40 lines
783 B
Go
40 lines
783 B
Go
package qmc
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import "errors"
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type mapCipher struct {
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key []byte
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box []byte
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size int
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}
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func NewMapCipher(key []byte) (*mapCipher, error) {
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if len(key) == 0 {
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return nil, errors.New("qmc/cipher_map: invalid key size")
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}
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c := &mapCipher{key: key, size: len(key)}
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c.box = make([]byte, c.size)
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return c, nil
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}
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func (c *mapCipher) getMask(offset int) byte {
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if offset > 0x7FFF {
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offset %= 0x7FFF
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}
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idx := (offset*offset + 71214) % c.size
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return c.rotate(c.key[idx], byte(idx)&0x7)
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}
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func (c *mapCipher) rotate(value byte, bits byte) byte {
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rotate := (bits + 4) % 8
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left := value << rotate
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right := value >> rotate
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return left | right
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}
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func (c *mapCipher) Decrypt(buf []byte, offset int) {
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for i := 0; i < len(buf); i++ {
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buf[i] ^= c.getMask(offset + i)
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}
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}
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