1 // Copyright (c) 2013-2014 The btcsuite developers
2 // Use of this source code is governed by an ISC
3 // license that can be found in the LICENSE file.
4 5 package base58
6 7 import (
8 "errors"
9 10 "crypto/sha256"
11 )
12 13 // ErrChecksum indicates that the checksum of a check-encoded string does not verify against
14 // the checksum.
15 var ErrChecksum = errors.New("checksum error")
16 17 // ErrInvalidFormat indicates that the check-encoded string has an invalid format.
18 var ErrInvalidFormat = errors.New("invalid format: version and/or checksum bytes missing")
19 20 // checksum: first four bytes of sha256^2
21 func checksum(input []byte) (cksum [4]byte) {
22 h := sha256.Sum256(input)
23 h2 := sha256.Sum256(h[:])
24 copy(cksum[:], h2[:4])
25 return
26 }
27 28 // CheckEncode prepends a version byte and appends a four byte checksum.
29 func CheckEncode(input []byte, version byte) string {
30 b := []byte{:0:1+len(input)+4}
31 b = append(b, version)
32 b = append(b, input...)
33 cksum := checksum(b)
34 b = append(b, cksum[:]...)
35 return Encode(b)
36 }
37 38 // CheckDecode decodes a string that was encoded with CheckEncode and verifies the checksum.
39 func CheckDecode(input string) (result []byte, version byte, err error) {
40 decoded := Decode(input)
41 if len(decoded) < 5 {
42 return nil, 0, ErrInvalidFormat
43 }
44 version = decoded[0]
45 var cksum [4]byte
46 copy(cksum[:], decoded[len(decoded)-4:])
47 if checksum(decoded[:len(decoded)-4]) != cksum {
48 return nil, 0, ErrChecksum
49 }
50 payload := decoded[1 : len(decoded)-4]
51 result = append(result, payload...)
52 return
53 }
54