Crypt::OpenPGP - Pure-Perl OpenPGP implementation
my $pgp = Crypt::OpenPGP->new; my $signature = $pgp->sign( Filename => $file, KeyID => $key_id, Passphrase => $pass, Detach => 1, Armour => 1, ); my $valid = $pgp->verify( Signature => $signature, Files => [ $file ], ); my $ciphertext = $pgp->encrypt( Filename => $file, KeyID => $key_id, Armour => 1, ); my $plaintext = $pgp->decrypt( Data => $ciphertext, Passphrase => $pass, );
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, 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.
RSA
DSA
ElGamal
3DES
Blowfish
IDEA
Twofish
Rijndael
AES
128
192
256
MD5
SHA-1
RIPE-MD/160
ZIP
Zlib
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', KeyID => $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
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
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.
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.
undef
Constructs a new Crypt::OpenPGP instance and returns that object. Returns undef on failure.
%args can contain:
SecRing
Path to your secret keyring. If unspecified, Crypt::OpenPGP will look for your keyring in a number of default places.
PubRing
Path to your public keyring. If unspecified, Crypt::OpenPGP will look for your keyring in a number of default places.
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.
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 KeyID 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, Blowfish, IDEA, Twofish, Rijndael, Rijndael192, and Rijndael256 (the last two are Rijndael with key sizes of 192 and 256 bits, respectively).
DES3
Rijndael192
Rijndael256
This argument is optional; Crypt::OpenPGP currently defaults to DES3, but 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.
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 two-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. 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. 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).
No Signature
For example, to decrypt a message that may contain a signature that you want verified, you might use code like this:
my($pt, $validity) = $pgp->decrypt( ... ); die "Decryption failed: ", $pgp->errstr unless $pt; die "Signature verification failed: ", $pgp->errstr unless defined $validity || $pgp->errstr ne 'No Signature';
This checks for errors in decryption, as well as errors in signature verification, excluding the error denoting that the plaintext was not signed.
The ciphertext to be decrypted. This should be a simple scalar containing an arbitrary amount of data.
The path to a file to decrypt.
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 decrypt the ciphertext. 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.
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).
Creates and returns a digital signature on a block of data.
The text to be signed. This should be a simple scalar containing an arbitrary amount of data.
The path to a file to sign.
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.
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.
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.
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.
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.
SHA1
RIPEMD160
This argument is optional; by default 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.
3
4
The default value is 4, although this could change in the future.
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.
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).
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.
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.
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.
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 <foo@bar.com>
The Identity is used to build a User ID packet that is stored in each of the returned keyblocks.
String with which the secret key will be encrypted. When read in from disk, the key can then only be unlocked using this string.
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.
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;
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.
Crypt::OpenPGP is free software; you may redistribute it and/or modify it under the same terms as Perl itself.
Except where otherwise noted, Crypt::OpenPGP is Copyright 2001 Benjamin Trott, ben@rhumba.pair.com. All rights reserved.
To install Crypt::OpenPGP, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Crypt::OpenPGP
CPAN shell
perl -MCPAN -e shell install Crypt::OpenPGP
For more information on module installation, please visit the detailed CPAN module installation guide.