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Work around compressed EC public key in some cases

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This commit is contained in:
Manuel Pégourié-Gonnard 2014-03-19 16:18:38 +01:00
parent eab20d2a9c
commit 5246ee5c59
3 changed files with 46 additions and 50 deletions
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6
include/polarssl/ecp.h
View File

@ -376,8 +376,10 @@ int ecp_point_write_binary( const ecp_group *grp, const ecp_point *P,
* \param ilen Actual length of input
*
* \return 0 if successful,
* POLARSSL_ERR_ECP_BAD_INPUT_DATA if input is invalid
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
* POLARSSL_ERR_ECP_BAD_INPUT_DATA if input is invalid,
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed,
* POLARSSL_ERR_ECP_FEATURE_UNAVAILABLE if the point format
* is not implemented.
*
* \note This function does NOT check that the point actually
* belongs to the given group, see ecp_check_pubkey() for

8
library/ecp.c
View File

@ -478,7 +478,8 @@ cleanup:
* Import a point from unsigned binary data (SEC1 2.3.4)
*/
int ecp_point_read_binary( const ecp_group *grp, ecp_point *pt,
const unsigned char *buf, size_t ilen ) {
const unsigned char *buf, size_t ilen )
{
int ret;
size_t plen;
@ -487,7 +488,10 @@ int ecp_point_read_binary( const ecp_group *grp, ecp_point *pt,
plen = mpi_size( &grp->P );
if( ilen != 2 * plen + 1 || buf[0] != 0x04 )
if( buf[0] != 0x04 )
return( POLARSSL_ERR_ECP_FEATURE_UNAVAILABLE );
if( ilen != 2 * plen + 1 )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
MPI_CHK( mpi_read_binary( &pt->X, buf + 1, plen ) );

82
library/pkparse.c
View File

@ -185,43 +185,6 @@ static int pk_get_ecparams( unsigned char **p, const unsigned char *end,
return( 0 );
}
/*
* Import a point from unsigned binary data (SEC1 2.3.4), sloppy version:
* accepts compressed point, but then don't fill the Y coordinate, only its
* parity bit. This is a hack to be able to read SpecifiedECDomain to the
* degree that we can check if it is one of the known groups,
* see pk_group_from_specified() and ultimately pk_group_id_from_specified().
*/
static int pk_ecp_point_read_sloppy( const ecp_group *grp, ecp_point *pt,
const unsigned char *buf, size_t ilen )
{
int ret;
size_t plen;
if( ilen == 1 && buf[0] == 0x00 )
return( ecp_set_zero( pt ) );
plen = mpi_size( &grp->P );
if( ilen == 2 * plen + 1 && buf[0] == 0x04 )
{
MPI_CHK( mpi_read_binary( &pt->X, buf + 1, plen ) );
MPI_CHK( mpi_read_binary( &pt->Y, buf + 1 + plen, plen ) );
MPI_CHK( mpi_lset( &pt->Z, 1 ) );
}
else if( ilen == plen + 1 && ( buf[0] == 0x02 || buf[0] == 0x03 ) )
{
MPI_CHK( mpi_read_binary( &pt->X, buf + 1, plen ) );
MPI_CHK( mpi_lset( &pt->Y, buf[0] - 2 ) );
MPI_CHK( mpi_lset( &pt->Z, 1 ) );
}
else
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
cleanup:
return( ret );
}
/*
* Parse a SpecifiedECDomain (SEC 1 C.2) and (mostly) fill the group with it.
* WARNING: the resulting group should only be used with
@ -344,11 +307,27 @@ static int pk_group_from_specified( const asn1_buf *params, ecp_group *grp )
/*
* ECPoint ::= OCTET STRING
*/
if( ( ret = asn1_get_tag( &p, end, &len, ASN1_OCTET_STRING ) ) != 0 ||
( ret = pk_ecp_point_read_sloppy( grp, &grp->G,
( const unsigned char *) p, len ) ) != 0 )
if( ( ret = asn1_get_tag( &p, end, &len, ASN1_OCTET_STRING ) ) != 0 )
return( POLARSSL_ERR_PK_KEY_INVALID_FORMAT + ret );
if( ( ret = ecp_point_read_binary( grp, &grp->G,
( const unsigned char *) p, len ) ) != 0 )
{
/*
* If we can't read the point because it's compressed, cheat by
* reading only the X coordinate and the parity bit of Y.
*/
if( ret != POLARSSL_ERR_ECP_FEATURE_UNAVAILABLE ||
( p[0] != 0x02 && p[0] != 0x03 ) ||
len != mpi_size( &grp->P ) + 1 ||
mpi_read_binary( &grp->G.X, p + 1, len - 1 ) != 0 ||
mpi_lset( &grp->G.Y, p[0] - 2 ) != 0 ||
mpi_lset( &grp->G.Z, 1 ) != 0 )
{
return( POLARSSL_ERR_PK_KEY_INVALID_FORMAT );
}
}
p += len;
/*
@ -471,6 +450,10 @@ static int pk_use_ecparams( const asn1_buf *params, ecp_group *grp )
/*
* EC public key is an EC point
*
* The caller is responsible for clearing the structure upon failure if
* desired. Take care to pass along the possible ECP_FEATURE_UNAVAILABLE
* return code of ecp_point_read_binary() and leave p in a usable state.
*/
static int pk_get_ecpubkey( unsigned char **p, const unsigned char *end,
ecp_keypair *key )
@ -478,19 +461,17 @@ static int pk_get_ecpubkey( unsigned char **p, const unsigned char *end,
int ret;
if( ( ret = ecp_point_read_binary( &key->grp, &key->Q,
(const unsigned char *) *p, end - *p ) ) != 0 ||
( ret = ecp_check_pubkey( &key->grp, &key->Q ) ) != 0 )
(const unsigned char *) *p, end - *p ) ) == 0 )
{
ecp_keypair_free( key );
return( POLARSSL_ERR_PK_INVALID_PUBKEY );
ret = ecp_check_pubkey( &key->grp, &key->Q );
}
/*
* We know ecp_point_read_binary consumed all bytes
* We know ecp_point_read_binary consumed all bytes or failed
*/
*p = (unsigned char *) end;
return( 0 );
return( ret );
}
#endif /* POLARSSL_ECP_C */
@ -801,6 +782,15 @@ static int pk_parse_key_sec1_der( ecp_keypair *eck,
if( ( ret = pk_get_ecpubkey( &p, end2, eck ) ) == 0 )
pubkey_done = 1;
else
{
/*
* The only acceptable failure mode of pk_get_ecpubkey() above
* is if the point format is not recognized.
*/
if( ret != POLARSSL_ERR_ECP_FEATURE_UNAVAILABLE )
return( POLARSSL_ERR_PK_KEY_INVALID_FORMAT );
}
}
else if ( ret != POLARSSL_ERR_ASN1_UNEXPECTED_TAG )
{