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Update rom_ctrl scrambling logic #90

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Update rom_ctrl scrambling logic #90

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09b1071
[ot] hw/opentitan: ot_rom_ctrl: Increase PRINCE rounds
AlexJones0 Dec 17, 2024
851b941
[ot] hw/opentitan: ot_rom_ctrl: Remove S&P from data scrambling
AlexJones0 Dec 17, 2024
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33 changes: 2 additions & 31 deletions hw/opentitan/ot_rom_ctrl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,7 @@ static const char *REG_NAMES[REGS_COUNT] = {

#define OT_ROM_CTRL_NUM_ADDR_SUBST_PERM_ROUNDS 2u
#define OT_ROM_CTRL_NUM_DATA_SUBST_PERM_ROUNDS 2u
#define OT_ROM_CTRL_NUM_PRINCE_HALF_ROUNDS 2u
#define OT_ROM_CTRL_NUM_PRINCE_HALF_ROUNDS 3u

#define OT_ROM_CTRL_DATA_BITS (sizeof(uint32_t) * 8u)
#define OT_ROM_CTRL_ECC_BITS 7u
Expand All @@ -121,10 +121,6 @@ static const char *REG_NAMES[REGS_COUNT] = {
static const uint8_t SBOX4[16u] = {
12u, 5u, 6u, 11u, 9u, 0u, 10u, 13u, 3u, 14u, 15u, 8u, 4u, 7u, 1u, 2u
};

static const uint8_t SBOX4_INV[16u] = {
5u, 14u, 15u, 8u, 12u, 1u, 2u, 13u, 11u, 4u, 6u, 3u, 0u, 7u, 9u, 10u
};
/* clang-format on */

static const OtKMACAppCfg KMAC_APP_CFG =
Expand Down Expand Up @@ -281,36 +277,12 @@ static uint64_t ot_rom_ctrl_subst_perm_enc(uint64_t in, uint64_t key,
return state;
}

static uint64_t ot_rom_ctrl_subst_perm_dec(uint64_t in, uint64_t key,
unsigned width, unsigned num_rounds)
{
uint64_t state = in;

for (unsigned ix = 0; ix < num_rounds; ix++) {
state ^= key;
state = ot_rom_ctrl_perm(state, width, true);
state = ot_rom_ctrl_flip(state, width);
state = ot_rom_ctrl_sbox(state, width, SBOX4_INV);
}

state ^= key;

return state;
}

static unsigned ot_rom_ctrl_addr_sp_enc(const OtRomCtrlState *s, unsigned addr)
{
return ot_rom_ctrl_subst_perm_enc(addr, s->addr_nonce, s->addr_width,
OT_ROM_CTRL_NUM_ADDR_SUBST_PERM_ROUNDS);
}

static uint64_t ot_rom_ctrl_data_sp_dec(const OtRomCtrlState *s, uint64_t in)
{
(void)s;
return ot_rom_ctrl_subst_perm_dec(in, 0, OT_ROM_CTRL_WORD_BITS,
OT_ROM_CTRL_NUM_DATA_SUBST_PERM_ROUNDS);
}

static uint64_t
ot_rom_ctrl_get_keystream(const OtRomCtrlState *s, unsigned addr)
{
Expand Down Expand Up @@ -438,8 +410,7 @@ static uint64_t
ot_rom_ctrl_unscramble_word(const OtRomCtrlState *s, unsigned addr, uint64_t in)
{
uint64_t keystream = ot_rom_ctrl_get_keystream(s, addr);
uint64_t sp = ot_rom_ctrl_data_sp_dec(s, in);
return keystream ^ sp;
return keystream ^ in;
}

static uint32_t ot_rom_ctrl_verify_ecc_39_32_u32(
Expand Down
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