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unlock-music-cli/algo/qmc/key_dec.go

112 lines
2.2 KiB
Go

package qmc
import (
"encoding/base64"
"errors"
"math"
"golang.org/x/crypto/tea"
)
func simpleMakeKey(salt byte, length int) []byte {
keyBuf := make([]byte, length)
for i := 0; i < length; i++ {
tmp := math.Tan(float64(salt) + float64(i)*0.1)
keyBuf[i] = byte(math.Abs(tmp) * 100.0)
}
return keyBuf
}
func DecryptKey(rawKey []byte) ([]byte, error) {
rawKeyDec := make([]byte, base64.StdEncoding.DecodedLen(len(rawKey)))
_, err := base64.StdEncoding.Decode(rawKeyDec, rawKey)
if err != nil {
return nil, err
}
simpleKey := simpleMakeKey(106, 8)
teaKey := make([]byte, 16)
for i := 0; i < 8; i++ {
teaKey[i<<1] = simpleKey[i]
teaKey[i<<1+1] = rawKeyDec[i]
}
rs, err := decryptTencentTea(rawKeyDec[8:], teaKey)
if err != nil {
return nil, err
}
return append(rawKeyDec[:8], rs...), nil
}
func decryptTencentTea(inBuf []byte, key []byte) ([]byte, error) {
const saltLen = 2
const zeroLen = 7
if len(inBuf)%8 != 0 {
return nil, errors.New("inBuf size not a multiple of the block size")
}
if len(inBuf) < 16 {
return nil, errors.New("inBuf size too small")
}
blk, err := tea.NewCipherWithRounds(key, 32)
if err != nil {
return nil, err
}
destBuf := make([]byte, 8)
blk.Decrypt(destBuf, inBuf)
padLen := int(destBuf[0] & 0x7)
outLen := len(inBuf) - 1 - padLen - saltLen - zeroLen
if padLen+saltLen != 8 {
return nil, errors.New("invalid pad len")
}
out := make([]byte, outLen)
ivPrev := make([]byte, 8)
ivCur := inBuf[:8]
inBufPos := 8
destIdx := 1 + padLen
cryptBlock := func() {
ivPrev = ivCur
ivCur = inBuf[inBufPos : inBufPos+8]
xor8Bytes(destBuf, destBuf, inBuf[inBufPos:inBufPos+8])
blk.Decrypt(destBuf, destBuf)
inBufPos += 8
destIdx = 0
}
for i := 1; i <= saltLen; {
if destIdx < 8 {
destIdx++
i++
} else if destIdx == 8 {
cryptBlock()
}
}
outPos := 0
for outPos < outLen {
if destIdx < 8 {
out[outPos] = destBuf[destIdx] ^ ivPrev[destIdx]
destIdx++
outPos++
} else if destIdx == 8 {
cryptBlock()
}
}
for i := 1; i <= zeroLen; i++ {
if destBuf[destIdx] != ivPrev[destIdx] {
return nil, errors.New("zero check failed")
}
}
return out, nil
}
func xor8Bytes(dst, a, b []byte) {
for i := 0; i < 8; i++ {
dst[i] = a[i] ^ b[i]
}
}