package qmc import ( "bytes" "encoding/base64" "errors" "fmt" "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 } const rawKeyPrefixV2 = "QQMusic EncV2,Key:" func DecryptKey(rawKey []byte) ([]byte, error) { rawKeyDec := make([]byte, base64.StdEncoding.DecodedLen(len(rawKey))) n, err := base64.StdEncoding.Decode(rawKeyDec, rawKey) if err != nil { return nil, err } rawKeyDec = rawKeyDec[:n] if bytes.HasPrefix(rawKeyDec, []byte(rawKeyPrefixV2)) { rawKeyDec, err = deriveKeyV2(bytes.TrimPrefix(rawKeyDec, []byte(rawKeyPrefixV2))) if err != nil { return nil, fmt.Errorf("deriveKeyV2 failed: %w", err) } } return deriveKeyV1(rawKeyDec) } func deriveKeyV1(rawKeyDec []byte) ([]byte, error) { if len(rawKeyDec) < 16 { return nil, errors.New("key length is too short") } 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 } var ( deriveV2Key1 = []byte{ 0x33, 0x38, 0x36, 0x5A, 0x4A, 0x59, 0x21, 0x40, 0x23, 0x2A, 0x24, 0x25, 0x5E, 0x26, 0x29, 0x28, } deriveV2Key2 = []byte{ 0x2A, 0x2A, 0x23, 0x21, 0x28, 0x23, 0x24, 0x25, 0x26, 0x5E, 0x61, 0x31, 0x63, 0x5A, 0x2C, 0x54, } ) func deriveKeyV2(raw []byte) ([]byte, error) { buf, err := decryptTencentTea(raw, deriveV2Key1) if err != nil { return nil, err } buf, err = decryptTencentTea(buf, deriveV2Key2) if err != nil { return nil, err } n, err := base64.StdEncoding.Decode(buf, buf) if err != nil { return nil, err } return buf[:n], 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 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] } }