### Install PHPASN1 using Composer

Source: https://github.com/maajiko/epay/blob/main/includes/vendor/fgrosse/phpasn1/README.md

Use Composer to install the PHPASN1 library. This is the recommended installation method.

```bash
$ composer require fgrosse/phpasn1
```

--------------------------------

### Parsing Binary Data with a Template

Source: https://github.com/maajiko/epay/blob/main/includes/vendor/fgrosse/phpasn1/README.md

Use TemplateParser to parse binary data according to a predefined template structure. This method throws an exception if the data does not match the template.

```php
use FG\ASN1\TemplateParser;

// first define your template
$template = [
    Identifier::SEQUENCE => [
        Identifier::SET => [
            Identifier::OBJECT_IDENTIFIER,
            Identifier::SEQUENCE => [
                Identifier::INTEGER,
                Identifier::BITSTRING,
            ]
        ]
    ]
];

// if your binary data is not matching the template you provided this will throw an `\Exception`:
$parser = new TemplateParser();
$object = $parser->parseBinary($data, $template);

// there is also a convenience function if you parse binary data from base64:
$object = $parser->parseBase64($data, $template);
```

--------------------------------

### Encoding ASN.1 Structures

Source: https://github.com/maajiko/epay/blob/main/includes/vendor/fgrosse/phpasn1/README.md

Create and encode various ASN.1 universal types like Integer, Boolean, IA5String, ObjectIdentifier, Sequence, and Set. The data is encoded using DER encoding.

```php
use FG\ASN1\OID;
use FG\ASN1\Universal\Integer;
use FG\ASN1\Universal\Boolean;
use FG\ASN1\Universal\Enumerated;
use FG\ASN1\Universal\IA5String;
use FG\ASN1\Universal\ObjectIdentifier;
use FG\ASN1\Universal\PrintableString;
use FG\ASN1\Universal\Sequence;
use FG\ASN1\Universal\Set;
use FG\ASN1\Universal\NullObject;

$integer = new Integer(123456);
$boolean = new Boolean(true);
$enum = new Enumerated(1);
$ia5String = new IA5String('Hello world');

$asnNull = new NullObject();
$objectIdentifier1 = new ObjectIdentifier('1.2.250.1.16.9');
$objectIdentifier2 = new ObjectIdentifier(OID::RSA_ENCRYPTION);
$printableString = new PrintableString('Foo bar');

$sequence = new Sequence($integer, $boolean, $enum, $ia5String);
$set = new Set($sequence, $asnNull, $objectIdentifier1, $objectIdentifier2, $printableString);

$myBinary  = $sequence->getBinary();
$myBinary .= $set->getBinary();

echo base64_encode($myBinary);
```

--------------------------------

### Decoding BER Encoded Binary Data

Source: https://github.com/maajiko/epay/blob/main/includes/vendor/fgrosse/phpasn1/README.md

Decode BER encoded binary data into an ASNObject. Ensure the binary data is correctly decoded from its base64 representation before parsing.

```php
use FG\ASN1\ASNObject;

$base64String = ...
$binaryData = base64_decode($base64String);
$asnObject = ASNObject::fromBinary($binaryData);


// do stuff
```

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