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cxx/random.hh: use uint8_t for random stream enum #1

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cxx/random.hh: use uint8_t for random stream enum #1

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10 changes: 5 additions & 5 deletions cxx/random.hh
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Original file line number Diff line number Diff line change
Expand Up @@ -27,11 +27,11 @@
class Random
{
public:
enum class Stream : uint32_t {
wm_pattern = 0xe58eb537,
wm_mask = 0xfd19fc82,
wm_convcode = 0x7ecf1f7a,
img_comment = 0x7abcde01,
enum class Stream : uint8_t {
wm_pattern = 1,
wm_mask = 2,
wm_convcode = 3,
img_comment = 4,
Comment on lines +31 to +34
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critical

Changing the enum values will alter the generated pseudo-random sequences. This is a critical breaking change that will prevent watermarks created with older versions of this tool from being read correctly.

The Random::seed function was already using only the lower 8 bits of the Stream enum value by casting it to uint8_t.

To maintain backward compatibility, I suggest using the lower 8 bits of the original uint32_t values.

The original values and their lower 8 bits are:

  • wm_pattern: 0xe58eb537 -> 0x37
  • wm_mask: 0xfd19fc82 -> 0x82
  • wm_convcode: 0x7ecf1f7a -> 0x7a
  • img_comment: 0x7abcde01 -> 0x01

These are all unique and would preserve the behavior of the random number generator, making this change non-breaking.

    wm_pattern  = 0x37,
    wm_mask     = 0x82,
    wm_convcode = 0x7a,
    img_comment = 0x01,

};
private:
gcry_cipher_hd_t aes_ctr_cipher = nullptr;
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