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Move mbedtls_ct_base64_dec_value function to the constant-time module

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Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
This commit is contained in:
Gabor Mezei 2021-11-15 16:22:37 +01:00
parent 9a4074aa1e
commit 358829abc9
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GPG key ID: 106F5A41ECC305BD
3 changed files with 30 additions and 29 deletions
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29
library/base64.c
View file

@ -109,35 +109,6 @@ int mbedtls_base64_encode( unsigned char *dst, size_t dlen, size_t *olen,
return( 0 );
}
/* 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).
*
* The implementation is constant-flow (no branch or memory access depending
* on the value of c) unless the compiler inlines and optimizes a specific
* access.
*/
MBEDTLS_STATIC_TESTABLE
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 );
}
/*
* Decode a base64-formatted buffer
*/

28
library/constant_time.c
View file

@ -344,6 +344,34 @@ unsigned char mbedtls_ct_base64_enc_char( unsigned char val )
return( digit );
}
/* 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).
*
* The implementation is constant-flow (no branch or memory access depending
* on the value of c) unless the compiler inlines and optimizes a specific
* access.
*/
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)

2
library/constant_time_internal.h
View file

@ -171,6 +171,8 @@ void mbedtls_ct_mpi_uint_cond_assign( size_t n,
unsigned char mbedtls_ct_base64_enc_char( unsigned char val );
signed char mbedtls_ct_base64_dec_value( unsigned char c );
#endif /* MBEDTLS_BASE64_C */
#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC)