Squashed commit upgrading to mbedtls-2.28.1
Squash merging branch import/mbedtls-2.28.1
ebf1f6a58089 ("libmbedtls: compile new files added with 2.28.1")
3ffb51b58a54 ("libmbedtls: add SM2 curve")
c425755720b4 ("libmbedtls: mbedtls_mpi_exp_mod(): optimize mempool usage")
23493c822a82 ("libmbedtls: mbedtls_mpi_exp_mod(): reduce stack usage")
dcdca2348dff ("libmbedtls: mbedtls_mpi_exp_mod() initialize W")
dc2994976958 ("libmbedtls: fix no CRT issue")
c6628873b281 ("libmbedtls: add interfaces in mbedtls for context memory operation")
8acd202d3e55 ("libmedtls: mpi_miller_rabin: increase count limit")
37284e28d5d9 ("libmbedtls: add mbedtls_mpi_init_mempool()")
b499a75f29f3 ("libmbedtls: make mbedtls_mpi_mont*() available")
2080a8c96a5d ("mbedtls: configure mbedtls to reach for config")
e0858334327a ("mbedtls: remove default include/mbedtls/config.h")
dd9688e6b8ce ("Import mbedtls-2.28.1")
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/constant_time.c b/lib/libmbedtls/mbedtls/library/constant_time.c
new file mode 100644
index 0000000..e276d23
--- /dev/null
+++ b/lib/libmbedtls/mbedtls/library/constant_time.c
@@ -0,0 +1,832 @@
+/**
+ * Constant-time functions
+ *
+ * Copyright The Mbed TLS Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+ /*
+ * The following functions are implemented without using comparison operators, as those
+ * might be translated to branches by some compilers on some platforms.
+ */
+
+#include "common.h"
+#include "constant_time_internal.h"
+#include "mbedtls/constant_time.h"
+#include "mbedtls/error.h"
+#include "mbedtls/platform_util.h"
+
+#if defined(MBEDTLS_BIGNUM_C)
+#include "mbedtls/bignum.h"
+#endif
+
+#if defined(MBEDTLS_SSL_TLS_C)
+#include "mbedtls/ssl_internal.h"
+#endif
+
+#if defined(MBEDTLS_RSA_C)
+#include "mbedtls/rsa.h"
+#endif
+
+#if defined(MBEDTLS_BASE64_C)
+#include "constant_time_invasive.h"
+#endif
+
+#include <string.h>
+
+int mbedtls_ct_memcmp( const void *a,
+ const void *b,
+ size_t n )
+{
+ size_t i;
+ volatile const unsigned char *A = (volatile const unsigned char *) a;
+ volatile const unsigned char *B = (volatile const unsigned char *) b;
+ volatile unsigned char diff = 0;
+
+ for( i = 0; i < n; i++ )
+ {
+ /* Read volatile data in order before computing diff.
+ * This avoids IAR compiler warning:
+ * 'the order of volatile accesses is undefined ..' */
+ unsigned char x = A[i], y = B[i];
+ diff |= x ^ y;
+ }
+
+ return( (int)diff );
+}
+
+unsigned mbedtls_ct_uint_mask( unsigned value )
+{
+ /* MSVC has a warning about unary minus on unsigned, but this is
+ * well-defined and precisely what we want to do here */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+ return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+}
+
+#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)
+
+size_t mbedtls_ct_size_mask( size_t value )
+{
+ /* MSVC has a warning about unary minus on unsigned integer types,
+ * but this is well-defined and precisely what we want to do here. */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+ return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+}
+
+#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
+
+#if defined(MBEDTLS_BIGNUM_C)
+
+mbedtls_mpi_uint mbedtls_ct_mpi_uint_mask( mbedtls_mpi_uint value )
+{
+ /* MSVC has a warning about unary minus on unsigned, but this is
+ * well-defined and precisely what we want to do here */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+ return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+}
+
+#endif /* MBEDTLS_BIGNUM_C */
+
+#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)
+
+/** Constant-flow mask generation for "less than" comparison:
+ * - if \p x < \p y, return all-bits 1, that is (size_t) -1
+ * - otherwise, return all bits 0, that is 0
+ *
+ * This function can be used to write constant-time code by replacing branches
+ * with bit operations using masks.
+ *
+ * \param x The first value to analyze.
+ * \param y The second value to analyze.
+ *
+ * \return All-bits-one if \p x is less than \p y, otherwise zero.
+ */
+static size_t mbedtls_ct_size_mask_lt( size_t x,
+ size_t y )
+{
+ /* This has the most significant bit set if and only if x < y */
+ const size_t sub = x - y;
+
+ /* sub1 = (x < y) ? 1 : 0 */
+ const size_t sub1 = sub >> ( sizeof( sub ) * 8 - 1 );
+
+ /* mask = (x < y) ? 0xff... : 0x00... */
+ const size_t mask = mbedtls_ct_size_mask( sub1 );
+
+ return( mask );
+}
+
+size_t mbedtls_ct_size_mask_ge( size_t x,
+ size_t y )
+{
+ return( ~mbedtls_ct_size_mask_lt( x, y ) );
+}
+
+#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
+
+#if defined(MBEDTLS_BASE64_C)
+
+/* Return 0xff if low <= c <= high, 0 otherwise.
+ *
+ * Constant flow with respect to c.
+ */
+MBEDTLS_STATIC_TESTABLE
+unsigned char mbedtls_ct_uchar_mask_of_range( unsigned char low,
+ unsigned char high,
+ unsigned char c )
+{
+ /* low_mask is: 0 if low <= c, 0x...ff if low > c */
+ unsigned low_mask = ( (unsigned) c - low ) >> 8;
+ /* high_mask is: 0 if c <= high, 0x...ff if c > high */
+ unsigned high_mask = ( (unsigned) high - c ) >> 8;
+ return( ~( low_mask | high_mask ) & 0xff );
+}
+
+#endif /* MBEDTLS_BASE64_C */
+
+unsigned mbedtls_ct_size_bool_eq( size_t x,
+ size_t y )
+{
+ /* diff = 0 if x == y, non-zero otherwise */
+ const size_t diff = x ^ y;
+
+ /* MSVC has a warning about unary minus on unsigned integer types,
+ * but this is well-defined and precisely what we want to do here. */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+
+ /* diff_msb's most significant bit is equal to x != y */
+ const size_t diff_msb = ( diff | (size_t) -diff );
+
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+
+ /* diff1 = (x != y) ? 1 : 0 */
+ const unsigned diff1 = diff_msb >> ( sizeof( diff_msb ) * 8 - 1 );
+
+ return( 1 ^ diff1 );
+}
+
+#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
+
+/** Constant-flow "greater than" comparison:
+ * return x > y
+ *
+ * This is equivalent to \p x > \p y, but is likely to be compiled
+ * to code using bitwise operation rather than a branch.
+ *
+ * \param x The first value to analyze.
+ * \param y The second value to analyze.
+ *
+ * \return 1 if \p x greater than \p y, otherwise 0.
+ */
+static unsigned mbedtls_ct_size_gt( size_t x,
+ size_t y )
+{
+ /* Return the sign bit (1 for negative) of (y - x). */
+ return( ( y - x ) >> ( sizeof( size_t ) * 8 - 1 ) );
+}
+
+#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */
+
+#if defined(MBEDTLS_BIGNUM_C)
+
+unsigned mbedtls_ct_mpi_uint_lt( const mbedtls_mpi_uint x,
+ const mbedtls_mpi_uint y )
+{
+ mbedtls_mpi_uint ret;
+ mbedtls_mpi_uint cond;
+
+ /*
+ * Check if the most significant bits (MSB) of the operands are different.
+ */
+ cond = ( x ^ y );
+ /*
+ * If the MSB are the same then the difference x-y will be negative (and
+ * have its MSB set to 1 during conversion to unsigned) if and only if x<y.
+ */
+ ret = ( x - y ) & ~cond;
+ /*
+ * If the MSB are different, then the operand with the MSB of 1 is the
+ * bigger. (That is if y has MSB of 1, then x<y is true and it is false if
+ * the MSB of y is 0.)
+ */
+ ret |= y & cond;
+
+
+ ret = ret >> ( sizeof( mbedtls_mpi_uint ) * 8 - 1 );
+
+ return (unsigned) ret;
+}
+
+#endif /* MBEDTLS_BIGNUM_C */
+
+unsigned mbedtls_ct_uint_if( unsigned condition,
+ unsigned if1,
+ unsigned if0 )
+{
+ unsigned mask = mbedtls_ct_uint_mask( condition );
+ return( ( mask & if1 ) | (~mask & if0 ) );
+}
+
+#if defined(MBEDTLS_BIGNUM_C)
+
+/** Select between two sign values without branches.
+ *
+ * This is functionally equivalent to `condition ? if1 : if0` but uses only bit
+ * operations in order to avoid branches.
+ *
+ * \note if1 and if0 must be either 1 or -1, otherwise the result
+ * is undefined.
+ *
+ * \param condition Condition to test.
+ * \param if1 The first sign; must be either +1 or -1.
+ * \param if0 The second sign; must be either +1 or -1.
+ *
+ * \return \c if1 if \p condition is nonzero, otherwise \c if0.
+ * */
+static int mbedtls_ct_cond_select_sign( unsigned char condition,
+ int if1,
+ int if0 )
+{
+ /* In order to avoid questions about what we can reasonably assume about
+ * the representations of signed integers, move everything to unsigned
+ * by taking advantage of the fact that if1 and if0 are either +1 or -1. */
+ unsigned uif1 = if1 + 1;
+ unsigned uif0 = if0 + 1;
+
+ /* condition was 0 or 1, mask is 0 or 2 as are uif1 and uif0 */
+ const unsigned mask = condition << 1;
+
+ /* select uif1 or uif0 */
+ unsigned ur = ( uif0 & ~mask ) | ( uif1 & mask );
+
+ /* ur is now 0 or 2, convert back to -1 or +1 */
+ return( (int) ur - 1 );
+}
+
+void mbedtls_ct_mpi_uint_cond_assign( size_t n,
+ mbedtls_mpi_uint *dest,
+ const mbedtls_mpi_uint *src,
+ unsigned char condition )
+{
+ size_t i;
+
+ /* MSVC has a warning about unary minus on unsigned integer types,
+ * but this is well-defined and precisely what we want to do here. */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+
+ /* all-bits 1 if condition is 1, all-bits 0 if condition is 0 */
+ const mbedtls_mpi_uint mask = -condition;
+
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+
+ for( i = 0; i < n; i++ )
+ dest[i] = ( src[i] & mask ) | ( dest[i] & ~mask );
+}
+
+#endif /* MBEDTLS_BIGNUM_C */
+
+#if defined(MBEDTLS_BASE64_C)
+
+unsigned char mbedtls_ct_base64_enc_char( unsigned char value )
+{
+ unsigned char digit = 0;
+ /* For each range of values, if value is in that range, mask digit with
+ * the corresponding value. Since value can only be in a single range,
+ * only at most one masking will change digit. */
+ digit |= mbedtls_ct_uchar_mask_of_range( 0, 25, value ) & ( 'A' + value );
+ digit |= mbedtls_ct_uchar_mask_of_range( 26, 51, value ) & ( 'a' + value - 26 );
+ digit |= mbedtls_ct_uchar_mask_of_range( 52, 61, value ) & ( '0' + value - 52 );
+ digit |= mbedtls_ct_uchar_mask_of_range( 62, 62, value ) & '+';
+ digit |= mbedtls_ct_uchar_mask_of_range( 63, 63, value ) & '/';
+ return( digit );
+}
+
+signed char mbedtls_ct_base64_dec_value( unsigned char c )
+{
+ unsigned char val = 0;
+ /* For each range of digits, if c is in that range, mask val with
+ * the corresponding value. Since c can only be in a single range,
+ * only at most one masking will change val. Set val to one plus
+ * the desired value so that it stays 0 if c is in none of the ranges. */
+ val |= mbedtls_ct_uchar_mask_of_range( 'A', 'Z', c ) & ( c - 'A' + 0 + 1 );
+ val |= mbedtls_ct_uchar_mask_of_range( 'a', 'z', c ) & ( c - 'a' + 26 + 1 );
+ val |= mbedtls_ct_uchar_mask_of_range( '0', '9', c ) & ( c - '0' + 52 + 1 );
+ val |= mbedtls_ct_uchar_mask_of_range( '+', '+', c ) & ( c - '+' + 62 + 1 );
+ val |= mbedtls_ct_uchar_mask_of_range( '/', '/', c ) & ( c - '/' + 63 + 1 );
+ /* At this point, val is 0 if c is an invalid digit and v+1 if c is
+ * a digit with the value v. */
+ return( val - 1 );
+}
+
+#endif /* MBEDTLS_BASE64_C */
+
+#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
+
+/** Shift some data towards the left inside a buffer.
+ *
+ * `mbedtls_ct_mem_move_to_left(start, total, offset)` is functionally
+ * equivalent to
+ * ```
+ * memmove(start, start + offset, total - offset);
+ * memset(start + offset, 0, total - offset);
+ * ```
+ * but it strives to use a memory access pattern (and thus total timing)
+ * that does not depend on \p offset. This timing independence comes at
+ * the expense of performance.
+ *
+ * \param start Pointer to the start of the buffer.
+ * \param total Total size of the buffer.
+ * \param offset Offset from which to copy \p total - \p offset bytes.
+ */
+static void mbedtls_ct_mem_move_to_left( void *start,
+ size_t total,
+ size_t offset )
+{
+ volatile unsigned char *buf = start;
+ size_t i, n;
+ if( total == 0 )
+ return;
+ for( i = 0; i < total; i++ )
+ {
+ unsigned no_op = mbedtls_ct_size_gt( total - offset, i );
+ /* The first `total - offset` passes are a no-op. The last
+ * `offset` passes shift the data one byte to the left and
+ * zero out the last byte. */
+ for( n = 0; n < total - 1; n++ )
+ {
+ unsigned char current = buf[n];
+ unsigned char next = buf[n+1];
+ buf[n] = mbedtls_ct_uint_if( no_op, current, next );
+ }
+ buf[total-1] = mbedtls_ct_uint_if( no_op, buf[total-1], 0 );
+ }
+}
+
+#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */
+
+#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)
+
+void mbedtls_ct_memcpy_if_eq( unsigned char *dest,
+ const unsigned char *src,
+ size_t len,
+ size_t c1,
+ size_t c2 )
+{
+ /* mask = c1 == c2 ? 0xff : 0x00 */
+ const size_t equal = mbedtls_ct_size_bool_eq( c1, c2 );
+ const unsigned char mask = (unsigned char) mbedtls_ct_size_mask( equal );
+
+ /* dest[i] = c1 == c2 ? src[i] : dest[i] */
+ for( size_t i = 0; i < len; i++ )
+ dest[i] = ( src[i] & mask ) | ( dest[i] & ~mask );
+}
+
+void mbedtls_ct_memcpy_offset( unsigned char *dest,
+ const unsigned char *src,
+ size_t offset,
+ size_t offset_min,
+ size_t offset_max,
+ size_t len )
+{
+ size_t offsetval;
+
+ for( offsetval = offset_min; offsetval <= offset_max; offsetval++ )
+ {
+ mbedtls_ct_memcpy_if_eq( dest, src + offsetval, len,
+ offsetval, offset );
+ }
+}
+
+int mbedtls_ct_hmac( mbedtls_md_context_t *ctx,
+ const unsigned char *add_data,
+ size_t add_data_len,
+ const unsigned char *data,
+ size_t data_len_secret,
+ size_t min_data_len,
+ size_t max_data_len,
+ unsigned char *output )
+{
+ /*
+ * This function breaks the HMAC abstraction and uses the md_clone()
+ * extension to the MD API in order to get constant-flow behaviour.
+ *
+ * HMAC(msg) is defined as HASH(okey + HASH(ikey + msg)) where + means
+ * concatenation, and okey/ikey are the XOR of the key with some fixed bit
+ * patterns (see RFC 2104, sec. 2), which are stored in ctx->hmac_ctx.
+ *
+ * We'll first compute inner_hash = HASH(ikey + msg) by hashing up to
+ * minlen, then cloning the context, and for each byte up to maxlen
+ * finishing up the hash computation, keeping only the correct result.
+ *
+ * Then we only need to compute HASH(okey + inner_hash) and we're done.
+ */
+ const mbedtls_md_type_t md_alg = mbedtls_md_get_type( ctx->md_info );
+ /* TLS 1.0-1.2 only support SHA-384, SHA-256, SHA-1, MD-5,
+ * all of which have the same block size except SHA-384. */
+ const size_t block_size = md_alg == MBEDTLS_MD_SHA384 ? 128 : 64;
+ const unsigned char * const ikey = ctx->hmac_ctx;
+ const unsigned char * const okey = ikey + block_size;
+ const size_t hash_size = mbedtls_md_get_size( ctx->md_info );
+
+ unsigned char aux_out[MBEDTLS_MD_MAX_SIZE];
+ mbedtls_md_context_t aux;
+ size_t offset;
+ int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+ mbedtls_md_init( &aux );
+
+#define MD_CHK( func_call ) \
+ do { \
+ ret = (func_call); \
+ if( ret != 0 ) \
+ goto cleanup; \
+ } while( 0 )
+
+ MD_CHK( mbedtls_md_setup( &aux, ctx->md_info, 0 ) );
+
+ /* After hmac_start() of hmac_reset(), ikey has already been hashed,
+ * so we can start directly with the message */
+ MD_CHK( mbedtls_md_update( ctx, add_data, add_data_len ) );
+ MD_CHK( mbedtls_md_update( ctx, data, min_data_len ) );
+
+ /* Fill the hash buffer in advance with something that is
+ * not a valid hash (barring an attack on the hash and
+ * deliberately-crafted input), in case the caller doesn't
+ * check the return status properly. */
+ memset( output, '!', hash_size );
+
+ /* For each possible length, compute the hash up to that point */
+ for( offset = min_data_len; offset <= max_data_len; offset++ )
+ {
+ MD_CHK( mbedtls_md_clone( &aux, ctx ) );
+ MD_CHK( mbedtls_md_finish( &aux, aux_out ) );
+ /* Keep only the correct inner_hash in the output buffer */
+ mbedtls_ct_memcpy_if_eq( output, aux_out, hash_size,
+ offset, data_len_secret );
+
+ if( offset < max_data_len )
+ MD_CHK( mbedtls_md_update( ctx, data + offset, 1 ) );
+ }
+
+ /* The context needs to finish() before it starts() again */
+ MD_CHK( mbedtls_md_finish( ctx, aux_out ) );
+
+ /* Now compute HASH(okey + inner_hash) */
+ MD_CHK( mbedtls_md_starts( ctx ) );
+ MD_CHK( mbedtls_md_update( ctx, okey, block_size ) );
+ MD_CHK( mbedtls_md_update( ctx, output, hash_size ) );
+ MD_CHK( mbedtls_md_finish( ctx, output ) );
+
+ /* Done, get ready for next time */
+ MD_CHK( mbedtls_md_hmac_reset( ctx ) );
+
+#undef MD_CHK
+
+cleanup:
+ mbedtls_md_free( &aux );
+ return( ret );
+}
+
+#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
+
+#if defined(MBEDTLS_BIGNUM_C)
+
+#define MPI_VALIDATE_RET( cond ) \
+ MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_MPI_BAD_INPUT_DATA )
+
+/*
+ * Conditionally assign X = Y, without leaking information
+ * about whether the assignment was made or not.
+ * (Leaking information about the respective sizes of X and Y is ok however.)
+ */
+#if defined(_MSC_VER) && defined(_M_ARM64) && (_MSC_FULL_VER < 193131103)
+/*
+ * MSVC miscompiles this function if it's inlined prior to Visual Studio 2022 version 17.1. See:
+ * https://developercommunity.visualstudio.com/t/c-compiler-miscompiles-part-of-mbedtls-library-on/1646989
+ */
+__declspec(noinline)
+#endif
+int mbedtls_mpi_safe_cond_assign( mbedtls_mpi *X,
+ const mbedtls_mpi *Y,
+ unsigned char assign )
+{
+ int ret = 0;
+ size_t i;
+ mbedtls_mpi_uint limb_mask;
+ MPI_VALIDATE_RET( X != NULL );
+ MPI_VALIDATE_RET( Y != NULL );
+
+ /* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */
+ limb_mask = mbedtls_ct_mpi_uint_mask( assign );;
+
+ MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
+
+ X->s = mbedtls_ct_cond_select_sign( assign, Y->s, X->s );
+
+ mbedtls_ct_mpi_uint_cond_assign( Y->n, X->p, Y->p, assign );
+
+ for( i = Y->n; i < X->n; i++ )
+ X->p[i] &= ~limb_mask;
+
+cleanup:
+ return( ret );
+}
+
+/*
+ * Conditionally swap X and Y, without leaking information
+ * about whether the swap was made or not.
+ * Here it is not ok to simply swap the pointers, which would lead to
+ * different memory access patterns when X and Y are used afterwards.
+ */
+int mbedtls_mpi_safe_cond_swap( mbedtls_mpi *X,
+ mbedtls_mpi *Y,
+ unsigned char swap )
+{
+ int ret, s;
+ size_t i;
+ mbedtls_mpi_uint limb_mask;
+ mbedtls_mpi_uint tmp;
+ MPI_VALIDATE_RET( X != NULL );
+ MPI_VALIDATE_RET( Y != NULL );
+
+ if( X == Y )
+ return( 0 );
+
+ /* all-bits 1 if swap is 1, all-bits 0 if swap is 0 */
+ limb_mask = mbedtls_ct_mpi_uint_mask( swap );
+
+ MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, Y->n ) );
+ MBEDTLS_MPI_CHK( mbedtls_mpi_grow( Y, X->n ) );
+
+ s = X->s;
+ X->s = mbedtls_ct_cond_select_sign( swap, Y->s, X->s );
+ Y->s = mbedtls_ct_cond_select_sign( swap, s, Y->s );
+
+
+ for( i = 0; i < X->n; i++ )
+ {
+ tmp = X->p[i];
+ X->p[i] = ( X->p[i] & ~limb_mask ) | ( Y->p[i] & limb_mask );
+ Y->p[i] = ( Y->p[i] & ~limb_mask ) | ( tmp & limb_mask );
+ }
+
+cleanup:
+ return( ret );
+}
+
+/*
+ * Compare signed values in constant time
+ */
+int mbedtls_mpi_lt_mpi_ct( const mbedtls_mpi *X,
+ const mbedtls_mpi *Y,
+ unsigned *ret )
+{
+ size_t i;
+ /* The value of any of these variables is either 0 or 1 at all times. */
+ unsigned cond, done, X_is_negative, Y_is_negative;
+
+ MPI_VALIDATE_RET( X != NULL );
+ MPI_VALIDATE_RET( Y != NULL );
+ MPI_VALIDATE_RET( ret != NULL );
+
+ if( X->n != Y->n )
+ return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
+
+ /*
+ * Set sign_N to 1 if N >= 0, 0 if N < 0.
+ * We know that N->s == 1 if N >= 0 and N->s == -1 if N < 0.
+ */
+ X_is_negative = ( X->s & 2 ) >> 1;
+ Y_is_negative = ( Y->s & 2 ) >> 1;
+
+ /*
+ * If the signs are different, then the positive operand is the bigger.
+ * That is if X is negative (X_is_negative == 1), then X < Y is true and it
+ * is false if X is positive (X_is_negative == 0).
+ */
+ cond = ( X_is_negative ^ Y_is_negative );
+ *ret = cond & X_is_negative;
+
+ /*
+ * This is a constant-time function. We might have the result, but we still
+ * need to go through the loop. Record if we have the result already.
+ */
+ done = cond;
+
+ for( i = X->n; i > 0; i-- )
+ {
+ /*
+ * If Y->p[i - 1] < X->p[i - 1] then X < Y is true if and only if both
+ * X and Y are negative.
+ *
+ * Again even if we can make a decision, we just mark the result and
+ * the fact that we are done and continue looping.
+ */
+ cond = mbedtls_ct_mpi_uint_lt( Y->p[i - 1], X->p[i - 1] );
+ *ret |= cond & ( 1 - done ) & X_is_negative;
+ done |= cond;
+
+ /*
+ * If X->p[i - 1] < Y->p[i - 1] then X < Y is true if and only if both
+ * X and Y are positive.
+ *
+ * Again even if we can make a decision, we just mark the result and
+ * the fact that we are done and continue looping.
+ */
+ cond = mbedtls_ct_mpi_uint_lt( X->p[i - 1], Y->p[i - 1] );
+ *ret |= cond & ( 1 - done ) & ( 1 - X_is_negative );
+ done |= cond;
+ }
+
+ return( 0 );
+}
+
+#endif /* MBEDTLS_BIGNUM_C */
+
+#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)
+
+int mbedtls_ct_rsaes_pkcs1_v15_unpadding( int mode,
+ unsigned char *input,
+ size_t ilen,
+ unsigned char *output,
+ size_t output_max_len,
+ size_t *olen )
+{
+ int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+ size_t i, plaintext_max_size;
+
+ /* The following variables take sensitive values: their value must
+ * not leak into the observable behavior of the function other than
+ * the designated outputs (output, olen, return value). Otherwise
+ * this would open the execution of the function to
+ * side-channel-based variants of the Bleichenbacher padding oracle
+ * attack. Potential side channels include overall timing, memory
+ * access patterns (especially visible to an adversary who has access
+ * to a shared memory cache), and branches (especially visible to
+ * an adversary who has access to a shared code cache or to a shared
+ * branch predictor). */
+ size_t pad_count = 0;
+ unsigned bad = 0;
+ unsigned char pad_done = 0;
+ size_t plaintext_size = 0;
+ unsigned output_too_large;
+
+ plaintext_max_size = ( output_max_len > ilen - 11 ) ? ilen - 11
+ : output_max_len;
+
+ /* Check and get padding length in constant time and constant
+ * memory trace. The first byte must be 0. */
+ bad |= input[0];
+
+ if( mode == MBEDTLS_RSA_PRIVATE )
+ {
+ /* Decode EME-PKCS1-v1_5 padding: 0x00 || 0x02 || PS || 0x00
+ * where PS must be at least 8 nonzero bytes. */
+ bad |= input[1] ^ MBEDTLS_RSA_CRYPT;
+
+ /* Read the whole buffer. Set pad_done to nonzero if we find
+ * the 0x00 byte and remember the padding length in pad_count. */
+ for( i = 2; i < ilen; i++ )
+ {
+ pad_done |= ((input[i] | (unsigned char)-input[i]) >> 7) ^ 1;
+ pad_count += ((pad_done | (unsigned char)-pad_done) >> 7) ^ 1;
+ }
+ }
+ else
+ {
+ /* Decode EMSA-PKCS1-v1_5 padding: 0x00 || 0x01 || PS || 0x00
+ * where PS must be at least 8 bytes with the value 0xFF. */
+ bad |= input[1] ^ MBEDTLS_RSA_SIGN;
+
+ /* Read the whole buffer. Set pad_done to nonzero if we find
+ * the 0x00 byte and remember the padding length in pad_count.
+ * If there's a non-0xff byte in the padding, the padding is bad. */
+ for( i = 2; i < ilen; i++ )
+ {
+ pad_done |= mbedtls_ct_uint_if( input[i], 0, 1 );
+ pad_count += mbedtls_ct_uint_if( pad_done, 0, 1 );
+ bad |= mbedtls_ct_uint_if( pad_done, 0, input[i] ^ 0xFF );
+ }
+ }
+
+ /* If pad_done is still zero, there's no data, only unfinished padding. */
+ bad |= mbedtls_ct_uint_if( pad_done, 0, 1 );
+
+ /* There must be at least 8 bytes of padding. */
+ bad |= mbedtls_ct_size_gt( 8, pad_count );
+
+ /* If the padding is valid, set plaintext_size to the number of
+ * remaining bytes after stripping the padding. If the padding
+ * is invalid, avoid leaking this fact through the size of the
+ * output: use the maximum message size that fits in the output
+ * buffer. Do it without branches to avoid leaking the padding
+ * validity through timing. RSA keys are small enough that all the
+ * size_t values involved fit in unsigned int. */
+ plaintext_size = mbedtls_ct_uint_if(
+ bad, (unsigned) plaintext_max_size,
+ (unsigned) ( ilen - pad_count - 3 ) );
+
+ /* Set output_too_large to 0 if the plaintext fits in the output
+ * buffer and to 1 otherwise. */
+ output_too_large = mbedtls_ct_size_gt( plaintext_size,
+ plaintext_max_size );
+
+ /* Set ret without branches to avoid timing attacks. Return:
+ * - INVALID_PADDING if the padding is bad (bad != 0).
+ * - OUTPUT_TOO_LARGE if the padding is good but the decrypted
+ * plaintext does not fit in the output buffer.
+ * - 0 if the padding is correct. */
+ ret = - (int) mbedtls_ct_uint_if(
+ bad, - MBEDTLS_ERR_RSA_INVALID_PADDING,
+ mbedtls_ct_uint_if( output_too_large,
+ - MBEDTLS_ERR_RSA_OUTPUT_TOO_LARGE,
+ 0 ) );
+
+ /* If the padding is bad or the plaintext is too large, zero the
+ * data that we're about to copy to the output buffer.
+ * We need to copy the same amount of data
+ * from the same buffer whether the padding is good or not to
+ * avoid leaking the padding validity through overall timing or
+ * through memory or cache access patterns. */
+ bad = mbedtls_ct_uint_mask( bad | output_too_large );
+ for( i = 11; i < ilen; i++ )
+ input[i] &= ~bad;
+
+ /* If the plaintext is too large, truncate it to the buffer size.
+ * Copy anyway to avoid revealing the length through timing, because
+ * revealing the length is as bad as revealing the padding validity
+ * for a Bleichenbacher attack. */
+ plaintext_size = mbedtls_ct_uint_if( output_too_large,
+ (unsigned) plaintext_max_size,
+ (unsigned) plaintext_size );
+
+ /* Move the plaintext to the leftmost position where it can start in
+ * the working buffer, i.e. make it start plaintext_max_size from
+ * the end of the buffer. Do this with a memory access trace that
+ * does not depend on the plaintext size. After this move, the
+ * starting location of the plaintext is no longer sensitive
+ * information. */
+ mbedtls_ct_mem_move_to_left( input + ilen - plaintext_max_size,
+ plaintext_max_size,
+ plaintext_max_size - plaintext_size );
+
+ /* Finally copy the decrypted plaintext plus trailing zeros into the output
+ * buffer. If output_max_len is 0, then output may be an invalid pointer
+ * and the result of memcpy() would be undefined; prevent undefined
+ * behavior making sure to depend only on output_max_len (the size of the
+ * user-provided output buffer), which is independent from plaintext
+ * length, validity of padding, success of the decryption, and other
+ * secrets. */
+ if( output_max_len != 0 )
+ memcpy( output, input + ilen - plaintext_max_size, plaintext_max_size );
+
+ /* Report the amount of data we copied to the output buffer. In case
+ * of errors (bad padding or output too large), the value of *olen
+ * when this function returns is not specified. Making it equivalent
+ * to the good case limits the risks of leaking the padding validity. */
+ *olen = plaintext_size;
+
+ return( ret );
+}
+
+#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */