SdlsAuthMask.hpp

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// ======================================================================
// \title  SdlsAuthMask.hpp
// \brief  SDLS additional authenticated data (AAD) construction
// ======================================================================

#ifndef Svc_Ccsds_Utils_SdlsAuthMask_HPP
#define Svc_Ccsds_Utils_SdlsAuthMask_HPP

#include <cstring>
#include "Fw/FPrimeBasicTypes.hpp"

namespace Svc {
namespace Ccsds {
namespace Utils {

// AES-GCM authenticates, but does not encrypt, a block of frame fields supplied as AAD. SDLS
// uses this to bind a frame to its virtual channel and security association. The block is a
// masked copy of the frame header: fields that differ between the two ends are zeroed.

struct SdlsTcAuthMask final {
    static constexpr FwSizeType TC_PRIMARY_HEADER_SIZE = 5;
    static constexpr FwSizeType SPI_SIZE = 2;
    static constexpr FwSizeType IV_SIZE = 12;
    static constexpr FwSizeType SIZE = TC_PRIMARY_HEADER_SIZE + SPI_SIZE + IV_SIZE;

    static constexpr U8 VCID_MASK = 0xFC;
    static constexpr FwSizeType VCID_BYTE_INDEX = 2;
    static constexpr U8 VCID_SHIFT = 2;

    U8 bytes[SIZE];

    SdlsTcAuthMask(U8 vcId, U16 securityAssociationIndex) {
        (void)::memset(this->bytes, 0, SIZE);
        this->bytes[VCID_BYTE_INDEX] = static_cast<U8>((vcId << VCID_SHIFT) & VCID_MASK);
        this->bytes[TC_PRIMARY_HEADER_SIZE] = static_cast<U8>(securityAssociationIndex >> 8);
        this->bytes[TC_PRIMARY_HEADER_SIZE + 1] = static_cast<U8>(securityAssociationIndex & 0xFF);
    }
};

struct SdlsTmAuthMask final {
    static constexpr FwSizeType TM_PRIMARY_HEADER_SIZE = 6;
    static constexpr FwSizeType SPI_SIZE = 2;
    static constexpr FwSizeType IV_SIZE = 12;
    static constexpr FwSizeType SIZE = TM_PRIMARY_HEADER_SIZE + SPI_SIZE + IV_SIZE;

    static constexpr U8 VCID_MASK = 0x0E;
    static constexpr FwSizeType VCID_BYTE_INDEX = 1;
    static constexpr U8 VCID_SHIFT = 1;

    U8 bytes[SIZE];

    SdlsTmAuthMask(U8 vcId, U16 securityAssociationIndex) {
        (void)::memset(this->bytes, 0, SIZE);
        this->bytes[VCID_BYTE_INDEX] = static_cast<U8>((vcId << VCID_SHIFT) & VCID_MASK);
        this->bytes[TM_PRIMARY_HEADER_SIZE] = static_cast<U8>(securityAssociationIndex >> 8);
        this->bytes[TM_PRIMARY_HEADER_SIZE + 1] = static_cast<U8>(securityAssociationIndex & 0xFF);
    }
};

}  // namespace Utils
}  // namespace Ccsds
}  // namespace Svc

#endif