CompressedData

One of the features the Cryptographic Message Syntax (CMS) provides is to act as a wrapper format for compressed files.

Note that this feature requires the zlib extension be installed (until such time that a shim can be written).

Reading CompressedData CMS

The method for loading a CompressedData CMS is the same as loading any other CMS type:

use phpseclib4\File\CMS;

$cms = CMS::load(file_get_contents('compressed.pem'));

print_r($cms);

^{(download compressed.pem)}

$cms, in this case, is a CMS\CompressedData object which, in turn, is basically a thin wrapper around an instance of \phpseclib4\File\ASN1\Constructed. Passing $cms through print_r() or var_dump() triggers the __debugInfo() magic method which, in turn, produces the following output:

contentType

phpseclib4\File\ASN1\Types\OID

id-ct-compressedData

content

version

phpseclib4\File\ASN1\Types\Integer

v0

compressionAlgorithm

algorithm

phpseclib4\File\ASN1\Types\OID

id-alg-zlibCompress

encapContentInfo

eContentType

phpseclib4\File\ASN1\Types\OID

id-data

eContent

phpseclib4\File\ASN1\Types\OctetString

...

Extracting file contents

The decompressed content can be extracted by calling $cms->getContent().

Creating CompressedData

use phpseclib4\File\CMS;

$cms = new CMS\CompressedData(file_get_contents('...'));
echo $cms;

Output Format

By default, CMS objects, when cast to a string, are converted to base64-encoded PEMs. To make it so that casting to a string produces a binary encoded DERs one need simply call CMS::enableBinaryOutput(). To go back to PEMs calling CMS::disableBinaryOutput() is sufficient.

You can also convert a CMS object to binary by doing $cms->toString(['binary' => true]).