| /** |
| * 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 <stddef.h> |
| |
| |
| /** 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 ); |
| |
| #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_TLS_CBC) |
| |
| /** 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_TLS_CBC */ |
| |
| #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 */ |
