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/**
* Constant-time functions
*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
*/
#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 "mbedtls/ssl_internal.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_MODES_USE_MAC) || defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) || \
defined(MBEDTLS_NIST_KW_C) || defined(MBEDTLS_CIPHER_MODE_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 /* defined(MBEDTLS_SSL_SOME_MODES_USE_MAC) || defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) ||
defined(MBEDTLS_NIST_KW_C) || defined(MBEDTLS_CIPHER_MODE_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) || defined(MBEDTLS_NIST_KW_C) || \
defined(MBEDTLS_CIPHER_MODE_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 /* defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) || defined(MBEDTLS_NIST_KW_C) ||
defined(MBEDTLS_CIPHER_MODE_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_MODES_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.
*/
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_SSL_SOME_MODES_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 mode The mode of operation. This must be either
* #MBEDTLS_RSA_PRIVATE or #MBEDTLS_RSA_PUBLIC (deprecated).
* \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(int mode,
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 */
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