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farble across all channels, unpredictably #7793

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farble across all channels, unpredictably #7793

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4 changes: 2 additions & 2 deletions browser/farbling/brave_offscreencanvas_farbling_browsertest.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -30,9 +30,9 @@ using brave_shields::ControlType;

const char kEmbeddedTestServerDirectory[] = "canvas";
const char kTitleScript[] = "domAutomationController.send(document.title);";
const char kExpectedImageDataHashFarblingBalanced[] = "83";
const char kExpectedImageDataHashFarblingBalanced[] = "107";
const char kExpectedImageDataHashFarblingOff[] = "0";
const char kExpectedImageDataHashFarblingMaximum[] = "83";
const char kExpectedImageDataHashFarblingMaximum[] = "107";

class BraveOffscreenCanvasFarblingBrowserTest : public InProcessBrowserTest {
public:
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6 changes: 3 additions & 3 deletions chromium_src/third_party/blink/renderer/core/execution_context/execution_context.cc
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Expand Up @@ -193,9 +193,6 @@ BraveSessionCache::PerturbPixelsInternal(
// dimensions are less than SIZE_T_MAX. (Width and height are each
// limited to 32,767 pixels.)
const size_t pixel_count = data_buffer->Width() * data_buffer->Height();
// choose which channel (R, G, or B) to perturb
const uint8_t* first_byte = reinterpret_cast<const uint8_t*>(domain_key_);
uint8_t channel = *first_byte % 3;
// calculate initial seed to find first pixel to perturb, based on session
// key, domain key, and canvas contents
crypto::HMAC h(crypto::HMAC::SHA256);
Expand All @@ -209,11 +206,14 @@ BraveSessionCache::PerturbPixelsInternal(
canvas_key, sizeof canvas_key));
uint64_t v = *reinterpret_cast<uint64_t*>(canvas_key);
uint64_t pixel_index;
// choose which channel (R, G, or B) to perturb
uint8_t channel;
// iterate through 32-byte canvas key and use each bit to determine how to
// perturb the current pixel
for (int i = 0; i < 32; i++) {
uint8_t bit = canvas_key[i];
for (int j = 8; j >= 0; j--) {
channel = v % 3;
pixel_index = 4 * (v % pixel_count) + channel;
pixels[pixel_index] = pixels[pixel_index] ^ (bit & 0x1);
bit = bit >> 1;
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2 changes: 1 addition & 1 deletion components/content_settings/renderer/brave_content_settings_agent_impl_browsertest.cc
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Expand Up @@ -53,7 +53,7 @@ const char kGetImageDataScript[] =
"domAutomationController.send(ctx.getImageData(0, 0, canvas.width, "
"canvas.height).data.reduce(adder));";

const int kExpectedImageDataHashFarblingBalanced = 83;
const int kExpectedImageDataHashFarblingBalanced = 107;
const int kExpectedImageDataHashFarblingOff = 0;
const int kExpectedImageDataHashFarblingMaximum =
kExpectedImageDataHashFarblingBalanced;
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