How to acquire Modulus and Exponent from existing RSA Public Key in PHP OpenSSL Library

Question

There are Private Key, Public Key, x509 Pem file. I want to acquire information about RSA Public Key from these files.

I can confirm it by the shell script as follows. $ openssl x509 -in cert.pem -text

...

    Subject Public Key Info:
        Public Key Algorithm: rsaEncryption
        RSA Public Key: (2048 bit)
            Modulus (2048 bit):
                00:e1:92:dc:05:84:c7:e1:2d:db:f3:48:84:90:32:
                ...
                da:7d:2f:95:d2:ab:28:6e:6c:be:0a:af:e0:cb:24:
                18:db
            Exponent: 65537 (0x10001)

...

Can I acquire a value of Modulus and Exponent in PHP OpenSSL library in the same way?

josemmo · Accepted Answer · 2017-08-29 12:09:36Z

8

You can try the following:

$key = file_get_contents("root/to/private_key.pem");
$data = openssl_pkey_get_private($key);
$data = openssl_pkey_get_details($data);

$key = $data['key'];
$modulus = $data['rsa']['n'];
$exponent = $data['rsa']['e'];

echo "Modulus: $modulus <br>Exponent: $exponent";

In case echoing $exponent shows nothing on screen, you can try var_dump($exponent) or var_dump($data) and you will see some strange chars.

edited Aug 29, 2017 at 12:09

josemmo

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answered Jan 4, 2015 at 7:04

Julio Eduardo

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user1469439 · Accepted Answer · 2012-07-31 13:58:33Z

Using phpseclib, a pure PHP X.509 implementation:

$x509 = new File_X509();
$cert = $x509->loadX509('-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----');

$pubkey = $x509->getPublicKey();
$parts = $pubkey->getPublicKey(CRYPT_RSA_PUBLIC_FORMAT_RAW);
echo $parts['e'] . "\r\n\r\n" . $parts['n'];

atomicinf · Accepted Answer · 2012-07-27 04:00:37Z

0

You probably want openssl_pkey_get_details($key).

This takes a key resource generated from openssl_pkey_get_private() or openssl_pkey_get_public() (?) and will return an array with keys bits, key, type, and a fourth key that is one of rsa, dsa, or dh depending on the key. The fourth key maps to another array with more details; for RSA keys, this subarray contains your modulus n and exponent e.

See this page and related pages in the PHP documentation for more usage notes.

(None of this is tested; let me know if this works for you!)

answered Jul 27, 2012 at 4:00

atomicinf

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