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Evolve mbedtls_ct_uchar_in_range_if interface

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman 2023-05-09 10:39:03 +01:00
parent 0ee9683987
commit 8c94e219f9
2 changed files with 29 additions and 15 deletions
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20
library/base64.c
View file

@ -40,11 +40,11 @@ unsigned char mbedtls_ct_base64_enc_char(unsigned char value)
/* 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) & '/';
digit |= mbedtls_ct_uchar_in_range_if(0, 25, value, 'A' + value);
digit |= mbedtls_ct_uchar_in_range_if(26, 51, value, 'a' + value - 26);
digit |= mbedtls_ct_uchar_in_range_if(52, 61, value, '0' + value - 52);
digit |= mbedtls_ct_uchar_in_range_if(62, 62, value, '+');
digit |= mbedtls_ct_uchar_in_range_if(63, 63, value, '/');
return digit;
}
@ -56,11 +56,11 @@ signed char mbedtls_ct_base64_dec_value(unsigned char c)
* 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);
val |= mbedtls_ct_uchar_in_range_if('A', 'Z', c, c - 'A' + 0 + 1);
val |= mbedtls_ct_uchar_in_range_if('a', 'z', c, c - 'a' + 26 + 1);
val |= mbedtls_ct_uchar_in_range_if('0', '9', c, c - '0' + 52 + 1);
val |= mbedtls_ct_uchar_in_range_if('+', '+', c, c - '+' + 62 + 1);
val |= mbedtls_ct_uchar_in_range_if('/', '/', 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;

24
library/constant_time_internal.h
View file

@ -333,13 +333,27 @@ int mbedtls_ct_rsaes_pkcs1_v15_unpadding(unsigned char *input,
#if defined(MBEDTLS_BASE64_C)
/* Return 0xff if low <= c <= high, 0 otherwise.
/** Constant-flow char selection
*
* Constant flow with respect to c.
* \param low Bottom of range
* \param high Top of range
* \param c Value to compare to range
* \param t Value to return, if in range
*
* \return \p t if \p low <= \p c <= \p high, 0 otherwise.
*/
unsigned char mbedtls_ct_uchar_mask_of_range(unsigned char low,
unsigned char high,
unsigned char c);
static inline unsigned char mbedtls_ct_uchar_in_range_if(unsigned char low,
unsigned char high,
unsigned char c,
unsigned char t)
{
/* 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 (unsigned char)
mbedtls_ct_uint_if(~mbedtls_ct_mpi_uint_mask(low_mask | high_mask), t, 0);
}
#endif /* MBEDTLS_BASE64_C */