dir/include/crypto.php

<?php

require_once('library/ASNValue.class.php');
require_once('library/asn1.php');


function rsa_sign($data,$key) {

	$sig = '';
	if (version_compare(PHP_VERSION, '5.3.0', '>=')) {
		openssl_sign($data,$sig,$key,'sha256');
    }
    else {
		if(strlen($key) < 1024 || extension_loaded('gmp')) {
			require_once('library/phpsec/Crypt/RSA.php');
			$rsa = new CRYPT_RSA();
			$rsa->signatureMode = CRYPT_RSA_SIGNATURE_PKCS1;
			$rsa->setHash('sha256');
			$rsa->loadKey($key);
			$sig = $rsa->sign($data);
		}
		else {
			logger('rsa_sign: insecure algorithm used. Please upgrade PHP to 5.3');
			openssl_private_encrypt(hex2bin('3031300d060960864801650304020105000420') . hash('sha256',$data,true), $sig, $key);
		}
	}
	return $sig;
}

function rsa_verify($data,$sig,$key) {

	if (version_compare(PHP_VERSION, '5.3.0', '>=')) {
		$verify = openssl_verify($data,$sig,$key,'sha256');
    }
    else {
		if(strlen($key) <= 300 || extension_loaded('gmp')) {
			require_once('library/phpsec/Crypt/RSA.php');
			$rsa = new CRYPT_RSA();
			$rsa->signatureMode = CRYPT_RSA_SIGNATURE_PKCS1;
			$rsa->setHash('sha256');
			$rsa->loadKey($key);
			$verify = $rsa->verify($data,$sig);
		}
		else {
			// fallback sha256 verify for PHP < 5.3 and large key lengths
			$rawsig = '';
        	openssl_public_decrypt($sig,$rawsig,$key);
	        $verify = (($rawsig && substr($rawsig,-32) === hash('sha256',$data,true)) ? true : false);
    	}
	}
	return $verify;
}


function DerToPem($Der, $Private=false)
{
    //Encode:
    $Der = base64_encode($Der);
    //Split lines:
    $lines = str_split($Der, 65);
    $body = implode("\n", $lines);
    //Get title:
    $title = $Private? 'RSA PRIVATE KEY' : 'PUBLIC KEY';
    //Add wrapping:
    $result = "-----BEGIN {$title}-----\n";
    $result .= $body . "\n";
    $result .= "-----END {$title}-----\n";
 
    return $result;
}

function DerToRsa($Der)
{
    //Encode:
    $Der = base64_encode($Der);
    //Split lines:
    $lines = str_split($Der, 65);
    $body = implode("\n", $lines);
    //Get title:
    $title = 'RSA PUBLIC KEY';
    //Add wrapping:
    $result = "-----BEGIN {$title}-----\n";
    $result .= $body . "\n";
    $result .= "-----END {$title}-----\n";
 
    return $result;
}


function pkcs8_encode($Modulus,$PublicExponent) {
	//Encode key sequence
	$modulus = new ASNValue(ASNValue::TAG_INTEGER);
	$modulus->SetIntBuffer($Modulus);
	$publicExponent = new ASNValue(ASNValue::TAG_INTEGER);
	$publicExponent->SetIntBuffer($PublicExponent);
	$keySequenceItems = array($modulus, $publicExponent);
	$keySequence = new ASNValue(ASNValue::TAG_SEQUENCE);
	$keySequence->SetSequence($keySequenceItems);
	//Encode bit string
	$bitStringValue = $keySequence->Encode();
	$bitStringValue = chr(0x00) . $bitStringValue; //Add unused bits byte
	$bitString = new ASNValue(ASNValue::TAG_BITSTRING);
	$bitString->Value = $bitStringValue;
	//Encode body
	$bodyValue = "\x30\x0d\x06\x09\x2a\x86\x48\x86\xf7\x0d\x01\x01\x01\x05\x00" . $bitString->Encode();
	$body = new ASNValue(ASNValue::TAG_SEQUENCE);
	$body->Value = $bodyValue;
	//Get DER encoded public key:
	$PublicDER = $body->Encode();
	return $PublicDER;
}


function pkcs1_encode($Modulus,$PublicExponent) {
	//Encode key sequence
	$modulus = new ASNValue(ASNValue::TAG_INTEGER);
	$modulus->SetIntBuffer($Modulus);
	$publicExponent = new ASNValue(ASNValue::TAG_INTEGER);
	$publicExponent->SetIntBuffer($PublicExponent);
	$keySequenceItems = array($modulus, $publicExponent);
	$keySequence = new ASNValue(ASNValue::TAG_SEQUENCE);
	$keySequence->SetSequence($keySequenceItems);
	//Encode bit string
	$bitStringValue = $keySequence->Encode();
	return $bitStringValue;
}


function metopem($m,$e) {
	$der = pkcs8_encode($m,$e);
	$key = DerToPem($der,false);
	return $key;
}	


function pubrsatome($key,&$m,&$e) {
	require_once('library/asn1.php');
	require_once('include/salmon.php');

	$lines = explode("\n",$key);
	unset($lines[0]);
	unset($lines[count($lines)]);
	$x = base64_decode(implode('',$lines));

	$r = ASN_BASE::parseASNString($x);

	$m = base64url_decode($r[0]->asnData[0]->asnData);
	$e = base64url_decode($r[0]->asnData[1]->asnData);
}


function rsatopem($key) {
	pubrsatome($key,$m,$e);
	return(metopem($m,$e));
}

function pemtorsa($key) {
	pemtome($key,$m,$e);
	return(metorsa($m,$e));
}

function pemtome($key,&$m,&$e) {
	require_once('include/salmon.php');
	$lines = explode("\n",$key);
	unset($lines[0]);
	unset($lines[count($lines)]);
	$x = base64_decode(implode('',$lines));

	$r = ASN_BASE::parseASNString($x);

	$m = base64url_decode($r[0]->asnData[1]->asnData[0]->asnData[0]->asnData);
	$e = base64url_decode($r[0]->asnData[1]->asnData[0]->asnData[1]->asnData);
}

function metorsa($m,$e) {
	$der = pkcs1_encode($m,$e);
	$key = DerToRsa($der);
	return $key;
}	

function salmon_key($pubkey) {
	pemtome($pubkey,$m,$e);
	return 'RSA' . '.' . base64url_encode($m,true) . '.' . base64url_encode($e,true) ;
}