Need help understanding php signature verification

Question

I am trying to verify a signature in php, and have exhausted myself trying every example I have found on the net. I've gone round in circles so much I have probably missed the solution now.

So I have test data which is

$msg = "test data";

which produced this signature using the private key from my key pair

$signature = "avALtk00btVyV74e5UdXJ/VClVV/fsuoLZpXQjiCrkVijsmMZsYWZujN56+Aa2CEQYkomDsm9CJ/Tue7lNP0tYVZz9Y0RngpcV9VT9V3i+3rbvbBEnuJuS/5e+PR7kQGMh8rVuCtHpAJhSePMyipC3kM90EQJ0jyY3rFaHDNpSzVBpOnRYLzqbsdy45v0bN78A2J/HaIhJy87Sh4X1a+WMg9PLkqSSYZnRYOB8XVDCYfyeeekcvI4rvP51wBQcaLwu7S0xPQA8yHfJqMXCqdmBVUQZrk/X+CujdXUyJItDWA8j2N8AHmcAD5oRaJ6bX3zCQFM1QnKMi1ETLudzIqfA==";

and this is the public key from the signing key pair

$key = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAxv4nCiH4vXvSLsvlceCOk3yfH1EQgNqNaVGdnFxdw9IIjSVZvTVH45NCodCJ0GlHoDwQM7DMV1+QrtF91cn44xg4Ys9zr1xkaT4jWBTe3YKoTqJoLHR4UU03F6Y1jTELhjY2a2Kt0ijyvAOKM4bm3gCItfMx59ETGInz7Oubb1T4IJ8TuWmZsh+X57c6fgv0B2+eTr/5FMK2VxXV5tHkB9UNLBgnbw0IZuC6izF4OFk9hxgh96i5wCf2HhHaNoEryx7ZV2ZG9a0OQnYZ+x1zaOIw6dJkV7rip3H57ksQfoQWM0GKMBB7cWIgWsf/GlbYTVgw26MvzEzGPb9uCfx8rwIDAQAB";

I have tried wrapping the key with this

$pubkey = "-----BEGIN RSA PUBLIC KEY-----" . $key . "-----END RSA PUBLIC KEY-----";

and with this

$pubkey = "-----BEGIN PUBLIC KEY-----" . $key . "-----END PUBLIC KEY-----";

I have tried creating a public key id with both wrappings and without any wrapping, like this

$pubkeyid = openssl_pkey_get_public($pubkey);
$pubkeyid = openssl_pkey_get_public($key);

and I have tried verifying the signature with $key and $pubkeyid, with various algorithms and with none, like this

openssl_verify($msg, base64_decode($signature), $pubkeyid);
openssl_verify($msg, base64_decode($signature), $key);
openssl_verify($msg, base64_decode($signature), $pubkeyid, "sha256withRSAEncryption");
openssl_verify($msg, base64_decode($signature), $key, "sha256withRSAEncryption");
openssl_verify($msg, base64_decode($signature), $pubkeyid, OPENSSL_ALGO_SHA256);
openssl_verify($msg, base64_decode($signature), $key, OPENSSL_ALGO_SHA256);

I probably tried some other permutations, but can't remember now. My head hurts.

No matter what I tried, I have not managed to verify the signature. I can verify the signature using the public key in java easily.

I loathe asking for a working php example because I have tried so many I have already found on the net and just can't get them to work. Unfortunately phpseclib is not an option for me, so I have to use openssl.

Where am I going wrong?

Answer 1

Thanks to @miken32 I have now finally fixed the code. Turns out all I was missing was a couple of line breaks when formatting the PEM key. So the final, and very simple code is:

// Get base64 encoded public key.
// NOTE: this is just for testing the code, final production code stores the public key in a db.
$pubkey = $_POST['pubkey'];

// Convert pubkey in to PEM format (don't forget the line breaks).
$pubkey_pem = "-----BEGIN PUBLIC KEY-----\n$pubkey\n-----END PUBLIC KEY-----";

// Get public key.
$key = openssl_pkey_get_public($pubkey_pem);

if ($key == 0)
{
    $result = "Bad key zero.";
}
elseif ($key == false)
{
    $result = "Bad key false.";
}
else
{
    // Verify signature (use the same algorithm used to sign the msg).
    $result = openssl_verify($msg, base64_decode($signature), $key, OPENSSL_ALGO_SHA256);

    if ($result == 1)
    {
        $result = "Verified";
    }
    elseif ($result == 0)
    {
        $result = "Unverified";
    }
    else
    {
        $result = "Unknown verification response";
    }

}

// do something with the result.