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// Copyright (c) 2013-2014 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package base58
import (
"crypto/sha256"
"errors"
)
// ErrChecksum indicates that the checksum of a check-encoded string does not verify against
// the checksum.
var ErrChecksum = errors.New("checksum error")
// ErrInvalidFormat indicates that the check-encoded string has an invalid format.
var ErrInvalidFormat = errors.New("invalid format: version and/or checksum bytes missing")
// checksum: first four bytes of sha256^2
func checksum(input []byte) (cksum [4]byte) {
h := sha256.Sum256(input)
h2 := sha256.Sum256(h[:])
copy(cksum[:], h2[:4])
return
}
// CheckEncode prepends a version byte and appends a four byte checksum.
func CheckEncode(input []byte, version byte) string {
b := make([]byte, 0, 1+len(input)+4)
b = append(b, version)
b = append(b, input...)
cksum := checksum(b)
b = append(b, cksum[:]...)
return Encode(b)
}
// CheckDecode decodes a string that was encoded with CheckEncode and verifies the checksum.
func CheckDecode(input string) (result []byte, version byte, err error) {
decoded := Decode(input)
if len(decoded) < 5 {
return nil, 0, ErrInvalidFormat
}
version = decoded[0]
var cksum [4]byte
copy(cksum[:], decoded[len(decoded)-4:])
if checksum(decoded[:len(decoded)-4]) != cksum {
return nil, 0, ErrChecksum
}
payload := decoded[1 : len(decoded)-4]
result = append(result, payload...)
return
}
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