README
¶
crc32
An implementation of an algorithm to modify a file so that its CRC-32 checksum matches a given value. This requires four sacrificial bytes in the file that will be modified to generate the desired value. A small example:
f, err := os.OpenFile("somefile", O_RDWR, 0) // Remember to open read/write!
if err != nil {
log.Fatal(err)
}
defer f.Close()
if err := crc32.ForceCRC32(f, 0, 0xdeadbeef); err != nil {
log.Fatal(err)
}
In this example the first four bytes in somefile will be modified so that
the CRC-32 checksum of somefile will be 0xdeadbeef however the bytes can
be anywhere in the file, but must be contiguous.
Documentation
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Overview ¶
Package crc32 is an implementation of an algorithm to modify a file so that its CRC-32 checksum matches a given value. This requires four sacrificial bytes in the file that will be modified to generate the desired value.
Index ¶
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func ForceCRC32 ¶
func ForceCRC32(rws io.ReadWriteSeeker, offset int64, desiredCRC uint32) error
ForceCRC32 takes an io.ReadWriteSeeker and updates the four bytes starting at offset such that the IEEE CRC-32 value of the whole stream matches desiredCRC. If the CRC-32 value already matches, no changes are made.
Example ¶
package main
import (
"encoding/hex"
"fmt"
"io"
"os"
"github.com/bodgit/crc32"
)
func main() {
f, err := os.CreateTemp("", "")
if err != nil {
panic(err)
}
defer func() {
if err := f.Close(); err != nil {
panic(err)
}
if err := os.RemoveAll(f.Name()); err != nil {
panic(err)
}
}()
b := []byte("This is a test 0000")
if _, err := f.Write(b); err != nil {
panic(err)
}
if err := crc32.ForceCRC32(f, int64(len(b)-4), 0xdeadbeef); err != nil {
panic(err)
}
if _, err := f.Seek(0, io.SeekStart); err != nil {
panic(err)
}
if _, err := io.ReadFull(f, b); err != nil {
panic(err)
}
fmt.Print(hex.Dump(b))
}
Output: 00000000 54 68 69 73 20 69 73 20 61 20 74 65 73 74 20 99 |This is a test .| 00000010 3c 5f 27 |<_'|
Types ¶
This section is empty.
Source Files