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204 lines
4.2 KiB

package keys
import (
"encoding/binary"
"errors"
"hash/crc32"
"hash/crc64"
"github.com/howeyc/crc16"
)
// ECC is used for anything that calculates an error-correcting code
type ECC interface {
// AddECC calculates an error-correcting code for the input
// returns an output with the code appended
AddECC([]byte) []byte
// CheckECC verifies if the ECC is proper on the input and returns
// the data with the code removed, or an error
CheckECC([]byte) ([]byte, error)
}
// NoECC is a no-op placeholder, kind of useless... except for tests
type NoECC struct{}
var _ ECC = NoECC{}
func (_ NoECC) AddECC(input []byte) []byte { return input }
func (_ NoECC) CheckECC(input []byte) ([]byte, error) { return input, nil }
// CRC16 does the ieee crc16 polynomial check
type CRC16 struct {
Poly uint16
table *crc16.Table
}
var _ ECC = &CRC16{}
const crc16Size = 2
func NewIBMCRC16() *CRC16 {
return &CRC16{Poly: crc16.IBM}
}
func NewSCSICRC16() *CRC16 {
return &CRC16{Poly: crc16.SCSI}
}
func NewCCITTCRC16() *CRC16 {
return &CRC16{Poly: crc16.CCITT}
}
func (c *CRC16) AddECC(input []byte) []byte {
table := c.getTable()
// get crc and convert to some bytes...
crc := crc16.Checksum(input, table)
check := make([]byte, crc16Size)
binary.BigEndian.PutUint16(check, crc)
// append it to the input
output := append(input, check...)
return output
}
func (c *CRC16) CheckECC(input []byte) ([]byte, error) {
table := c.getTable()
if len(input) <= crc16Size {
return nil, errors.New("input too short, no checksum present")
}
cut := len(input) - crc16Size
data, check := input[:cut], input[cut:]
crc := binary.BigEndian.Uint16(check)
calc := crc16.Checksum(data, table)
if crc != calc {
return nil, errors.New("Checksum does not match")
}
return data, nil
}
func (c *CRC16) getTable() *crc16.Table {
if c.table == nil {
if c.Poly == 0 {
c.Poly = crc16.IBM
}
c.table = crc16.MakeTable(c.Poly)
}
return c.table
}
// CRC32 does the ieee crc32 polynomial check
type CRC32 struct {
Poly uint32
table *crc32.Table
}
var _ ECC = &CRC32{}
func NewIEEECRC32() *CRC32 {
return &CRC32{Poly: crc32.IEEE}
}
func NewCastagnoliCRC32() *CRC32 {
return &CRC32{Poly: crc32.Castagnoli}
}
func NewKoopmanCRC32() *CRC32 {
return &CRC32{Poly: crc32.Koopman}
}
func (c *CRC32) AddECC(input []byte) []byte {
table := c.getTable()
// get crc and convert to some bytes...
crc := crc32.Checksum(input, table)
check := make([]byte, crc32.Size)
binary.BigEndian.PutUint32(check, crc)
// append it to the input
output := append(input, check...)
return output
}
func (c *CRC32) CheckECC(input []byte) ([]byte, error) {
table := c.getTable()
if len(input) <= crc32.Size {
return nil, errors.New("input too short, no checksum present")
}
cut := len(input) - crc32.Size
data, check := input[:cut], input[cut:]
crc := binary.BigEndian.Uint32(check)
calc := crc32.Checksum(data, table)
if crc != calc {
return nil, errors.New("Checksum does not match")
}
return data, nil
}
func (c *CRC32) getTable() *crc32.Table {
if c.table == nil {
if c.Poly == 0 {
c.Poly = crc32.IEEE
}
c.table = crc32.MakeTable(c.Poly)
}
return c.table
}
// CRC64 does the ieee crc64 polynomial check
type CRC64 struct {
Poly uint64
table *crc64.Table
}
var _ ECC = &CRC64{}
func NewISOCRC64() *CRC64 {
return &CRC64{Poly: crc64.ISO}
}
func NewECMACRC64() *CRC64 {
return &CRC64{Poly: crc64.ECMA}
}
func (c *CRC64) AddECC(input []byte) []byte {
table := c.getTable()
// get crc and convert to some bytes...
crc := crc64.Checksum(input, table)
check := make([]byte, crc64.Size)
binary.BigEndian.PutUint64(check, crc)
// append it to the input
output := append(input, check...)
return output
}
func (c *CRC64) CheckECC(input []byte) ([]byte, error) {
table := c.getTable()
if len(input) <= crc64.Size {
return nil, errors.New("input too short, no checksum present")
}
cut := len(input) - crc64.Size
data, check := input[:cut], input[cut:]
crc := binary.BigEndian.Uint64(check)
calc := crc64.Checksum(data, table)
if crc != calc {
return nil, errors.New("Checksum does not match")
}
return data, nil
}
func (c *CRC64) getTable() *crc64.Table {
if c.table == nil {
if c.Poly == 0 {
c.Poly = crc64.ISO
}
c.table = crc64.MakeTable(c.Poly)
}
return c.table
}