By default the returned data is not armoured.

    *   SignKeyID

        If you wish to sign the plaintext message before encrypting it,
        provide *encrypt* with the *SignKeyID* parameter and give it a key
        ID with which the message can be signed. This allows recipients of
        your message to verify its validity.

        By default messages not signed.

    *   SignPassphrase

        The passphrase to unlock the secret key to be used when signing the
        message.

        If you are signing the message--that is, if you have provided the
        *SignKeyID* parameter--either this argument or
        *SignPassphraseCallback* is required.

    *   SignPassphraseCallback

        The callback routine to enable the passphrase being passed in
        through some user-defined routine. See the *PassphraseCallback*
        parameter for *sign*, below.

        If you are signing the message--that is, if you have provided the
        *SignKeyID* parameter--either this argument or *SignPassphrase* is
        required.

    *   MDC

        When set to a true value, instructs *encrypt* to use encrypted MDC
        (modification detection code) packets instead of standard encrypted
        data packets. These are a newer form of encrypted data packets that
        are followed by a "SHA-1" hash of the plaintext data. This prevents
        attacks that modify the encrypted text by using a message digest to
        detect changes.

        By default *MDC* is set to 0, and *encrypt* generates standard
        encrypted data packets. Set it to a true value to turn on MDC
        packets. Note that *MDC* will automatically be turned on if you are
        using a *Compat* mode that is known to support it.

  $pgp->decrypt( %args )
    Decrypts a block of ciphertext. The ciphertext should be of the sort
    returned from *encrypt*, in either armoured or non-armoured form. This
    is compatible with all other implementations of PGP: the output of their
    encryption should serves as the input to this method.

    When called in scalar context, returns the plaintext (that is, the
    decrypted ciphertext), or "undef" on failure. When called in list
    context, returns a three-element list containing the plaintext and the
    result of signature verification (see next paragraph), or the empty list
    on failure. Either of the failure conditions listed here indicates that
    decryption failed.

    If *decrypt* is called in list context, and the encrypted text contains
    a signature over the plaintext, *decrypt* will attempt to verify the
    signature and will return the result of that verification as the second
    element in the return list, and the actual *Crypt::OpenPGP::Signature*
    object as the third element in the return list. If you call *decrypt* in
    list context and the ciphertext does *not* contain a signature, that
    second element will be "undef", and the *errstr* will be set to the
    string "No Signature\n". The second element in the return list can have
    one of three possible values: "undef", meaning that either an error
    occurred in verifying the signature, *or* the ciphertext did not contain
    a signature; 0, meaning that the signature is invalid; or a true value
    of either the signer's user ID or 1, if the user ID cannot be
    determined. Note that these are the same values returned from *verify*
    (below).

    For example, to decrypt a message that may contain a signature that you
    want verified, you might use code like this:

        my($pt, $valid, $sig) = $pgp->decrypt( ... );
        die "Decryption failed: ", $pgp->errstr unless $pt;
        die "Signature verification failed: ", $pgp->errstr
            unless defined $valid || $pgp->errstr !~ /^No Signature/;
        print "Signature created at ", $sig->timestamp, "\n";

    This checks for errors in decryption, as well as errors in signature
    verification, excluding the error denoting that the plaintext was not
    signed.

    *%args* can contain:

    *   Data

        The ciphertext to be decrypted. This should be a simple scalar
        containing an arbitrary amount of data.

        *Data* is optional; if unspecified, you should specify a filename
        (see *Filename*, below).

    *   Filename

        The path to a file to decrypt.

        *Filename* is optional; if unspecified, you should specify the data
        in *Data*, above. If both *Data* and *Filename* are specified, the
        data in *Data* overrides that in *Filename*.

    *   Passphrase

        The passphrase to unlock your secret key, or to decrypt a
        symmetrically-encrypted message; the usage depends on how the
        message is encrypted.

        This argument is optional if your secret key is protected; if not
        provided you should supply the *PassphraseCallback* parameter
        (below).

    *   PassphraseCallback

        A callback routine to allow interactive users (for example) to enter
        the passphrase for the specific key being used to decrypt the
        ciphertext, or the passphrase used to encrypt a
        symmetrically-encrypted message. This is useful when your ciphertext
        is encrypted to several recipients, if you do not necessarily know
        ahead of time the secret key that will be used to decrypt it. It is
        also useful when you wish to provide an interactive user with some
        feedback about the key being used to decrypt the message, or when
        you don't know what type of encryption (symmetric or public-key)
        will be used to encrypt a message.

        The value of this parameter should be a reference to a subroutine.
        This routine will be called when a passphrase is needed from the
        user, and it will be given either zero arguments or one argument,
        depending on whether the message is encrypted symmetrically (zero
        arguments) or using public-key encryption (one argument). If the
        latter, the one argument is a *Crypt::OpenPGP::Certificate* object
        representing the secret key. You can use the information in this
        object to present details about the key to the user.

        In either case, the callback routine should return the passphrase, a
        scalar string.

        Your callback routine can use the number of arguments to determine
        how to prompt the user for a passphrase; for example:

            sub passphrase_cb {
                if (my $cert = $_[0]) {
                    printf "Enter passphrase for secret key %s: ",
                        $cert->key_id_hex;
                } else {
                    print "Enter passphrase: ";
                }
            }

        This argument is optional if your secret key is protected; if not
        provided you should supply the *Passphrase* parameter (above).

  $pgp->sign( %args )
    Creates and returns a digital signature on a block of data.

    On failure returns "undef".

    *%args* can contain:

    *   Compat

        Specifies the PGP compatibility setting. See *COMPATIBILITY*, above.

    *   Data

        The text to be signed. This should be a simple scalar containing an
        arbitrary amount of data.

        *Data* is optional; if unspecified, you should specify a filename
        (see *Filename*, below).

    *   Filename

        The path to a file to sign.

        *Filename* is optional; if unspecified, you should specify the data
        in *Data*, above. If both *Data* and *Filename* are specified, the
        data in *Data* overrides that in *Filename*.

    *   Detach

        If set to a true value the signature created will be a detached
        signature; that is, a signature that does not contain the original
        text. This assumes that the person who will be verifying the
        signature can somehow obtain the original text (for example, if you
        sign the text of an email message, the original text is the
        message).

        By default signatures are not detached.

    *   Armour

        If true, the data returned from *sign* will be ASCII-armoured. This
        can be useful when you need to send data through email, for example.

        By default the returned signature is not armoured.

    *   Clearsign

        If true, the signature created on the data is a clear-text
        signature. This form of signature displays the clear text of the
        signed data, followed by the ASCII-armoured signature on that data.
        Such a format is desirable when sending signed messages to groups of
        users who may or may not have PGP, because it allows the text of the
        message to be readable without special software.

        When *Clearsign* is set to true, *Armour* and *Detach* are
        automatically turned on, because the signature created is a
        detached, armoured signature.

        By default *Clearsign* is false.

    *   KeyID

        The ID of the secret key that should be used to sign the message.
        The value of the key ID should be specified as a 16-digit
        hexadecimal number.

        This argument is mandatory.

    *   Passphrase

        The passphrase to unlock your secret key.

        This argument is optional if your secret key is protected; if not
        provided you should supply the *PassphraseCallback* parameter
        (below).

    *   PassphraseCallback

        A callback routine to allow interactive users (for example) to enter
        the passphrase for the specific key being used to sign the message.
        This is useful when you wish to provide an interactive user with
        some feedback about the key being used to sign the message.

        The value of this parameter should be a reference to a subroutine.
        This routine will be called when a passphrase is needed from the
        user, and it will be given one argument: a
        *Crypt::OpenPGP::Certificate* object representing the secret key.
        You can use the information in this object to present details about
        the key to the user. The callback routine should return the
        passphrase, a scalar string.

        This argument is optional if your secret key is protected; if not
        provided you should supply the *Passphrase* parameter (above).

    *   Digest

        The digest algorithm to use when creating the signature; the data to
        be signed is hashed by a message digest algorithm, then signed.
        Possible values are "MD5", "SHA1", and "RIPEMD160".

        This argument is optional; if not provided, the digest algorithm
        will be set based on the *Compat* setting provided to *sign* or
        *new*. If you have not provided a *Compat* setting, *SHA1* will be
        used.

    *   Version

        The format version of the created signature. The two possible values
        are 3 and 4; version 4 signatures will not be compatible with older
        PGP implementations.

        The default value is 4, although this could change in the future.

  $pgp->verify( %args )
    Verifies a digital signature. Returns true for a valid signature, 0 for
    an invalid signature, and "undef" if an error occurs (in which case you
    should call *errstr* to determine the source of the error). The 'true'
    value returned for a successful signature will be, if available, the PGP
    User ID of the person who created the signature. If that value is
    unavailable, the return value will be 1.

    If called in list context, the second element returned in the return
    list will be the *Crypt::OpenPGP::Signature* object representing the
    actual signature.

    *%args* can contain:

    *   Signature

        The signature data, as returned from *sign*. This data can be either
        a detached signature or a non-detached signature. If the former, you
        will need to specify the list of files comprising the original
        signed data (see *Data* or *Files*, below).

        Either this argument or *SigFile* is required.

    *   SigFile

        The path to a file containing the signature data. This data can be
        either a detached signature or a non-detached signature. If the
        former, you will need to specify the list of files comprising the
        original signed data (see *Data* or *Files*, below).

        Either this argument or *SigFile* is required.

    *   Data

        Specifies the original signed data.

        If the signature (in either *Signature* or *SigFile*) is a detached
        signature, either *Data* or *Files* is a mandatory argument.

    *   Files

        Specifies a list of files comprising the original signed data. The
        value should be a reference to a list of file paths; if there is
        only one file, the value can be specified as a scalar string, rather
        than a reference to a list.

        If the signature (in either *Signature* or *SigFile*) is a detached
        signature, either *Data* or *Files* is a mandatory argument.

  $pgp->keygen( %args )
    NOTE: this interface is alpha and could change in future releases!

    Generates a public/secret PGP keypair. Returns two keyblocks (objects of
    type *Crypt::OpenPGP::KeyBlock*), a public and a secret keyblock,
    respectively. A keyblock is essentially a block of keys, subkeys,
    signatures, and user ID PGP packets.

    *%args* can contain:

    *   Type

        The type of key to generate. Currently there are two valid values:
        "RSA" and "DSA". "ElGamal" key generation is not supported at the
        moment.

        This is a required argument.

    *   Size

        Bitsize of the key to be generated. This should be an even integer;
        there is no low end currently implemented in *Crypt::OpenPGP*, but
        for the sake of security *Size* should be at least 1024 bits.

        This is a required argument.

    *   Identity

        A string that identifies the owner of the key. Typically this is the
        combination of the user's name and an email address; for example,

            Foo Bar <[email protected]>

        The *Identity* is used to build a User ID packet that is stored in
        each of the returned keyblocks.

        This is a required argument.

    *   Passphrase

        String with which the secret key will be encrypted. When read in
        from disk, the key can then only be unlocked using this string.

        This is a required argument.

    *   Version

        Specifies the key version; defaults to version 4 keys. You should
        only set this to version 3 if you know why you are doing so (for
        backwards compatibility, most likely). Version 3 keys only support
        RSA.

    *   Verbosity

        Set to a true value to enable a status display during key
        generation; since key generation is a relatively lengthy process, it
        is helpful to have an indication that some action is occurring.

        *Verbosity* is 0 by default.

ERROR HANDLING
    If an error occurs in any of the above methods, the method will return
    "undef". You should then call the method *errstr* to determine the
    source of the error:

        $pgp->errstr

    In the case that you do not yet have a *Crypt::OpenPGP* object (that is,
    if an error occurs while creating a *Crypt::OpenPGP* object), the error
    can be obtained as a class method:

        Crypt::OpenPGP->errstr

    For example, if you try to decrypt some encrypted text, and you do not
    give a passphrase to unlock your secret key:

        my $pt = $pgp->decrypt( Filename => "encrypted_data" )
            or die "Decryption failed: ", $pgp->errstr;

SAMPLES/TUTORIALS
    Take a look at bin/pgplet for an example of usage of *Crypt::OpenPGP*.
    It gives you an example of using the four main major methods (*encrypt*,
    *sign*, *decrypt*, and *verify*), as well as the various parameters to
    those methods. It also demonstrates usage of the callback parameters
    (eg. *PassphraseCallback*).

    bin/pgplet currently does not have any documentation, but its interface
    mirrors that of *gpg*.

LICENSE
    Crypt::OpenPGP is free software; you may redistribute it and/or modify
    it under the same terms as Perl itself.

AUTHOR & COPYRIGHT
    Except where otherwise noted, Crypt::OpenPGP is Copyright 2001 Benjamin
    Trott, [email protected]. All rights reserved.

REFERENCES
    1 RFC4880 - OpenPGP Message Format (2007).
    http://www.faqs.org/rfcs/rfc4880.html