NAME

Convert::PEM - Read/write encrypted ASN.1 PEM files

SYNOPSIS

use Convert::PEM;
my $pem = Convert::PEM->new(
               Name => "DSA PRIVATE KEY",
               Macro => "DSAPrivateKey",
               ASN => qq(
                   DSAPrivateKey SEQUENCE {
                       version INTEGER,
                       p INTEGER,
                       q INTEGER,
                       g INTEGER,
                       pub_key INTEGER,
                       priv_key INTEGER
                   }
              ));

my $keyfile = 'private-key.pem';
my $pwd = 'foobar';

my $pkey = $pem->read(
               Filename => $keyfile,
               Password => $pwd
         );

$pem->write(
               Content  => $pkey,
               Password => $pwd,
               Filename => $keyfile
         );

DESCRIPTION

Convert::PEM reads and writes PEM files containing ASN.1-encoded objects. The files can optionally be encrypted using a symmetric cipher algorithm, such as 3DES. An unencrypted PEM file might look something like this:

-----BEGIN DH PARAMETERS-----
MB4CGQDUoLoCULb9LsYm5+/WN992xxbiLQlEuIsCAQM=
-----END DH PARAMETERS-----

The string beginning MB4C... is the Base64-encoded, ASN.1-encoded "object."

An encrypted file would have headers describing the type of encryption used, and the initialization vector:

-----BEGIN DH PARAMETERS-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,C814158661DC1449

AFAZFbnQNrGjZJ/ZemdVSoZa3HWujxZuvBHzHNoesxeyqqidFvnydA==
-----END DH PARAMETERS-----

The two headers (Proc-Type and DEK-Info) indicate information about the type of encryption used, and the string starting with AFAZ... is the Base64-encoded, encrypted, ASN.1-encoded contents of this "object."

The initialization vector (C814158661DC1449) is chosen randomly.

USAGE

$pem = Convert::PEM->new( %arg )

Constructs a new Convert::PEM object designed to read/write an object of a specific type (given in %arg, see below). Returns the new object on success, undef on failure (see ERROR HANDLING for details).

%arg can contain:

Name

The name of the object; when decoding a PEM-encoded stream, the name in the encoding will be checked against the value of Name. Similarly, when encoding an object, the value of Name will be used as the name of the object in the PEM-encoded content. For example, given the string FOO BAR, the output from encode will start with a header like:
```
-----BEGIN FOO BAR-----
```
Name is a required argument.
ASN

An ASN.1 description of the content to be either encoded or decoded.

ASN is an optional argument.
Macro

If your ASN.1 description (in the ASN parameter) includes more than one ASN.1 macro definition, you will want to use the Macro parameter to specify which definition to use when encoding/decoding objects. For example, if your ASN.1 description looks like this:
```
Foo ::= SEQUENCE {
    x INTEGER,
    bar Bar
}

Bar ::= INTEGER
```
If you want to encode/decode a Foo object, you will need to tell Convert::PEM to use the Foo macro definition by using the Macro parameter and setting the value to Foo.

Macro is an optional argument when an ASN.1 description is provided.
InForm

Specify what type of file to expect when using the read method. Value may be either PEM or DER. Default is "PEM".

If "DER" is specified, encryption options are ignored when using the read method and file is read as an unencrypted blob. This option does not affect the decode behavior.

InForm is an optional argument.
OutForm

Specify what type of file the write method should output. Value may be either PEM or DER. Default is "PEM".

If "DER" is specified, encryption options are ignored when using the write method and the file is written as an uncrypted blob. This option does not affect the encode behavior.

OutForm is an optional argument.

$obj = $pem->decode(%args)

Decodes, and, optionally, decrypts a PEM file, returning the object as decoded by Convert::ASN1. The difference between this method and read is that read reads the contents of a PEM file on disk; this method expects you to pass the PEM contents as an argument.

If an error occurs while reading the file or decrypting/decoding the contents, the function returns undef, and you should check the error message using the errstr method (below).

%args can contain:

Content

The PEM contents.
Password

The password with which the file contents were encrypted.

If the file is encrypted, this is a mandatory argument (well, it's not strictly mandatory, but decryption isn't going to work without it). Otherwise it's not necessary.

$blob = $pem->encode(%args)

Constructs the contents for the PEM file from an object: ASN.1-encodes the object, optionally encrypts those contents.

Returns undef on failure (encryption failure, file-writing failure, etc.); in this case you should check the error message using the errstr method (below). On success returns the constructed PEM string.

%args can contain:

Content

This method requires either Content or DER. An error will be generated if one of these arguments are not present.

A hash reference that will be passed to Convert::ASN1::encode, and which should correspond to the ASN.1 description you gave to the new method. The hash reference should have the exact same format as that returned from the read method.

This is required unless DER is specified.
DER

A string containing actual binary of the contents to be encoded. This bypasses ASN.1 encoding.

May be used in lieu of Content. If specified, will override Content.
Password

A password used to encrypt the contents of the PEM file. This is an optional argument; if not provided the contents will be unencrypted.
Cipher

The Cipher to use if a password is provided. This is an optional argument; if not provided, the default of DES-EDE3-CBC will be used or the cipher configured is $Convert::PEM::DefaultCipher. See below for a list of supported ciphers.

$obj = $pem->read(%args)

Reads, decodes, and, optionally, decrypts a PEM file, returning the object as decoded by Convert::ASN1 (or binary blob if ASN.1 description was not provided). This is implemented as a wrapper around decode, with the bonus of reading the PEM file from disk for you.

If an error occurs while reading the file or decrypting/decoding the contents, the function returns undef, and you should check the error message using the errstr method (below).

In addition to the arguments that can be passed to the decode method (minus the Content argument), %args can contain:

Filename

The location of the PEM file that you wish to read.
InForm

Specify what file type to read. Description can be found under new method. If specified, will override InForm provided in new method.

$pem->write(%args)

Constructs the contents for the PEM file from an object: ASN.1-encodes the object, optionally encrypts those contents; then writes the file to disk. This is implemented as a wrapper around encode, with the bonus of writing the file to disk for you.

In addition to the arguments for encode, %args can contain:

Filename

The location on disk where you'd like the PEM file written.
OutForm

Specify format to write out. Description can be found under new method. If specified, will override OutForm provided in new method.

$pem->from_der(%args)

Method used internally, but may be accessed directly decode an ASN.1 string into a perl structure object. If the Convert::PEM object has no ASN.1 definition, this method has no effect.

DER

Binary string to convert to an object.

This option is required.
Macro

If the object has an ASN definition, a Macro may be specified. If specified, it will override the object's Macro if one exists.

Macro is an optional argument.

$pem->to_der(%args)

Method used internally, but may be accessed directly to encode Content into binary data. If the Convert::PEM object has no ASN.1 definition, this method has no effect.

Content

An object to be ASN.1 encoded to a binary string.
Macro

If the object has an ASN definition, a Macro may be specified. If specified, it will override the object's Macro if one exists.

Macro is an optional argument.

$pem->errstr

Returns the value of the last error that occurred. This should only be considered meaningful when you've received undef from one of the functions above; in all other cases its relevance is undefined.

$pem->asn

Returns the Convert::ASN1 object used internally to decode and encode ASN.1 representations. This is useful when you wish to interact directly with that object; for example, if you need to call configure on that object to set the type of big-integer class to be used when decoding/encoding big integers:

$pem->asn->configure( decode => { bigint => 'Math::Pari' },
                      encode => { bigint => 'Math::Pari' } );

$pem->inform

Retruns the InForm configured for the object.

$pem->outform

Retruns the OutForm configured for the object.

$pem->cipher

Returns the Cipher configured for the object.

$pem->name

Returns the PEM Name of the object.

CONFIGURATION

To support any encryption/decryption, the appropriate cipher module needs to be installed.

Some settings may be viewed or configured through variables or methods.

Configuration settings are global to the package. If a setting is changed, it affects all Convert::PEM objects.

$Convert::PEM::DefaultCipher or $OBJ->DefaultCipher([NEW_CIPHER])

Used to configure a default cipher when writing to the disk. When using the method form $OBJ-DefaultCipher([NEW_CIPHER]) >, if NEW_CIPHER is not specified, will return the current setting. If the specified cipher is not recognized/valid, an error will be raised.

To list supported ciphers, use Convert::PEM::list_ciphers. Here is a list of supported Ciphers:

DES-CBC
DES-EDE3-CBC
AES-128-CBC
AES-192-CBC
AES-256-CBC
CAMELLIA-128-CBC
CAMELLIA-192-CBC
CAMELLIA-256-CBC
IDEA-CBC
SEED-CBC

Convert::PEM->has_cipher($cipher_name)

Will see if the cipher is supported and is configured with an encryption module.

Convert::PEM->has_cipher_module($cipher_name)

Will see if the cipher is supported and if the configured encryption module is usable. If it is not usable, will return undef. If it is usable, will return the name of the cipher module.

Convert::PEM->set_cipher_module($cipher,$module[,$all])

This function/method is used to specify a module name for a supported cipher. It accepts 2 or 3 arguments.

Convert::PEM->set_cipher_module(<cipher_name>, <module_name>[,0])
or
$OBJ->set_cipher_module(<cipher_name>, <module_name>[,0])

cipher_name

A supported cipher name. Use Convert::PEM::list_ciphers() to retrieve a list of supported ciphers.

module_name

A cipher module. The module must support the following methods:

$cipher_object = Cipher->new($key)
$cipher_object->encrypt($plaintext)
$cipher_object->decrypt($ciphertext)
$cipher_object->blocksize()

all

An optional boolean argument. If true will replace the modules for all supported ciphers matching the cipher being set. Default is true. If setting a cipher, only set this to false if it is desired to use a separate cipher for different key lengths of the same algorithm.

Convert::PEM->list_cipher_modules([$cipher_name])

If a cipher_name is provided, will return the module configured for the matching cipher name or undef if cipher is not supported. If cipher_name is not provided, will return a list of modules names configured as an array in array context or as a colon separated list in scalar context.

Here is a list of the cipher modules used by default.

Crypt::DES
Crypt::DES_EDE3
Crypt::Rijndael - AES-128-CBC, AES-192-CBC and AES-256-CBC
Crypt::Camellia - CAMELLIA-128-CBC, CAMELLIA-192-CBC and CAMELLIA-256-CBC
Crypt::IDEA
Crypt::SEED

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:

$pem->errstr

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

Convert::PEM->errstr

For example, if you try to decode an encrypted object, and you do not give a passphrase to decrypt the object:

my $obj = $pem->read( Filename => "encrypted.pem" )
    or die "Decryption failed: ", $pem->errstr;

LICENSE

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

AUTHOR & COPYRIGHTS

To install Convert::PEM, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Convert::PEM

CPAN shell

perl -MCPAN -e shell
install Convert::PEM

For more information on module installation, please visit the detailed CPAN module installation guide.

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