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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
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@ -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 ) );