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Make get_one_and_zeros_padding() constant-time

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This commit is contained in:
Manuel Pégourié-Gonnard 2013-10-27 18:25:03 +01:00
parent d17df51277
commit 6c32990114
1 changed files with 12 additions and 8 deletions
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20
library/cipher.c
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@ -456,20 +456,24 @@ static void add_one_and_zeros_padding( unsigned char *output,
static int get_one_and_zeros_padding( unsigned char *input, size_t input_len,
size_t *data_len )
{
unsigned char *p = input + input_len - 1;
size_t i;
unsigned char done = 0, prev_done, bad;
if( NULL == input || NULL == data_len )
return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
while( *p == 0x00 && p > input )
--p;
bad = 0xFF;
*data_len = 0;
for( i = input_len; i > 0; i-- )
{
prev_done = done;
done |= ( input[i-1] != 0 );
*data_len |= ( i - 1 ) * ( done != prev_done );
bad &= ( input[i-1] ^ 0x80 ) | ( done == prev_done );
}
if( *p != 0x80 )
return POLARSSL_ERR_CIPHER_INVALID_PADDING;
return POLARSSL_ERR_CIPHER_INVALID_PADDING * (bad != 0);
*data_len = p - input;
return 0;
}
#endif /* POLARSSL_CIPHER_PADDING_ONE_AND_ZEROS */