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cmac: some more padding-related tune-ups

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- use one less temporary buffer
- pedantic: in_len + 15 was a potential overflow
- use a more explicit name instead of 'flag'
- Mn was a bit misleading
This commit is contained in:
Manuel Pégourié-Gonnard 2016-01-13 14:27:55 +00:00 committed by Simon Butcher
parent da8724fbc6
commit 59ae4bad18
1 changed files with 22 additions and 29 deletions
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51
library/cmac.c
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@ -54,19 +54,20 @@
/* /*
* XOR 128-bit * XOR 128-bit
*/ */
#define XOR_128( i1, i2, o ) \ #define XOR_128( o, i1, i2 ) \
for( i = 0; i < 16; i++ ) \ for( i = 0; i < 16; i++ ) \
( o )[i] = ( i1 )[i] ^ ( i2 )[i]; ( o )[i] = ( i1 )[i] ^ ( i2 )[i];
/* /*
* Update the CMAC state in Mn using an input block x * Update the CMAC state using an input block x
* TODO: Compiler optimisation
*/ */
#define UPDATE_CMAC( x ) \ #define UPDATE_CMAC( x ) \
XOR_128( Mn, ( x ), Mn ); \ do { \
XOR_128( state, ( x ), state ); \
if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, \ if( ( ret = mbedtls_cipher_update( &ctx->cipher_ctx, \
Mn, 16, Mn, &olen ) ) != 0 ) \ state, 16, state, &olen ) ) != 0 ) \
return( ret ); return( ret ); \
} while( 0 )
/* Implementation that should never be optimized out by the compiler */ /* Implementation that should never be optimized out by the compiler */
static void mbedtls_zeroize( void *v, size_t n ) { static void mbedtls_zeroize( void *v, size_t n ) {
@ -217,10 +218,9 @@ static int cmac_generate( mbedtls_cmac_context *ctx,
const unsigned char *input, size_t in_len, const unsigned char *input, size_t in_len,
unsigned char *tag, size_t tag_len ) unsigned char *tag, size_t tag_len )
{ {
unsigned char Mn[16]; unsigned char state[16];
unsigned char M_last[16]; unsigned char M_last[16];
unsigned char padded[16]; int n, i, j, ret, needs_padding;
int n, i, j, ret, flag;
size_t olen; size_t olen;
/* /*
@ -230,40 +230,33 @@ static int cmac_generate( mbedtls_cmac_context *ctx,
if( tag_len < 4 || tag_len > 16 || tag_len % 2 != 0 ) if( tag_len < 4 || tag_len > 16 || tag_len % 2 != 0 )
return( MBEDTLS_ERR_CMAC_BAD_INPUT ); return( MBEDTLS_ERR_CMAC_BAD_INPUT );
n = ( in_len + 15 ) / 16; /* n is number of rounds */ if( in_len == 0 )
needs_padding = 1;
if( n == 0 )
{
n = 1;
flag = 0;
}
else else
{ needs_padding = in_len % 16 != 0;
flag = ( ( in_len % 16 ) == 0);
} n = in_len / 16 + needs_padding;
/* Calculate last block */ /* Calculate last block */
if( flag ) if( needs_padding )
{ {
/* Last block is complete block */ padding( M_last, input + 16 * ( n - 1 ), in_len % 16 );
XOR_128( &input[16 * ( n - 1 )], ctx->K1, M_last ); XOR_128( M_last, M_last, ctx->K2 );
} }
else else
{ {
padding( padded, &input[16 * ( n - 1 )], in_len % 16 ); /* Last block is complete block */
XOR_128( padded, ctx->K2, M_last ); XOR_128( M_last, input + 16 * ( n - 1 ), ctx->K1 );
} }
memset( Mn, 0, 16 ); memset( state, 0, 16 );
for( j = 0; j < n - 1; j++ ) for( j = 0; j < n - 1; j++ )
{ UPDATE_CMAC( input + 16 * j );
UPDATE_CMAC( &input[16 * j] );
}
UPDATE_CMAC( M_last ); UPDATE_CMAC( M_last );
memcpy( tag, Mn, 16 ); memcpy( tag, state, 16 );
return( 0 ); return( 0 );
} }