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fix: fetch channel number dynamically. (3 or 4) #22

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fix: fetch channel number dynamically. (3 or 4) #22

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11 changes: 7 additions & 4 deletions Invoke-PSImage.ps1
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Original file line number Diff line number Diff line change
Expand Up @@ -120,8 +120,11 @@ PS>Invoke-PSImage -Script .\Invoke-Mimikatz.ps1 -Out .\evil-kiwi.png -Image .\ki
$randstr = [System.Web.Security.Membership]::GeneratePassword(128,0)
$randb = [system.Text.Encoding]::ASCII.GetBytes($randstr)

# channel Number: RGBA = 4, RGB = 3
$channelNum = [Math]::Abs($bmpData.Stride) / $img.Width;

# loop through the RGB array and copy the payload into it
for ($counter = 0; $counter -lt ($rgbValues.Length)/3; $counter++) {
for ($counter = 0; $counter -lt ($rgbValues.Length)/$channelNum; $counter++) {
if ($counter -lt $payload.Length){
$paybyte1 = [math]::Floor($payload[$counter]/16)
$paybyte2 = ($payload[$counter] -band 0x0f)
Expand All @@ -131,9 +134,9 @@ PS>Invoke-PSImage -Script .\Invoke-Mimikatz.ps1 -Out .\evil-kiwi.png -Image .\ki
$paybyte2 = ($randb[($counter+1)%67] -band 0x0f)
$paybyte3 = ($randb[($counter+2)%109] -band 0x0f)
}
$rgbValues[($counter*3)] = ($rgbValues[($counter*3)] -band 0xf0) -bor $paybyte1
$rgbValues[($counter*3+1)] = ($rgbValues[($counter*3+1)] -band 0xf0) -bor $paybyte2
$rgbValues[($counter*3+2)] = ($rgbValues[($counter*3+2)] -band 0xf0) -bor $paybyte3
$rgbValues[($counter*$channelNum)] = ($rgbValues[($counter*$channelNum)] -band 0xf0) -bor $paybyte1
$rgbValues[($counter*$channelNum+1)] = ($rgbValues[($counter*$channelNum+1)] -band 0xf0) -bor $paybyte2
$rgbValues[($counter*$channelNum+2)] = ($rgbValues[($counter*$channelNum+2)] -band 0xf0) -bor $paybyte3
}

# Copy the array of RGB values back to the bitmap
Expand Down