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[Decrypters] Introduction of protection_scheme to Widevine PSSH #1652

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Aug 23, 2024
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[Decrypters] Introduction of protection_scheme to Widevine PSSH #1652

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22 changes: 18 additions & 4 deletions src/decrypters/Helpers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,16 @@ namespace
constexpr uint8_t PSSHBOX_HEADER_PSSH[4] = {0x70, 0x73, 0x73, 0x68};
constexpr uint8_t PSSHBOX_HEADER_VER0[4] = {0x00, 0x00, 0x00, 0x00};

// Protection scheme identifying the encryption algorithm. The protection
// scheme is represented as a uint32 value. The uint32 contains 4 bytes each
// representing a single ascii character in one of the 4CC protection scheme values.
enum class WIDEVINE_PROT_SCHEME {
CENC = 0x63656E63,
CBC1 = 0x63626331,
CENS = 0x63656E73,
CBCS = 0x63626373
};

/*!
* \brief Make a protobuf tag.
* \param fieldNumber The field number
Expand All @@ -38,8 +48,8 @@ int MakeProtobufTag(int fieldNumber, int wireType)
return (fieldNumber << 3) | wireType;
}

// \brief Write the size value to the data as varint format
void WriteProtobufVarintSize(std::vector<uint8_t>& data, int size)
// \brief Write a protobuf varint value to the data
void WriteProtobufVarint(std::vector<uint8_t>& data, int size)
{
do
{
Expand Down Expand Up @@ -220,7 +230,7 @@ bool DRM::MakeWidevinePsshData(const std::vector<uint8_t>& kid,

// Create "key_id" field, id: 2 (can be repeated if multiples)
wvPsshData.push_back(MakeProtobufTag(2, 2));
WriteProtobufVarintSize(wvPsshData, static_cast<int>(kid.size()));
WriteProtobufVarint(wvPsshData, static_cast<int>(kid.size())); // Write data size
wvPsshData.insert(wvPsshData.end(), kid.begin(), kid.end());

// Prepare "content_id" data
Expand All @@ -241,9 +251,13 @@ bool DRM::MakeWidevinePsshData(const std::vector<uint8_t>& kid,

// Create "content_id" field, id: 4
wvPsshData.push_back(MakeProtobufTag(4, 2));
WriteProtobufVarintSize(wvPsshData, static_cast<int>(contentIdData.size()));
WriteProtobufVarint(wvPsshData, static_cast<int>(contentIdData.size())); // Write data size
wvPsshData.insert(wvPsshData.end(), contentIdData.begin(), contentIdData.end());

// Create "protection_scheme" field, id: 9
// wvPsshData.push_back(MakeProtobufTag(9, 0));
// WriteProtobufVarint(wvPsshData, static_cast<int>(WIDEVINE_PROT_SCHEME::CENC));

return true;
}

Expand Down