+
+/*
+ * ASN.1 DER decoding routines
+ */
+static int asn1_get_len( unsigned char **p,
+ unsigned char *end,
+ int *len )
+{
+ if( ( end - *p ) < 1 )
+ return( POLARSSL_ERR_ASN1_OUT_OF_DATA );
+
+ if( ( **p & 0x80 ) == 0 )
+ *len = *(*p)++;
+ else
+ {
+ switch( **p & 0x7F )
+ {
+ case 1:
+ if( ( end - *p ) < 2 )
+ return( POLARSSL_ERR_ASN1_OUT_OF_DATA );
+
+ *len = (*p)[1];
+ (*p) += 2;
+ break;
+
+ case 2:
+ if( ( end - *p ) < 3 )
+ return( POLARSSL_ERR_ASN1_OUT_OF_DATA );
+
+ *len = ( (*p)[1] << 8 ) | (*p)[2];
+ (*p) += 3;
+ break;
+
+ default:
+ return( POLARSSL_ERR_ASN1_INVALID_LENGTH );
+ break;
+ }
+ }
+
+ if( *len > (int) ( end - *p ) )
+ return( POLARSSL_ERR_ASN1_OUT_OF_DATA );
+
+ return( 0 );
+}
+
+static int asn1_get_tag( unsigned char **p,
+ unsigned char *end,
+ int *len, int tag )
+{
+ if( ( end - *p ) < 1 )
+ return( POLARSSL_ERR_ASN1_OUT_OF_DATA );
+
+ if( **p != tag )
+ return( POLARSSL_ERR_ASN1_UNEXPECTED_TAG );
+
+ (*p)++;
+
+ return( asn1_get_len( p, end, len ) );
+}
+
+static int asn1_get_int( unsigned char **p,
+ unsigned char *end,
+ int *val )
+{
+ int ret, len;
+
+ if( ( ret = asn1_get_tag( p, end, &len, ASN1_INTEGER ) ) != 0 )
+ return( ret );
+
+ if( len > (int) sizeof( int ) || ( **p & 0x80 ) != 0 )
+ return( POLARSSL_ERR_ASN1_INVALID_LENGTH );
+
+ *val = 0;
+
+ while( len-- > 0 )
+ {
+ *val = ( *val << 8 ) | **p;
+ (*p)++;
+ }
+
+ return( 0 );
+}
+
+static int asn1_get_mpi( unsigned char **p,
+ unsigned char *end,
+ mpi *X )
+{
+ int ret, len;
+
+ if( ( ret = asn1_get_tag( p, end, &len, ASN1_INTEGER ) ) != 0 )
+ return( ret );
+
+ ret = mpi_read_binary( X, *p, len );
+
+ *p += len;
+
+ return( ret );
+}
+
+