How to Decode Base64 to TLV in PHP-CodePudding

I am building an inhouse Invoicing solution for my company. The government requires us to create QR Code fields encoded in Tag-Length-Value (TLV) format.

The TLV encoding shall be as follows:

Tag: the tag value as mentioned above stored in one byte

Length: the length of the byte array resulted from the UTF8 encoding of the field value. The length shall be stored in one byte.

Value: the byte array resulting from the UTF8 encoding of the field value.

In the example they have provided this Base64 Output

AQkxMjM0NTY3ODkCCjEyLzEyLzIwMjADBDEwMDADAzE1MPaIn2Z2jg6VqWvWV6IrZZNzLF7xvZrWXW5xRV5yFY2xFu0ycXOiyqV0k7Wsh6b1IcE2Tfzap1AQAQVsktmsv1FFQ1MxIAAAAGKblFMh9nFRSn8tvftXqo9zRSz2VEAPITSZ3W7UDHKhUx 7yXGijLtJSZGXMOc jpKwARzDl68GmmRd75NWdOs=

When I decode using

$base64 = "AQkxMjM0NTY3ODkCCjEyLzEyLzIwMjADBDEwMDADAzE1MPaIn2Z2jg6VqWvWV6IrZZNzLF7xvZrWXW5xRV5yFY2xFu0ycXOiyqV0k7Wsh6b1IcE2Tfzap1AQAQVsktmsv1FFQ1MxIAAAAGKblFMh9nFRSn8tvftXqo9zRSz2VEAPITSZ3W7UDHKhUx 7yXGijLtJSZGXMOc jpKwARzDl68GmmRd75NWdOs=";
echo base64_decode($base64);

The response i get is:

    123456789
12/12/20201000150���fv���k�W� e�s,^��]nqE^r���2qs�ʥt������!�6M�ڧPl�٬�QECS1 b��S!�qQJ-��W��sE,�T@!4��n�r�S��q���II��0�>���×��d]�Vt�

Tag 1: Seller's Name

Tag 2: Vat Registration number

Tag 3: Timestamp of the invoice

Tag 4: Invoice Total

Tag 5: Tax Total

Tag 6: Hash of XML invoice

Tag 7: ECDSA Signature

Tag 8: ECDSA Public Key

Tag 9: ECDSA signature of the cryptographic stamp’s public key

What Am I doing wrong here and what is the right syntax to correct it?

CodePudding user response：

Knowing it's binary data, we can echo it with bin2hex(base64_decode($base64)), and see this:

0109313233343536373839020a31322f31322f323032300304313030300303313530f6889f66768e0e95a96bd657a22b6593732c5ef1bd9ad65d6e71455e72158db116ed327173a2caa57493b5ac87a6f521c1364dfcdaa7501001056c92d9acbf514543533120000000629b945321f671514a7f2dbdfb57aa8f73452cf654400f213499dd6ed40c72a1531fbbc971a28cbb4949919730e73e8e92b0011cc397af069a645def935674eb

For easier viewing, I used the command line tools base64 -d and xxd to get this view:

00000000: 0109 3132 3334 3536 3738 3902 0a31 322f  ..123456789..12/
00000010: 3132 2f32 3032 3003 0431 3030 3003 0331  12/2020..1000..1
00000020: 3530 f688 9f66 768e 0e95 a96b d657 a22b  50...fv....k.W. 
00000030: 6593 732c 5ef1 bd9a d65d 6e71 455e 7215  e.s,^....]nqE^r.
00000040: 8db1 16ed 3271 73a2 caa5 7493 b5ac 87a6  ....2qs...t.....
00000050: f521 c136 4dfc daa7 5010 0105 6c92 d9ac  .!.6M...P...l...
00000060: bf51 4543 5331 2000 0000 629b 9453 21f6  .QECS1 ...b..S!.
00000070: 7151 4a7f 2dbd fb57 aa8f 7345 2cf6 5440  qQJ.-..W..sE,.T@
00000080: 0f21 3499 dd6e d40c 72a1 531f bbc9 71a2  .!4..n..r.S...q.
00000090: 8cbb 4949 9197 30e7 3e8e 92b0 011c c397  ..II..0.>.......
000000a0: af06 9a64 5def 9356 74eb                 ...d]..Vt.

You haven't explained what the possible "tag" values are, but I can see the start of that string has a tag of 0x01, a length of 0x09, and the following 9 bytes are ASCII/UTF-8 for 123456789; it then has a tag of 0x02, a length of 0x0a, and the next 10 characters are ASCII/UTF-8 12/12/2020; and so on.

Later, there is a tag of f6 with a length of 88, and some binary data, but without knowing what tag f6 means, I've no reason to suppose that's a problem - maybe it embeds an image, or a stream of compressed data.

CodePudding user response：

Edited:

In the Security Specification it says:

4.2 Structure of the Cryptographic Stamp applied on the QR code The below specifications of the Cryptographic Stamp required for the QR code are based Annex (2) of the Controls, Requirements, Technical Specifications and Procedural Rules for Implementing the Provisions of the E-Invoicing Regulation. The QR code Cryptographic Stamp shall be generated use the same digital certificate used for stamping the electronic invoices. Please refer to section 3 for the requirements applicable to the management and use of digital certificates used to apply Cryptographic Stamp on electronic invoices. The Cryptographic Stamp shall be applied on the entire TLV encoding of the QR code fields (from tag 1 to tag 6) then it shall be appended to the TLV structure. The Cryptographic Stamp consists of two fields as shown in the below table:

I assume the part of the data is a part of the Cryptographic Stamp