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diff --git a/src/common/Makefile.am b/src/common/Makefile.am
index 5153428dc..9ecbffe8f 100644
--- a/src/common/Makefile.am
+++ b/src/common/Makefile.am
@@ -8,7 +8,8 @@ dist_noinst_DATA = \
LICENSE.compat_getopt compat_getopt.txt \
compat_getopt_main.c \
README.compat_strlcpy compat_strlcpy.3
-noinst_HEADERS = compat_strlcat.h compat_strlcpy.h compat_strnlen.h compat_getpass.h compat_getopt.h simclist.h libpkcs11.h libscdl.h
+noinst_HEADERS = compat_strlcat.h compat_strlcpy.h compat_strnlen.h compat_getpass.h \
+ compat_getopt.h simclist.h libpkcs11.h libscdl.h constant-time.h
AM_CPPFLAGS = -I$(top_srcdir)/src
@@ -43,7 +44,8 @@ TIDY_FILES = \
compat_report_rangecheckfailure.c \
compat___iob_func.c \
simclist.c simclist.h \
- libpkcs11.c libscdl.c
+ libpkcs11.c libscdl.c \
+ constant-time.h
check-local:
if [ -x "$(CLANGTIDY)" ]; then clang-tidy -config='' -header-filter=.* $(TIDY_FILES) -- $(TIDY_FLAGS); fi
diff --git a/src/common/constant-time.h b/src/common/constant-time.h
new file mode 100644
index 0000000000..40c3e500c2
--- /dev/null
+++ b/src/common/constant-time.h
@@ -0,0 +1,134 @@
+/* Original source: https://github.com/openssl/openssl/blob/9890cc42daff5e2d0cad01ac4bf78c391f599a6e/include/internal/constant_time.h */
+
+#ifndef CONSTANT_TIME_H
+#define CONSTANT_TIME_H
+
+#include <stdlib.h>
+#include <string.h>
+
+#if !defined(inline)
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
+#define constant_inline inline
+#elif defined(__GNUC__) && __GNUC__ >= 2
+#elif defined(__GNUC__) && __GNUC__ >= 2
+#elif defined(_MSC_VER)
+#define constant_inline __inline
+#else
+#define constant_inline
+#endif
+#else /* use what caller wants as inline may be from config.h */
+#define constant_inline inline /* inline */
+#endif
+
+/*-
+ * The boolean methods return a bitmask of all ones (0xff...f) for true
+ * and 0 for false. For example,
+ * if (a < b) {
+ * c = a;
+ * } else {
+ * c = b;
+ * }
+ * can be written as
+ * unsigned int lt = constant_time_lt(a, b);
+ * c = constant_time_select(lt, a, b);
+ */
+
+static constant_inline unsigned int
+value_barrier(unsigned int a)
+{
+ volatile unsigned int r = a;
+ return r;
+}
+
+static constant_inline size_t
+value_barrier_s(size_t a)
+{
+ volatile size_t r = a;
+ return r;
+}
+
+/* MSB */
+static constant_inline size_t
+constant_time_msb_s(size_t a)
+{
+ return 0 - (a >> (sizeof(a) * 8 - 1));
+}
+
+static constant_inline unsigned int
+constant_time_msb(unsigned int a)
+{
+ return 0 - (a >> (sizeof(a) * 8 - 1));
+}
+
+/* Select */
+static constant_inline unsigned int
+constant_time_select(unsigned int mask, unsigned int a, unsigned int b)
+{
+ return (value_barrier(mask) & a) | (value_barrier(~mask) & b);
+}
+
+static constant_inline unsigned char
+constant_time_select_8(unsigned char mask, unsigned char a, unsigned char b)
+{
+ return (unsigned char)constant_time_select(mask, a, b);
+}
+
+static constant_inline size_t
+constant_time_select_s(size_t mask, size_t a, size_t b)
+{
+ return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b);
+}
+
+/* Zero */
+static constant_inline unsigned int
+constant_time_is_zero(unsigned int a)
+{
+ return constant_time_msb(~a & (a - 1));
+}
+
+static constant_inline size_t
+constant_time_is_zero_s(size_t a)
+{
+ return constant_time_msb_s(~a & (a - 1));
+}
+
+/* Comparison*/
+static constant_inline size_t
+constant_time_lt_s(size_t a, size_t b)
+{
+ return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b)));
+}
+
+static constant_inline unsigned int
+constant_time_lt(unsigned int a, unsigned int b)
+{
+ return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
+}
+
+static constant_inline unsigned int
+constant_time_ge(unsigned int a, unsigned int b)
+{
+ return ~constant_time_lt(a, b);
+}
+
+/* Equality*/
+
+static constant_inline unsigned int
+constant_time_eq(unsigned int a, unsigned int b)
+{
+ return constant_time_is_zero(a ^ b);
+}
+
+static constant_inline size_t
+constant_time_eq_s(size_t a, size_t b)
+{
+ return constant_time_is_zero_s(a ^ b);
+}
+
+static constant_inline unsigned int
+constant_time_eq_i(int a, int b)
+{
+ return constant_time_eq((unsigned int)a, (unsigned int)b);
+}
+
+#endif /* CONSTANT_TIME_H */
diff --git a/src/libopensc/internal.h b/src/libopensc/internal.h
index 74014235a..13eccfa1a 100644
--- a/src/libopensc/internal.h
+++ b/src/libopensc/internal.h
@@ -168,6 +168,8 @@ int sc_pkcs1_strip_01_padding(struct sc_context *ctx, const u8 *in_dat, size_t i
u8 *out_dat, size_t *out_len);
int sc_pkcs1_strip_02_padding(struct sc_context *ctx, const u8 *data, size_t len,
u8 *out_dat, size_t *out_len);
+int sc_pkcs1_strip_02_padding_constant_time(sc_context_t *ctx, unsigned int n, const u8 *data,
+ unsigned int data_len, u8 *out, unsigned int *out_len);
int sc_pkcs1_strip_digest_info_prefix(unsigned int *algorithm,
const u8 *in_dat, size_t in_len, u8 *out_dat, size_t *out_len);
diff --git a/src/libopensc/padding.c b/src/libopensc/padding.c
index ca47733a4e..ddb3061134 100644
--- a/src/libopensc/padding.c
+++ b/src/libopensc/padding.c
@@ -32,10 +32,13 @@
#include <string.h>
#include <stdlib.h>
+#include "common/constant-time.h"
#include "internal.h"
/* TODO doxygen comments */
+#define SC_PKCS1_PADDING_MIN_SIZE 11
+
/*
* Prefixes for pkcs-v1 signatures
*/
@@ -144,44 +147,82 @@ sc_pkcs1_strip_01_padding(struct sc_cont
}
-/* remove pkcs1 BT02 padding (adding BT02 padding is currently not
- * needed/implemented) */
+/* Remove pkcs1 BT02 padding (adding BT02 padding is currently not
+ * needed/implemented) in constant-time.
+ * Original source: https://github.com/openssl/openssl/blob/9890cc42daff5e2d0cad01ac4bf78c391f599a6e/crypto/rsa/rsa_pk1.c#L171 */
int
-sc_pkcs1_strip_02_padding(sc_context_t *ctx, const u8 *data, size_t len, u8 *out, size_t *out_len)
+sc_pkcs1_strip_02_padding_constant_time(sc_context_t *ctx, unsigned int n, const u8 *data, unsigned int data_len, u8 *out, unsigned int *out_len)
{
- unsigned int n = 0;
-
+ unsigned int i = 0;
+ u8 *msg, *msg_orig = NULL;
+ unsigned int good, found_zero_byte, mask;
+ unsigned int zero_index = 0, msg_index, mlen = -1, len = 0;
LOG_FUNC_CALLED(ctx);
- if (data == NULL || len < 3)
+
+ if (data == NULL || data_len <= 0 || data_len > n || n < SC_PKCS1_PADDING_MIN_SIZE)
LOG_FUNC_RETURN(ctx, SC_ERROR_INTERNAL);
- /* skip leading zero byte */
- if (*data == 0) {
- data++;
- len--;
+ msg = msg_orig = calloc(n, sizeof(u8));
+ if (msg == NULL)
+ LOG_FUNC_RETURN(ctx, SC_ERROR_INTERNAL);
+
+ /*
+ * We can not check length of input data straight away and still we need to read
+ * from input even when the input is not as long as needed to keep the time constant.
+ * If data has wrong size, it is padded by zeroes from left and the following checks
+ * do not pass.
+ */
+ len = data_len;
+ for (data += len, msg += n, i = 0; i < n; i++) {
+ mask = ~constant_time_is_zero(len);
+ len -= 1 & mask;
+ data -= 1 & mask;
+ *--msg = *data & mask;
+ }
+ // check first byte to be 0x00
+ good = constant_time_is_zero(msg[0]);
+ // check second byte to be 0x02
+ good &= constant_time_eq(msg[1], 2);
+
+ // find zero byte after random data in padding
+ found_zero_byte = 0;
+ for (i = 2; i < n; i++) {
+ unsigned int equals0 = constant_time_is_zero(msg[i]);
+ zero_index = constant_time_select(~found_zero_byte & equals0, i, zero_index);
+ found_zero_byte |= equals0;
}
- if (data[0] != 0x02)
- LOG_FUNC_RETURN(ctx, SC_ERROR_WRONG_PADDING);
- /* skip over padding bytes */
- for (n = 1; n < len && data[n]; n++)
- ;
- /* Must be at least 8 pad bytes */
- if (n >= len || n < 9)
- LOG_FUNC_RETURN(ctx, SC_ERROR_WRONG_PADDING);
- n++;
- if (out == NULL)
- /* just check the padding */
- LOG_FUNC_RETURN(ctx, SC_SUCCESS);
- /* Now move decrypted contents to head of buffer */
- if (*out_len < len - n)
- LOG_FUNC_RETURN(ctx, SC_ERROR_INTERNAL);
- *out_len = len - n;
- memmove(out, data + n, *out_len);
+ // zero_index stands for index of last found zero
+ good &= constant_time_ge(zero_index, 2 + 8);
+
+ // start of the actual message in data
+ msg_index = zero_index + 1;
+
+ // length of message
+ mlen = data_len - msg_index;
+
+ // check that message fits into out buffer
+ good &= constant_time_ge(*out_len, 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);
+ 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++) {
+ 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]);
+ }
- sc_log(ctx, "stripped output(%"SC_FORMAT_LEN_SIZE_T"u): %s", len - n,
- sc_dump_hex(out, len - n));
- LOG_FUNC_RETURN(ctx, len - n);
+ free(msg_orig);
+ return constant_time_select(good, mlen, SC_ERROR_WRONG_PADDING);
}
/* add/remove DigestInfo prefix */
diff --git a/src/libopensc/pkcs15-sec.c b/src/libopensc/pkcs15-sec.c
index a019af460f..f7ee819d65 100644
--- a/src/libopensc/pkcs15-sec.c
+++ b/src/libopensc/pkcs15-sec.c
@@ -286,12 +286,14 @@ int sc_pkcs15_decipher(struct sc_pkcs15_
/* Strip any padding */
if (pad_flags & SC_ALGORITHM_RSA_PAD_PKCS1) {
- size_t s = r;
- r = sc_pkcs1_strip_02_padding(ctx, out, s, out, &s);
- LOG_TEST_RET(ctx, r, "Invalid PKCS#1 padding");
+ unsigned int s = r;
+ unsigned int key_size = (unsigned int)alg_info->key_length;
+ r = sc_pkcs1_strip_02_padding_constant_time(ctx, key_size / 8, out, s, out, &s);
+ /* for keeping PKCS#1 v1.5 depadding constant-time, do not log error here */
}
- LOG_FUNC_RETURN(ctx, r);
+ /* do not log error code to prevent side channel attack */
+ return r;
}
/* derive one key from another. RSA can use decipher, so this is for only ECDH
diff --git a/src/pkcs11/framework-pkcs15.c b/src/pkcs11/framework-pkcs15.c
index f75a3dbaec..632681df63 100644
--- a/src/pkcs11/framework-pkcs15.c
+++ b/src/pkcs11/framework-pkcs15.c
@@ -18,6 +18,7 @@
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
+#include "common/constant-time.h"
#include "config.h"
#include <stdlib.h>
#include <string.h>
@@ -4174,7 +4175,8 @@ pkcs15_prkey_decrypt(struct sc_pkcs11_se
struct pkcs15_fw_data *fw_data = NULL;
struct pkcs15_prkey_object *prkey;
unsigned char decrypted[512]; /* FIXME: Will not work for keys above 4096 bits */
- int buff_too_small, rv, flags = 0, prkey_has_path = 0;
+ int rv, flags = 0, prkey_has_path = 0;
+ CK_ULONG mask, good, rv_pkcs11;
sc_log(context, "Initiating decryption.");
@@ -4246,27 +4248,54 @@ pkcs15_prkey_decrypt(struct sc_pkcs11_se
rv = sc_pkcs15_decipher(fw_data->p15_card, prkey->prv_p15obj, flags,
pEncryptedData, ulEncryptedDataLen, decrypted, sizeof(decrypted));
- if (rv < 0 && !sc_pkcs11_conf.lock_login && !prkey_has_path)
+ /* skip for PKCS#1 v1.5 padding prevent side channel attack */
+ if (!(flags & SC_ALGORITHM_RSA_PAD_PKCS1) &&
+ rv < 0 && !sc_pkcs11_conf.lock_login && !prkey_has_path)
if (reselect_app_df(fw_data->p15_card) == SC_SUCCESS)
rv = sc_pkcs15_decipher(fw_data->p15_card, prkey->prv_p15obj, flags,
pEncryptedData, ulEncryptedDataLen, decrypted, sizeof(decrypted));
sc_unlock(p11card->card);
- sc_log(context, "Decryption complete. Result %d.", rv);
+ sc_log(context, "Decryption complete.");
- if (rv < 0)
+ /* Handle following code in constant-time
return sc_to_cryptoki_error(rv, "C_Decrypt");
+ * to prevent Marvin attack for PKCS#1 v1.5 padding. */
- buff_too_small = (*pulDataLen < (CK_ULONG)rv);
- *pulDataLen = rv;
- if (pData == NULL_PTR)
- return CKR_OK;
- if (buff_too_small)
- return CKR_BUFFER_TOO_SMALL;
- memcpy(pData, decrypted, *pulDataLen);
-
- return CKR_OK;
+ /* only padding error must be handled in constant-time way,
+ * other error can be returned straight away */
+ if ((~constant_time_eq_i(rv, SC_ERROR_WRONG_PADDING) & constant_time_lt_s(sizeof(decrypted), (size_t)rv)))
+ return sc_to_cryptoki_error(rv, "C_Decrypt");
+
+ /* check rv for padding error */
+ good = ~constant_time_eq_i(rv, SC_ERROR_WRONG_PADDING);
+ rv_pkcs11 = sc_to_cryptoki_error(SC_ERROR_WRONG_PADDING, "C_Decrypt");
+ rv_pkcs11 = constant_time_select_s(good, CKR_OK, rv_pkcs11);
+
+ if (pData == NULL_PTR) {
+ /* set length only if no error */
+ *pulDataLen = constant_time_select_s(good, rv, *pulDataLen);
+ /* return error only if original rv < 0 */
+ return rv_pkcs11;
+ }
+
+ /* check whether *pulDataLen < rv and set return value for small output buffer */
+ mask = good & constant_time_lt_s(*pulDataLen, rv);
+ rv_pkcs11 = constant_time_select_s(mask, CKR_BUFFER_TOO_SMALL, rv_pkcs11);
+ good &= ~mask;
+
+ /* move everything from decrypted into out buffer constant-time, if rv is ok */
+ for (CK_ULONG i = 0; i < *pulDataLen; i++) { /* iterate over whole pData to not disclose real depadded length */
+ CK_ULONG msg_index;
+ mask = good & constant_time_lt_s(i, sizeof(decrypted)); /* i should be in the bounds of decrypted */
+ mask &= constant_time_lt_s(i, constant_time_select_s(good, rv, 0)); /* check that is in bounds of depadded message */
+ msg_index = constant_time_select_s(mask, i, 0);
+ pData[i] = constant_time_select_8(mask, decrypted[msg_index], pData[i]);
+ }
+ *pulDataLen = constant_time_select_s(good, rv, *pulDataLen);
+ /* do not log error code to prevent side channel attack */
+ return rv_pkcs11;
}
diff --git a/src/pkcs11/mechanism.c b/src/pkcs11/mechanism.c
index 03495265a4..d3f0434231 100644
--- a/src/pkcs11/mechanism.c
+++ b/src/pkcs11/mechanism.c
@@ -23,6 +23,7 @@
#include <stdlib.h>
#include <string.h>
+#include "common/constant-time.h"
#include "sc-pkcs11.h"
/* Also used for verification data */
@@ -1089,7 +1090,9 @@ sc_pkcs11_decr(struct sc_pkcs11_session
rv = op->type->decrypt(op, pEncryptedData, ulEncryptedDataLen,
pData, pulDataLen);
- if (rv != CKR_BUFFER_TOO_SMALL && pData != NULL)
+ /* terminate session for any return value except CKR_BUFFER_TOO_SMALL,
+ * perform check in time side-channel free way to prevent Marvin attack */
+ if (!constant_time_eq_s(rv, CKR_BUFFER_TOO_SMALL) && pData != NULL)
session_stop_operation(session, SC_PKCS11_OPERATION_DECRYPT);
return rv;
diff --git a/src/pkcs11/pkcs11-object.c b/src/pkcs11/pkcs11-object.c
index f04c0b4c56..b023911213 100644
--- a/src/pkcs11/pkcs11-object.c
+++ b/src/pkcs11/pkcs11-object.c
@@ -926,7 +926,8 @@ CK_RV C_Decrypt(CK_SESSION_HANDLE hSessi
rv = reset_login_state(session->slot, rv);
}
- sc_log(context, "C_Decrypt() = %s", lookup_enum ( RV_T, rv ));
+ /* do not log error code to prevent side channel attack */
+ sc_log(context, "C_Decrypt() finished");
sc_pkcs11_unlock();
return rv;
}
diff --git a/src/pkcs11/misc.c b/src/pkcs11/misc.c
index 5ca1176b1d..1d893d6181 100644
--- a/src/pkcs11/misc.c
+++ b/src/pkcs11/misc.c
@@ -23,6 +23,7 @@
#include <stdlib.h>
#include <string.h>
+#include "common/constant-time.h"
#include "sc-pkcs11.h"
#define DUMP_TEMPLATE_MAX 32
@@ -174,7 +175,7 @@ CK_RV reset_login_state(struct sc_pkcs11_slot *slot, CK_RV rv)
slot->p11card->framework->logout(slot);
}
- if (rv == CKR_USER_NOT_LOGGED_IN) {
+ if (constant_time_eq_s(rv, CKR_USER_NOT_LOGGED_IN)) {
slot->login_user = -1;
pop_all_login_states(slot);
}
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