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[ot] hw/opentitan: ot_aes: fix IV updates in CFB mode #107

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[ot] hw/opentitan: ot_aes: fix IV updates in CFB mode #107

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18 changes: 14 additions & 4 deletions hw/opentitan/ot_aes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
* QEMU OpenTitan AES device
*
* Copyright (c) 2022-2024 Rivos, Inc.
* Copyright (c) 2025 lowRISC contributors.
*
* Author(s):
* Emmanuel Blot <[email protected]>
Expand Down Expand Up @@ -430,9 +431,11 @@ static void ot_aes_init_keyshare(OtAESState *s, bool randomize)
OtAESRegisters *r = s->regs;
OtAESContext *c = s->ctx;

trace_ot_aes_init("keyshare");
if (randomize) {
trace_ot_aes_init("keyshare init (randomize data)");
ot_aes_randomize(s, r->keyshare, ARRAY_SIZE(r->keyshare));
} else {
trace_ot_aes_init("keyshare init (data preserved)");
}
bitmap_zero(r->keyshare_bm, (int64_t)(PARAM_NUM_REGS_KEY * 2u));
c->key_ready = false;
Expand All @@ -443,9 +446,11 @@ static void ot_aes_init_iv(OtAESState *s, bool randomize)
OtAESRegisters *r = s->regs;
OtAESContext *c = s->ctx;

trace_ot_aes_init("iv");
if (randomize) {
trace_ot_aes_init("iv init (randomize data)");
ot_aes_randomize(s, r->iv, ARRAY_SIZE(r->iv));
} else {
trace_ot_aes_init("iv init (data preserved)");
}
bitmap_zero(r->iv_bm, PARAM_NUM_REGS_IV);
c->iv_ready = false;
Expand Down Expand Up @@ -873,13 +878,18 @@ static void ot_aes_process(OtAESState *s)
c->di_full = false;

if (rc == CRYPT_OK) {
/* IV registers are updated on each round */
/*
* IV registers are updated on each round. For details, see:
* https://opentitan.org/book/hw/ip/aes/doc/theory_of_operation.html
* https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
*/
switch (mode) {
case AES_CBC:
memcpy(c->iv, c->cbc.IV, sizeof(c->iv));
break;
case AES_CFB:
memcpy(c->iv, c->cfb.IV, sizeof(c->iv));
/* In CFB mode the next IV register value is the ciphertext */
memcpy(c->iv, encrypt ? c->dst : c->src, sizeof(c->iv));
break;
case AES_OFB:
memcpy(c->iv, c->ofb.IV, sizeof(c->iv));
Expand Down