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/*
* Copyright (C) 2025 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* 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
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "StringEntropyHelpers.h"
#include <array>
#include <wtf/text/MakeString.h>
namespace WebCore::StringEntropyHelpers {
enum class Symbol : uint8_t {
HexLower = 0,
NonHexLower,
HexUpper,
NonHexUpper,
Digit,
Dash,
Underscore,
FullStop,
OtherPunctuation,
OtherCharacter,
NumberOfSymbols // Must stay at the end.
};
static constexpr size_t numberOfSymbols = static_cast<size_t>(Symbol::NumberOfSymbols);
static Symbol symbol(UChar32 character)
{
if (character >= 'a' && character <= 'f')
return Symbol::HexLower;
if (character >= 'g' && character <= 'z')
return Symbol::NonHexLower;
if (character >= 'A' && character <= 'F')
return Symbol::HexUpper;
if (character >= 'G' && character <= 'Z')
return Symbol::NonHexUpper;
if (character >= '0' && character <= '9')
return Symbol::Digit;
switch (character) {
case '-':
return Symbol::Dash;
case '_':
return Symbol::Underscore;
case '.':
return Symbol::FullStop;
case '+':
case '=':
case '/':
case '\\':
return Symbol::OtherPunctuation;
default:
break;
}
return Symbol::OtherCharacter;
}
static constexpr std::array<uint8_t, numberOfSymbols * numberOfSymbols> quantizedBigramWeights { {
153, 214, 100, 97, 116, 180, 199, 179, 119, 121, // HexLower
209, 194, 86, 78, 106, 236, 203, 212, 123, 183, // NonHexLower
135, 125, 75, 93, 92, 124, 122, 121, 17, 173, // HexUpper
138, 100, 89, 80, 53, 145, 122, 117, 75, 114, // NonHexUpper
111, 99, 114, 53, 126, 139, 155, 152, 86, 157, // Digit
179, 235, 186, 185, 147, 144, 154, 164, 77, 156, // Dash
199, 194, 160, 154, 167, 162, 174, 112, 127, 112, // Underscore
173, 174, 210, 141, 162, 221, 104, 147, 167, 255, // FullStop
134, 153, 66, 72, 128, 88, 50, 127, 0, 114, // OtherPunctuation
158, 160, 112, 53, 167, 187, 131, 174, 182, 163, // OtherCharacter
} };
static double dequantize(uint8_t quantizedWeight)
{
static constexpr double weightScale = 0.0273696267;
static constexpr double weightZeroPoint = -4.0833584258;
return quantizedWeight * weightScale + weightZeroPoint;
}
static double bigramWeight(Symbol first, Symbol second)
{
auto tableOffset = numberOfSymbols * static_cast<uint8_t>(first) + static_cast<uint8_t>(second);
return dequantize(quantizedBigramWeights[tableOffset]);
}
static double entropyScore(StringView text)
{
auto textLength = text.length();
if (textLength <= 1)
return 0;
double totalWeight = 0;
std::optional<Symbol> previousSymbol;
for (size_t i = 0; i < textLength; ++i) {
auto character = text[i];
auto currentSymbol = symbol(character);
if (previousSymbol)
totalWeight += bigramWeight(*previousSymbol, currentSymbol);
previousSymbol = currentSymbol;
}
return totalWeight / textLength;
}
static bool isProbablyHumanReadable(StringView text, double entropyThreshold = 0)
{
static constexpr auto highEntropyThreshold = 40;
static constexpr auto lowEntropyThreshold = 5;
if (text.length() >= highEntropyThreshold)
return false;
if (text.length() <= lowEntropyThreshold)
return true;
return entropyScore(text) >= entropyThreshold;
}
String lowEntropyLastPathComponent(const URL& url, const String& fallbackName)
{
if (url.protocolIsData() || url.protocolIsBlob() || url.protocolIsJavaScript())
return fallbackName;
auto component = url.lastPathComponent();
if (isProbablyHumanReadable(component))
return component.toString();
auto fullStopIndex = component.reverseFind('.');
if (fullStopIndex == notFound)
return fallbackName;
return makeString(fallbackName, component.right(component.length() - fullStopIndex));
}
URL removeHighEntropyComponents(const URL& url)
{
if (url.protocolIs("mailto"_s) || url.protocolIs("tel"_s))
return url;
if (url.protocolIsData() || url.protocolIsBlob() || url.protocolIsJavaScript()) {
URL urlPreservingProtocolOnly;
urlPreservingProtocolOnly.setProtocol(url.protocol());
return urlPreservingProtocolOnly;
}
auto newURL = url;
StringBuilder newPath;
bool removedAnyPathComponent = false;
for (auto component : url.path().split('/')) {
if (!isProbablyHumanReadable(component)) {
removedAnyPathComponent = true;
continue;
}
if (!newPath.isEmpty())
newPath.append('/');
newPath.append(component);
}
if (removedAnyPathComponent)
newURL.setPath(newPath.toString());
newURL.removeQueryAndFragmentIdentifier();
return newURL;
}
} // namespace WebCore::StringEntropyHelpers
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