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Set correct output length in PKCS#1 v1.5 depadding #3077

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merged 4 commits into from
Apr 4, 2024
Merged

Set correct output length in PKCS#1 v1.5 depadding #3077

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26bea00
padding: Set correct output length in PKCS#1 v1.5 depadding
xhanulik Mar 19, 2024
cc9e84d
minidriver: Remove logging to prevent Marvin attack
xhanulik Mar 20, 2024
5a7bffc
unittests: Test correct output length for PKCS#1 v1.5 depadding
xhanulik Mar 20, 2024
780e08b
minidriver: Refactor inversion of decrypted buffer
xhanulik Mar 21, 2024
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15 changes: 9 additions & 6 deletions src/libopensc/padding.c
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Original file line number Diff line number Diff line change
Expand Up @@ -154,13 +154,15 @@ sc_pkcs1_strip_02_padding_constant_time(sc_context_t *ctx, unsigned int n, const
{
unsigned int i = 0;
u8 *msg, *msg_orig = NULL;
unsigned int good, found_zero_byte, mask;
unsigned int good, found_zero_byte, mask, tmp_outlen;
unsigned int zero_index = 0, msg_index, mlen = -1, len = 0;
LOG_FUNC_CALLED(ctx);

if (data == NULL || data_len <= 0 || data_len > n || n < SC_PKCS1_PADDING_MIN_SIZE)
if (data == NULL || data_len <= 0 || data_len > n ||
n < SC_PKCS1_PADDING_MIN_SIZE || out_len == NULL)
LOG_FUNC_RETURN(ctx, SC_ERROR_INTERNAL);

tmp_outlen = *out_len;
msg = msg_orig = calloc(n, sizeof(u8));
if (msg == NULL)
LOG_FUNC_RETURN(ctx, SC_ERROR_INTERNAL);
Expand Down Expand Up @@ -201,25 +203,26 @@ sc_pkcs1_strip_02_padding_constant_time(sc_context_t *ctx, unsigned int n, const
mlen = data_len - msg_index;

// check that message fits into out buffer
good &= constant_time_ge(*out_len, mlen);
good &= constant_time_ge(tmp_outlen, mlen);

// move the result in-place by |num|-SC_PKCS1_PADDING_MIN_SIZE-|mlen| bytes to the left.
*out_len = constant_time_select(constant_time_lt(n - SC_PKCS1_PADDING_MIN_SIZE, *out_len),
n - SC_PKCS1_PADDING_MIN_SIZE, *out_len);
tmp_outlen = constant_time_select(constant_time_lt(n - SC_PKCS1_PADDING_MIN_SIZE, tmp_outlen),
n - SC_PKCS1_PADDING_MIN_SIZE, tmp_outlen);
for (msg_index = 1; msg_index < n - SC_PKCS1_PADDING_MIN_SIZE; msg_index <<= 1) {
mask = ~constant_time_eq(msg_index & (n - SC_PKCS1_PADDING_MIN_SIZE - mlen), 0);
for (i = SC_PKCS1_PADDING_MIN_SIZE; i < n - msg_index; i++)
msg[i] = constant_time_select_8(mask, msg[i + msg_index], msg[i]);
}
// move message into out buffer, if good
for (i = 0; i < *out_len; i++) {
for (i = 0; i < tmp_outlen; i++) {
unsigned int msg_index;
// when out is longer than message in data, use some bogus index in msg
mask = good & constant_time_lt(i, mlen);
msg_index = constant_time_select(mask, i + SC_PKCS1_PADDING_MIN_SIZE, 0); // to now overflow msg buffer
out[i] = constant_time_select_8(mask, msg[msg_index], out[i]);
}

*out_len = constant_time_select(good, mlen, *out_len);
free(msg_orig);
return constant_time_select(good, mlen, SC_ERROR_WRONG_PADDING);
}
Expand Down
18 changes: 8 additions & 10 deletions src/minidriver/minidriver.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4710,7 +4710,7 @@ DWORD WINAPI CardRSADecrypt(__in PCARD_DATA pCardData,
goto err;
}

good = constant_time_eq_i(r, 0);
good = constant_time_ge(r, 1);
/* if no error or padding error, do not return here to prevent Marvin attack */
if (!(good | wrong_padding) && r < 0) {
logprintf(pCardData, 2, "sc_pkcs15_decipher error(%i): %s\n", r, sc_strerror(r));
Expand All @@ -4721,18 +4721,16 @@ DWORD WINAPI CardRSADecrypt(__in PCARD_DATA pCardData,
}
dwret = constant_time_select_s(good, SCARD_S_SUCCESS, SCARD_F_INTERNAL_ERROR);

logprintf(pCardData, 2, "decrypted data(%lu):\n",
(unsigned long)pInfo->cbData);
loghex(pCardData, 7, pbuf2, pInfo->cbData);

/*inversion donnees */
/* copy data in constant-time way to prevent leak */
for (ui = 0; ui < pbufLen; ui++) {
unsigned int mask, msg_index, inv_ui;
mask = good & constant_time_lt_s(ui, pInfo->cbData); /* ui should be in the bounds of pbuf2 */
inv_ui = pInfo->cbData - ui - 1;
msg_index = constant_time_select_s(mask, inv_ui, 0);
pInfo->pbData[ui] = constant_time_select_8(mask, pbuf2[msg_index], pInfo->pbData[ui]);
unsigned int mask, inv_ui;
unsigned char msg_byte, orig_byte;
mask = good & constant_time_lt_s(ui, pInfo->cbData); /* ui should be in bounds of decrypted message */
inv_ui = pInfo->cbData - ui - 1; /* compute inversed ui index */
msg_byte = pbuf2[constant_time_select(mask, inv_ui, 0)]; /* if in range of decrypted message, read on inversed index otherwise read some bogus value */
orig_byte = pInfo->pbData[ui];
pInfo->pbData[ui] = constant_time_select_s(mask, msg_byte, orig_byte); /* store message byte only if in correct range */
}

pCardData->pfnCspFree(pbuf);
Expand Down
11 changes: 11 additions & 0 deletions src/tests/unittests/strip_pkcs1_2_padding.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ torture_long_output_buffer(void **state)
unsigned char result_msg[] = {'m', 's', 'g'};
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal(r, 3);
assert_int_equal(r, (int)out_len);
assert_memory_equal(out, result_msg, r);
free(out);
}
Expand All @@ -34,6 +35,7 @@ torture_short_output_buffer(void **state)
unsigned int out_len = 1;
unsigned char *out = calloc(out_len, sizeof(unsigned char));
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal((int)out_len, 1);
assert_int_equal(r, SC_ERROR_WRONG_PADDING);
free(out);
}
Expand All @@ -52,6 +54,7 @@ torture_short_message_correct_padding(void **state)
unsigned char result_msg[] = {'m', 's', 'g'};
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal(r, 3);
assert_int_equal(r, (int)out_len);
assert_memory_equal(out, result_msg, r);
free(out);
}
Expand All @@ -68,6 +71,7 @@ torture_missing_first_zero(void **state)
unsigned int out_len = 10;
unsigned char *out = calloc(out_len, sizeof(unsigned char));
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal((int)out_len, 10);
assert_int_equal(r, SC_ERROR_WRONG_PADDING);
free(out);
}
Expand All @@ -84,6 +88,7 @@ torture_missing_two(void **state)
unsigned int out_len = 10;
unsigned char *out = calloc(out_len, sizeof(unsigned char));
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal((int)out_len, 10);
assert_int_equal(r, SC_ERROR_WRONG_PADDING);
free(out);
}
Expand All @@ -100,6 +105,7 @@ torture_short_padding(void **state)
unsigned int out_len = 10;
unsigned char *out = calloc(out_len, sizeof(unsigned char));
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal((int)out_len, 10);
assert_int_equal(r, SC_ERROR_WRONG_PADDING);
free(out);
}
Expand All @@ -115,6 +121,7 @@ torture_missing_second_zero(void **state)
unsigned int out_len = 10;
unsigned char *out = calloc(out_len, sizeof(unsigned char));
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal((int)out_len, 10);
assert_int_equal(r, SC_ERROR_WRONG_PADDING);
free(out);
}
Expand All @@ -130,6 +137,7 @@ torture_missing_message(void **state)
unsigned int out_len = 11;
unsigned char *out = calloc(out_len, sizeof(unsigned char));
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal((int)out_len, 11);
assert_int_equal(r, SC_ERROR_WRONG_PADDING);
free(out);
}
Expand All @@ -148,6 +156,7 @@ torture_one_byte_message(void **state)
unsigned char result_msg[] = {'m'};
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal(r, 1);
assert_int_equal(r, (int)out_len);
assert_memory_equal(out, result_msg, r);
free(out);
}
Expand All @@ -166,6 +175,7 @@ torture_longer_padding(void **state)
unsigned char result_msg[] = {0x9d, 0x98, 0x3d, 0xca, 0xa9, 0xa7, 0x11, 0x0a};
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal(r, 8);
assert_int_equal(r, (int)out_len);
assert_memory_equal(out, result_msg, r);
free(out);
}
Expand All @@ -181,6 +191,7 @@ torture_empty_message(void **state)
unsigned int out_len = 8;
unsigned char *out = calloc(out_len, sizeof(unsigned char));
int r = sc_pkcs1_strip_02_padding_constant_time(NULL, n, in, in_len, out, &out_len);
assert_int_equal((int)out_len, 0);
assert_int_equal(r, 0);
free(out);
}
Expand Down
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