/** * 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. */ #ifndef MBEDTLS_CONSTANT_TIME_INTERNAL_H #define MBEDTLS_CONSTANT_TIME_INTERNAL_H #include "common.h" #if defined(MBEDTLS_BIGNUM_C) #include "mbedtls/bignum.h" #endif #if defined(MBEDTLS_SSL_TLS_C) #include "ssl_misc.h" #endif #include /** Turn a value into a mask: * - if \p value == 0, return the all-bits 0 mask, aka 0 * - otherwise, return the all-bits 1 mask, aka (unsigned) -1 * * This function can be used to write constant-time code by replacing branches * with bit operations using masks. * * \param value The value to analyze. * * \return Zero if \p value is zero, otherwise all-bits-one. */ unsigned mbedtls_ct_uint_mask( unsigned value ); #if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) /** Turn a value into a mask: * - if \p value == 0, return the all-bits 0 mask, aka 0 * - otherwise, return the all-bits 1 mask, aka (size_t) -1 * * This function can be used to write constant-time code by replacing branches * with bit operations using masks. * * \param value The value to analyze. * * \return Zero if \p value is zero, otherwise all-bits-one. */ size_t mbedtls_ct_size_mask( size_t value ); #endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */ #if defined(MBEDTLS_BIGNUM_C) /** Turn a value into a mask: * - if \p value == 0, return the all-bits 0 mask, aka 0 * - otherwise, return the all-bits 1 mask, aka (mbedtls_mpi_uint) -1 * * This function can be used to write constant-time code by replacing branches * with bit operations using masks. * * \param value The value to analyze. * * \return Zero if \p value is zero, otherwise all-bits-one. */ mbedtls_mpi_uint mbedtls_ct_mpi_uint_mask( mbedtls_mpi_uint value ); #endif /* MBEDTLS_BIGNUM_C */ #if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) /** Constant-flow mask generation for "greater or equal" 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 greater or equal than \p y, * otherwise zero. */ size_t mbedtls_ct_size_mask_ge( size_t x, size_t y ); #endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */ /** Constant-flow boolean "equal" 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 equals to \p y, otherwise 0. */ unsigned mbedtls_ct_size_bool_eq( size_t x, size_t y ); #if defined(MBEDTLS_BIGNUM_C) /** Decide if an integer is less than the other, without branches. * * 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 is less than \p y, otherwise 0. */ unsigned mbedtls_ct_mpi_uint_lt( const mbedtls_mpi_uint x, const mbedtls_mpi_uint y ); /** * \brief Check if one unsigned MPI is less than another in constant * time. * * \param A The left-hand MPI. This must point to an array of limbs * with the same allocated length as \p B. * \param B The right-hand MPI. This must point to an array of limbs * with the same allocated length as \p A. * \param limbs The number of limbs in \p A and \p B. * * \return The result of the comparison: * \c 1 if \p A is less than \p B. * \c 0 if \p A is greater than or equal to \p B. */ unsigned mbedtls_mpi_core_lt_ct( const mbedtls_mpi_uint *A, const mbedtls_mpi_uint *B, size_t limbs); #endif /* MBEDTLS_BIGNUM_C */ /** Choose between two integer values without branches. * * This is equivalent to `condition ? if1 : if0`, but is likely to be compiled * to code using bitwise operation rather than a branch. * * \param condition Condition to test. * \param if1 Value to use if \p condition is nonzero. * \param if0 Value to use if \p condition is zero. * * \return \c if1 if \p condition is nonzero, otherwise \c if0. */ unsigned mbedtls_ct_uint_if( unsigned condition, unsigned if1, unsigned if0 ); #if defined(MBEDTLS_BIGNUM_C) /** Conditionally assign a value without branches. * * This is equivalent to `if ( condition ) dest = src`, but is likely * to be compiled to code using bitwise operation rather than a branch. * * \param n \p dest and \p src must be arrays of limbs of size n. * \param dest The MPI to conditionally assign to. This must point * to an initialized MPI. * \param src The MPI to be assigned from. This must point to an * initialized MPI. * \param condition Condition to test, must be 0 or 1. */ void mbedtls_ct_mpi_uint_cond_assign( size_t n, mbedtls_mpi_uint *dest, const mbedtls_mpi_uint *src, unsigned char condition ); #endif /* MBEDTLS_BIGNUM_C */ #if defined(MBEDTLS_BASE64_C) /** Given a value in the range 0..63, return the corresponding Base64 digit. * * The implementation assumes that letters are consecutive (e.g. ASCII * but not EBCDIC). * * \param value A value in the range 0..63. * * \return A base64 digit converted from \p value. */ unsigned char mbedtls_ct_base64_enc_char( unsigned char value ); /** Given a Base64 digit, return its value. * * If c is not a Base64 digit ('A'..'Z', 'a'..'z', '0'..'9', '+' or '/'), * return -1. * * The implementation assumes that letters are consecutive (e.g. ASCII * but not EBCDIC). * * \param c A base64 digit. * * \return The value of the base64 digit \p c. */ signed char mbedtls_ct_base64_dec_value( unsigned char c ); #endif /* MBEDTLS_BASE64_C */ #if defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC) /** Conditional memcpy without branches. * * This is equivalent to `if ( c1 == c2 ) memcpy(dest, src, len)`, but is likely * to be compiled to code using bitwise operation rather than a branch. * * \param dest The pointer to conditionally copy to. * \param src The pointer to copy from. Shouldn't overlap with \p dest. * \param len The number of bytes to copy. * \param c1 The first value to analyze in the condition. * \param c2 The second value to analyze in the condition. */ void mbedtls_ct_memcpy_if_eq( unsigned char *dest, const unsigned char *src, size_t len, size_t c1, size_t c2 ); /** Copy data from a secret position with constant flow. * * This function copies \p len bytes from \p src_base + \p offset_secret to \p * dst, with a code flow and memory access pattern that does not depend on \p * offset_secret, but only on \p offset_min, \p offset_max and \p len. * Functionally equivalent to `memcpy(dst, src + offset_secret, len)`. * * \note This function reads from \p dest, but the value that * is read does not influence the result and this * function's behavior is well-defined regardless of the * contents of the buffers. This may result in false * positives from static or dynamic analyzers, especially * if \p dest is not initialized. * * \param dest The destination buffer. This must point to a writable * buffer of at least \p len bytes. * \param src The base of the source buffer. This must point to a * readable buffer of at least \p offset_max + \p len * bytes. Shouldn't overlap with \p dest. * \param offset The offset in the source buffer from which to copy. * This must be no less than \p offset_min and no greater * than \p offset_max. * \param offset_min The minimal value of \p offset. * \param offset_max The maximal value of \p offset. * \param len The number of bytes to copy. */ 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 ); /** Compute the HMAC of variable-length data with constant flow. * * This function computes the HMAC of the concatenation of \p add_data and \p * data, and does with a code flow and memory access pattern that does not * depend on \p data_len_secret, but only on \p min_data_len and \p * max_data_len. In particular, this function always reads exactly \p * max_data_len bytes from \p data. * * \param ctx The HMAC context. It must have keys configured * with mbedtls_md_hmac_starts() and use one of the * following hashes: SHA-384, SHA-256, SHA-1 or MD-5. * It is reset using mbedtls_md_hmac_reset() after * the computation is complete to prepare for the * next computation. * \param add_data The first part of the message whose HMAC is being * calculated. This must point to a readable buffer * of \p add_data_len bytes. * \param add_data_len The length of \p add_data in bytes. * \param data The buffer containing the second part of the * message. This must point to a readable buffer * of \p max_data_len bytes. * \param data_len_secret The length of the data to process in \p data. * This must be no less than \p min_data_len and no * greater than \p max_data_len. * \param min_data_len The minimal length of the second part of the * message, read from \p data. * \param max_data_len The maximal length of the second part of the * message, read from \p data. * \param output The HMAC will be written here. This must point to * a writable buffer of sufficient size to hold the * HMAC value. * * \retval 0 on success. * \retval #MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED * The hardware accelerator failed. */ #if defined(MBEDTLS_USE_PSA_CRYPTO) int mbedtls_ct_hmac( mbedtls_svc_key_id_t key, psa_algorithm_t alg, 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 ); #else 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 ); #endif /* MBEDTLS_USE_PSA_CRYPTO */ #endif /* MBEDTLS_SSL_SOME_SUITES_USE_MAC */ #if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) /** This function performs the unpadding part of a PKCS#1 v1.5 decryption * operation (EME-PKCS1-v1_5 decoding). * * \note The return value from this function is a sensitive value * (this is unusual). #MBEDTLS_ERR_RSA_OUTPUT_TOO_LARGE shouldn't happen * in a well-written application, but 0 vs #MBEDTLS_ERR_RSA_INVALID_PADDING * is often a situation that an attacker can provoke and leaking which * one is the result is precisely the information the attacker wants. * * \param input The input buffer which is the payload inside PKCS#1v1.5 * encryption padding, called the "encoded message EM" * by the terminology. * \param ilen The length of the payload in the \p input buffer. * \param output The buffer for the payload, called "message M" by the * PKCS#1 terminology. This must be a writable buffer of * length \p output_max_len bytes. * \param olen The address at which to store the length of * the payload. This must not be \c NULL. * \param output_max_len The length in bytes of the output buffer \p output. * * \return \c 0 on success. * \return #MBEDTLS_ERR_RSA_OUTPUT_TOO_LARGE * The output buffer is too small for the unpadded payload. * \return #MBEDTLS_ERR_RSA_INVALID_PADDING * The input doesn't contain properly formatted padding. */ int mbedtls_ct_rsaes_pkcs1_v15_unpadding( unsigned char *input, size_t ilen, unsigned char *output, size_t output_max_len, size_t *olen ); #endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */ #endif /* MBEDTLS_CONSTANT_TIME_INTERNAL_H */