Source/WebCore/loader/PrivateClickMeasurement.cpp

/*
 * Copyright (C) 2019 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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#include "config.h"
#include "PrivateClickMeasurement.h"

#include "Logging.h"
#include "RuntimeEnabledFeatures.h"
#include <wtf/Expected.h>
#include <wtf/RandomNumber.h>
#include <wtf/URL.h>
#include <wtf/text/StringBuilder.h>
#include <wtf/text/StringToIntegerConversion.h>
#include <wtf/text/StringView.h>

namespace WebCore {

static const char privateClickMeasurementTriggerAttributionPath[] = "/.well-known/private-click-measurement/trigger-attribution/";
static const char privateClickMeasurementTokenSignaturePath[] = "/.well-known/private-click-measurement/sign-unlinkable-token/";
static const char privateClickMeasurementTokenPublicKeyPath[] = "/.well-known/private-click-measurement/get-token-public-key/";
static const char privateClickMeasurementReportAttributionPath[] = "/.well-known/private-click-measurement/report-attribution/";
const size_t privateClickMeasurementAttributionTriggerDataPathSegmentSize = 2;
const size_t privateClickMeasurementPriorityPathSegmentSize = 2;

const Seconds PrivateClickMeasurement::maxAge()
{
    return 24_h * 7;
};

bool PrivateClickMeasurement::isValid() const
{
    return m_attributionTriggerData
        && m_attributionTriggerData.value().isValid()
        && m_sourceID.isValid()
        && !m_sourceSite.registrableDomain.isEmpty()
        && !m_destinationSite.registrableDomain.isEmpty()
        && (m_timesToSend.sourceEarliestTimeToSend || m_timesToSend.destinationEarliestTimeToSend);
}

Expected<PrivateClickMeasurement::AttributionTriggerData, String> PrivateClickMeasurement::parseAttributionRequest(const URL& redirectURL)
{
    auto path = StringView(redirectURL.string()).substring(redirectURL.pathStart(), redirectURL.pathEnd() - redirectURL.pathStart());
    if (path.isEmpty() || !path.startsWith(privateClickMeasurementTriggerAttributionPath))
        return makeUnexpected(nullString());

    if (!redirectURL.protocolIs("https") || redirectURL.hasCredentials() || redirectURL.hasQuery() || redirectURL.hasFragmentIdentifier())
        return makeUnexpected("[Private Click Measurement] Conversion was not accepted because the URL's protocol is not HTTPS or the URL contains one or more of username, password, query string, and fragment."_s);


    auto prefixLength = sizeof(privateClickMeasurementTriggerAttributionPath) - 1;
    if (path.length() == prefixLength + privateClickMeasurementAttributionTriggerDataPathSegmentSize) {
        auto attributionTriggerDataUInt64 = parseInteger<uint64_t>(path.substring(prefixLength, privateClickMeasurementAttributionTriggerDataPathSegmentSize));
        if (!attributionTriggerDataUInt64 || *attributionTriggerDataUInt64 > AttributionTriggerData::MaxEntropy)
            return makeUnexpected(makeString("[Private Click Measurement] Conversion was not accepted because the conversion data could not be parsed or was higher than the allowed maximum of "_s, AttributionTriggerData::MaxEntropy, "."_s));

        return AttributionTriggerData { static_cast<uint32_t>(*attributionTriggerDataUInt64), Priority { 0 } };
    }
    
    if (path.length() == prefixLength + privateClickMeasurementAttributionTriggerDataPathSegmentSize + 1 + privateClickMeasurementPriorityPathSegmentSize) {
        auto attributionTriggerDataUInt64 = parseInteger<uint64_t>(path.substring(prefixLength, privateClickMeasurementAttributionTriggerDataPathSegmentSize));
        if (!attributionTriggerDataUInt64 || *attributionTriggerDataUInt64 > AttributionTriggerData::MaxEntropy)
            return makeUnexpected(makeString("[Private Click Measurement] Conversion was not accepted because the conversion data could not be parsed or was higher than the allowed maximum of "_s, AttributionTriggerData::MaxEntropy, "."_s));

        auto attributionPriorityUInt64 = parseInteger<uint64_t>(path.substring(prefixLength + privateClickMeasurementAttributionTriggerDataPathSegmentSize + 1, privateClickMeasurementPriorityPathSegmentSize));
        if (!attributionPriorityUInt64 || *attributionPriorityUInt64 > Priority::MaxEntropy)
            return makeUnexpected(makeString("[Private Click Measurement] Conversion was not accepted because the priority could not be parsed or was higher than the allowed maximum of "_s, Priority::MaxEntropy, "."_s));

        return AttributionTriggerData { static_cast<uint32_t>(*attributionTriggerDataUInt64), Priority { static_cast<uint32_t>(*attributionPriorityUInt64) } };
    }

    return makeUnexpected("[Private Click Measurement] Conversion was not accepted because the URL path contained unrecognized parts."_s);
}

bool PrivateClickMeasurement::hasPreviouslyBeenReported()
{
    return !m_timesToSend.sourceEarliestTimeToSend || !m_timesToSend.destinationEarliestTimeToSend;
}

static Seconds randomlyBetweenTwentyFourAndFortyEightHours()
{
    return 24_h + Seconds(randomNumber() * (24_h).value());
}

PrivateClickMeasurement::AttributionSecondsUntilSendData PrivateClickMeasurement::attributeAndGetEarliestTimeToSend(AttributionTriggerData&& attributionTriggerData)
{
    if (!attributionTriggerData.isValid() || (m_attributionTriggerData && m_attributionTriggerData->priority >= attributionTriggerData.priority))
        return { };

    m_attributionTriggerData = WTFMove(attributionTriggerData);
    // 24-48 hour delay before sending. This helps privacy since the conversion and the attribution
    // requests are detached and the time of the attribution does not reveal the time of the conversion.
    auto sourceSecondsUntilSend = randomlyBetweenTwentyFourAndFortyEightHours();
    auto destinationSecondsUntilSend = randomlyBetweenTwentyFourAndFortyEightHours();
    m_timesToSend = { WallTime::now() + sourceSecondsUntilSend, WallTime::now() + destinationSecondsUntilSend };

    return AttributionSecondsUntilSendData { sourceSecondsUntilSend, destinationSecondsUntilSend };
}

bool PrivateClickMeasurement::hasHigherPriorityThan(const PrivateClickMeasurement& other) const
{
    if (!other.m_attributionTriggerData)
        return true;
    
    if (!m_attributionTriggerData)
        return false;

    return m_attributionTriggerData->priority > other.m_attributionTriggerData->priority;
}

static URL attributionReportURL(const RegistrableDomain& registrableDomain)
{
    StringBuilder builder;
    builder.appendLiteral("https://");
    builder.append(registrableDomain.string());
    builder.appendLiteral(privateClickMeasurementReportAttributionPath);

    URL url { URL(), builder.toString() };
    if (url.isValid())
        return url;

    return URL();
}

URL PrivateClickMeasurement::attributionReportSourceURL() const
{
    if (!isValid())
        return URL();

    return attributionReportURL(m_sourceSite.registrableDomain);
}

URL PrivateClickMeasurement::attributionReportAttributeOnURL() const
{
    if (!isValid())
        return URL();

    return attributionReportURL(m_destinationSite.registrableDomain);
}

Ref<JSON::Object> PrivateClickMeasurement::attributionReportJSON() const
{
    auto reportDetails = JSON::Object::create();
    if (!m_attributionTriggerData || !isValid())
        return reportDetails;

    reportDetails->setString("source_engagement_type"_s, "click"_s);
    reportDetails->setString("source_site"_s, m_sourceSite.registrableDomain.string());
    reportDetails->setInteger("source_id"_s, m_sourceID.id);
    reportDetails->setString("attributed_on_site"_s, m_destinationSite.registrableDomain.string());
    reportDetails->setInteger("trigger_data"_s, m_attributionTriggerData->data);
    reportDetails->setInteger("version"_s, 2);

    // This token has been kept secret this far and cannot be linked to the unlinkable token.
    if (m_sourceSecretToken) {
        reportDetails->setString("source_secret_token"_s, m_sourceSecretToken->tokenBase64URL);
        reportDetails->setString("source_secret_token_signature"_s, m_sourceSecretToken->signatureBase64URL);
    }

    return reportDetails;
}

// MARK: - Fraud Prevention

static constexpr uint32_t EphemeralSourceNonceRequiredNumberOfBytes = 16;

bool PrivateClickMeasurement::EphemeralSourceNonce::isValid() const
{
    // FIXME: Investigate if we can do with a simple length check instead of decoding.
    // https://bugs.webkit.org/show_bug.cgi?id=221945
    auto digest = base64URLDecode(nonce);
    if (!digest)
        return false;
    return digest->size() == EphemeralSourceNonceRequiredNumberOfBytes;
}

void PrivateClickMeasurement::setEphemeralSourceNonce(EphemeralSourceNonce&& nonce)
{
    if (!nonce.isValid())
        return;
    m_ephemeralSourceNonce = WTFMove(nonce);
}

URL PrivateClickMeasurement::tokenSignatureURL() const
{
    if (!m_ephemeralSourceNonce || !m_ephemeralSourceNonce->isValid())
        return URL();

    StringBuilder builder;
    builder.appendLiteral("https://");
    builder.append(m_sourceSite.registrableDomain.string());
    builder.appendLiteral(privateClickMeasurementTokenSignaturePath);

    URL url { URL(), builder.toString() };
    if (url.isValid())
        return url;

    return URL();
}

URL PrivateClickMeasurement::tokenPublicKeyURL() const
{
    StringBuilder builder;
    builder.appendLiteral("https://");
    builder.append(m_sourceSite.registrableDomain.string());
    builder.appendLiteral(privateClickMeasurementTokenPublicKeyPath);

    URL url { URL(), builder.toString() };
    if (url.isValid())
        return url;

    return URL();
}

Ref<JSON::Object> PrivateClickMeasurement::tokenSignatureJSON() const
{
    auto reportDetails = JSON::Object::create();
    if (!m_ephemeralSourceNonce || !m_ephemeralSourceNonce->isValid())
        return reportDetails;

    if (m_sourceUnlinkableToken.valueBase64URL.isEmpty())
        return reportDetails;

    reportDetails->setString("source_engagement_type"_s, "click"_s);
    reportDetails->setString("source_nonce"_s, m_ephemeralSourceNonce->nonce);
    // This token can not be linked to the secret token.
    reportDetails->setString("source_unlinkable_token"_s, m_sourceUnlinkableToken.valueBase64URL);
    reportDetails->setInteger("version"_s, 2);
    return reportDetails;
}

void PrivateClickMeasurement::setSourceSecretToken(SourceSecretToken&& token)
{
    if (!token.isValid())
        return;
    m_sourceSecretToken = WTFMove(token);
}

bool PrivateClickMeasurement::SourceSecretToken::isValid() const
{
    return !(tokenBase64URL.isEmpty() || signatureBase64URL.isEmpty() || keyIDBase64URL.isEmpty());
}

} // namespace WebCore