how to extract DER encoded certificate from base64 string

问题

Looking for help on how to decode the following base64 MerkleTreeLeaf string.

The MerkleTreeLeaf structure is a composite data structure that contains a timestamp as well as a digital certificate.

The structure is encoded as a Base64 encoded byte string. Within this byte string, there is an actual certificate encoded in DER format.

I am looking for a php solution to extract the DER encoded certificate.

Here is a sample of the base64 encoded string

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

If i use the online base64 convertors tool it shows some detail but obviously its unreadable. If I can extract the DER encoded certificate then I can use openssl to parse it.

回答1:

You can approach it the same way as the Python script in your comment, simply comparing the Python unpack documentation with the one for PHP. In case you only want the unparsed certificate, you can get away with

<?php

function mtl_to_x509($base64str) {
    $raw = base64_decode($base64str);
    // Parse the decoded string
    $cert_length = unpack('N', chr(0).substr($raw, 12, 3))[1];
    $cert_as_asn1 = substr($raw, 15, $cert_length);
    return $cert_as_asn1;
}

$example = "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";

print mtl_to_x509($example);

?>

To see that this does the job, note that we can indeed parse it with openssl:

$ php mtl_to_x509.php | openssl x509 -inform der -noout -text | grep Subject:
        Subject: 1.3.6.1.4.1.311.60.2.1.3=US/1.3.6.1.4.1.311.60.2.1.2=Delaware/1.3.6.1.4.1.311.60.2.1.1=Wilmington, C=US, ST=California, L=Mountain View/businessCategory=Private Organization/serialNumber=2158113, O=Symantec Corp, OU=for ct testing-- ecc, CN=evpro1.ev1.symantec.com

In case you end up needing the rest of the data structure as well, the relevant unpacking will look as follows:

$version = unpack('C', substr($raw, 0, 1))[1];
$ctype = unpack('C', substr($raw, 1, 1))[1];
$timestamp = unpack('J', substr($raw, 2, 8))[1];
$entry_type = unpack('n', substr($raw, 10, 2))[1];

来源：https://stackoverflow.com/questions/32686497/how-to-extract-der-encoded-certificate-from-base64-string

标签

php

encoding

certificate