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cmac: clean up padding function and comments

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Manuel Pégourié-Gonnard 2016-01-13 13:14:04 +00:00 committed by Simon Butcher
parent 475f06f609
commit d2c3d3eddb
1 changed files with 13 additions and 19 deletions
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32
library/cmac.c
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@ -187,28 +187,26 @@ void mbedtls_cmac_free( mbedtls_cmac_context *ctx )
mbedtls_zeroize( ctx, sizeof( mbedtls_cmac_context ) );
}
/* TODO: Use cipher padding function? */
static void padding( const unsigned char *lastb,
unsigned char *pad,
const size_t length )
/*
* Create padded last block from (partial) last block.
*
* We can't use the padding option from the cipher layer, as it only works for
* CBC and we use ECB mode, and anyway we need to XOR K1 or K2 in addition.
*/
static void padding( unsigned char padded_block[16],
const unsigned char *last_block,
size_t length )
{
size_t j;
/* original last block */
for( j = 0; j < 16; j++ )
{
if( j < length )
{
pad[j] = lastb[j];
}
padded_block[j] = last_block[j];
else if( j == length )
{
pad[j] = 0x80;
}
padded_block[j] = 0x80;
else
{
pad[j] = 0x00;
}
padded_block[j] = 0x00;
}
}
@ -232,9 +230,6 @@ static int cmac_generate( mbedtls_cmac_context *ctx,
if( tag_len < 4 || tag_len > 16 || tag_len % 2 != 0 )
return( MBEDTLS_ERR_CMAC_BAD_INPUT );
/* TODO: Use cipher padding function? */
// mbedtls_cipher_set_padding_mode( ctx->cipher, MBEDTLS_PADDING_ONE_AND_ZEROS );
n = ( in_len + 15 ) / 16; /* n is number of rounds */
if( n == 0 )
@ -255,8 +250,7 @@ static int cmac_generate( mbedtls_cmac_context *ctx,
}
else
{
/* TODO: Use cipher padding function? */
padding( &input[16 * ( n - 1 )], padded, in_len % 16 );
padding( padded, &input[16 * ( n - 1 )], in_len % 16 );
XOR_128( padded, ctx->K2, M_last );
}