gistfile1.php

<?php
// Signature Version 4 Key Derivation Samples in PHP5
// http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html
function hash_sha256_raw($msg, $key)
{
    return hash_hmac("sha256", $msg, $key, true);
}

function getSignature($key, $dateStamp, $regionName, $serviceName)
{
    $kDate = hash_sha256_raw($dateStamp, "AWS4$key");
    $kRegion = hash_sha256_raw($regionName, $kDate);
    $kService = hash_sha256_raw($serviceName, $kRegion);
    $kSigning = hash_sha256_raw("aws4_request", $kService);

    return $kSigning;
}

$key = 'wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY';
$dateStamp = '20120215';
$regionName = 'us-east-1';
$serviceName = 'iam';

$signature = getSignature($key, $dateStamp, $regionName, $serviceName);
echo bin2hex($signature);

最近のPHPコーディングスタンダード事情に疎く関数名とか変数名はcamel caseなのかどうか