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unlock-music-cli/algo/kwm/kwm_cipher.go

32 lines
607 B
Go

package kwm
import (
"encoding/binary"
"strconv"
)
type kwmCipher struct {
mask []byte
}
func newKwmCipher(key []byte) *kwmCipher {
return &kwmCipher{mask: generateMask(key)}
}
func generateMask(key []byte) []byte {
keyInt := binary.LittleEndian.Uint64(key)
keyStr := strconv.FormatUint(keyInt, 10)
keyStrTrim := padOrTruncate(keyStr, 32)
mask := make([]byte, 32)
for i := 0; i < 32; i++ {
mask[i] = keyPreDefined[i] ^ keyStrTrim[i]
}
return mask
}
func (c kwmCipher) Decrypt(buf []byte, offset int) {
for i := range buf {
buf[i] ^= c.mask[(offset+i)&0x1F] // equivalent: [i % 32]
}
}