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Fix ASN1 bitstring writing

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Refactor the function mbedtls_asn1_write_bitstring() that removes
trailing 0s at the end of DER encoded bitstrings. The function is
implemented according to Hanno Becker's suggestions.

This commit also changes the functions x509write_crt_set_ns_cert_type
and crt_set_key_usage to call the new function as the use named
bitstrings instead of the regular bitstrings.
This commit is contained in:
Andres Amaya Garcia 2018-09-26 10:48:24 +01:00
parent 6f76795bf5
commit d60e378016
3 changed files with 87 additions and 22 deletions
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28
library/asn1write.c
View file

@ -294,22 +294,28 @@ int mbedtls_asn1_write_bitstring( unsigned char **p, unsigned char *start,
const unsigned char *buf, size_t bits )
{
int ret;
size_t len = 0, size;
size_t len = 0;
size_t unused_bits, byte_len;
size = ( bits / 8 ) + ( ( bits % 8 ) ? 1 : 0 );
byte_len = ( bits + 7 ) / 8;
unused_bits = ( byte_len * 8 ) - bits;
// Calculate byte length
//
if( *p < start || (size_t)( *p - start ) < size + 1 )
if( *p < start || (size_t)( *p - start ) < byte_len + 1 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
len = size + 1;
(*p) -= size;
memcpy( *p, buf, size );
len = byte_len + 1;
// Write unused bits
//
*--(*p) = (unsigned char) (size * 8 - bits);
/* Write the bitstring. Ensure the unused bits are zeroed */
if( byte_len > 0 )
{
byte_len--;
*--( *p ) = buf[byte_len] & ~( ( 0x1 << unused_bits ) - 1 );
( *p ) -= byte_len;
memcpy( *p, buf, byte_len );
}
/* Write unused bits */
*--( *p ) = (unsigned char)unused_bits;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_BIT_STRING ) );

45
library/x509write_crt.c
View file

@ -218,26 +218,51 @@ int mbedtls_x509write_crt_set_authority_key_identifier( mbedtls_x509write_cert *
}
#endif /* MBEDTLS_SHA1_C */
static size_t crt_get_unused_bits_for_named_bitstring( unsigned char bitstring,
size_t bit_offset )
{
size_t unused_bits;
/* Count the unused bits removing trailing 0s */
for( unused_bits = bit_offset; unused_bits < 8; unused_bits++ )
if( ( ( bitstring >> unused_bits ) & 0x1 ) != 0 )
break;
return( unused_bits );
}
int mbedtls_x509write_crt_set_key_usage( mbedtls_x509write_cert *ctx,
unsigned int key_usage )
{
unsigned char buf[4], ku;
unsigned char *c;
int ret;
size_t unused_bits;
const unsigned int allowed_bits = MBEDTLS_X509_KU_DIGITAL_SIGNATURE |
MBEDTLS_X509_KU_NON_REPUDIATION |
MBEDTLS_X509_KU_KEY_ENCIPHERMENT |
MBEDTLS_X509_KU_DATA_ENCIPHERMENT |
MBEDTLS_X509_KU_KEY_AGREEMENT |
MBEDTLS_X509_KU_KEY_CERT_SIGN |
MBEDTLS_X509_KU_CRL_SIGN;
/* We currently only support 7 bits, from 0x80 to 0x02 */
if( ( key_usage & ~0xfe ) != 0 )
/* Check that nothing other than the allowed flags is set */
if( ( key_usage & ~allowed_bits ) != 0 )
return( MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE );
c = buf + 4;
ku = (unsigned char) key_usage;
ku = (unsigned char)key_usage;
unused_bits = crt_get_unused_bits_for_named_bitstring( ku, 1 );
ret = mbedtls_asn1_write_bitstring( &c, buf, &ku, 8 - unused_bits );
if( ( ret = mbedtls_asn1_write_bitstring( &c, buf, &ku, 7 ) ) != 4 )
if( ret < 0 )
return( ret );
else if( ret < 3 || ret > 4 )
return( MBEDTLS_ERR_X509_INVALID_FORMAT );
ret = mbedtls_x509write_crt_set_extension( ctx, MBEDTLS_OID_KEY_USAGE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_KEY_USAGE ),
1, buf, 4 );
1, c, (size_t)ret );
if( ret != 0 )
return( ret );
@ -249,16 +274,22 @@ int mbedtls_x509write_crt_set_ns_cert_type( mbedtls_x509write_cert *ctx,
{
unsigned char buf[4];
unsigned char *c;
size_t unused_bits;
int ret;
c = buf + 4;
if( ( ret = mbedtls_asn1_write_bitstring( &c, buf, &ns_cert_type, 8 ) ) != 4 )
unused_bits = crt_get_unused_bits_for_named_bitstring( ns_cert_type, 0 );
ret = mbedtls_asn1_write_bitstring( &c,
buf,
&ns_cert_type,
8 - unused_bits );
if( ret < 3 || ret > 4 )
return( ret );
ret = mbedtls_x509write_crt_set_extension( ctx, MBEDTLS_OID_NS_CERT_TYPE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_NS_CERT_TYPE ),
0, buf, 4 );
0, c, (size_t)ret );
if( ret != 0 )
return( ret );

36
library/x509write_csr.c
View file

@ -81,20 +81,39 @@ int mbedtls_x509write_csr_set_extension( mbedtls_x509write_csr *ctx,
0, val, val_len );
}
static size_t csr_get_unused_bits_for_named_bitstring( unsigned char bitstring,
size_t bit_offset )
{
size_t unused_bits;
/* Count the unused bits removing trailing 0s */
for( unused_bits = bit_offset; unused_bits < 8; unused_bits++ )
if( ( ( bitstring >> unused_bits ) & 0x1 ) != 0 )
break;
return( unused_bits );
}
int mbedtls_x509write_csr_set_key_usage( mbedtls_x509write_csr *ctx, unsigned char key_usage )
{
unsigned char buf[4];
unsigned char *c;
size_t unused_bits;
int ret;
c = buf + 4;
if( ( ret = mbedtls_asn1_write_bitstring( &c, buf, &key_usage, 7 ) ) != 4 )
unused_bits = csr_get_unused_bits_for_named_bitstring( key_usage, 0 );
ret = mbedtls_asn1_write_bitstring( &c, buf, &key_usage, 8 - unused_bits );
if( ret < 0 )
return( ret );
else if( ret < 3 || ret > 4 )
return( MBEDTLS_ERR_X509_INVALID_FORMAT );
ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_KEY_USAGE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_KEY_USAGE ),
buf, 4 );
c, (size_t)ret );
if( ret != 0 )
return( ret );
@ -106,16 +125,25 @@ int mbedtls_x509write_csr_set_ns_cert_type( mbedtls_x509write_csr *ctx,
{
unsigned char buf[4];
unsigned char *c;
size_t unused_bits;
int ret;
c = buf + 4;
if( ( ret = mbedtls_asn1_write_bitstring( &c, buf, &ns_cert_type, 8 ) ) != 4 )
unused_bits = csr_get_unused_bits_for_named_bitstring( ns_cert_type, 0 );
ret = mbedtls_asn1_write_bitstring( &c,
buf,
&ns_cert_type,
8 - unused_bits );
if( ret < 0 )
return( ret );
else if( ret < 3 || ret > 4 )
return( ret );
ret = mbedtls_x509write_csr_set_extension( ctx, MBEDTLS_OID_NS_CERT_TYPE,
MBEDTLS_OID_SIZE( MBEDTLS_OID_NS_CERT_TYPE ),
buf, 4 );
c, (size_t)ret );
if( ret != 0 )
return( ret );