package kcp import ( "crypto/cipher" "encoding/binary" "hash/fnv" "github.com/v2fly/v2ray-core/v5/common" ) // SimpleAuthenticator is a legacy AEAD used for KCP encryption. type SimpleAuthenticator struct{} // NewSimpleAuthenticator creates a new SimpleAuthenticator func NewSimpleAuthenticator() cipher.AEAD { return &SimpleAuthenticator{} } // NonceSize implements cipher.AEAD.NonceSize(). func (*SimpleAuthenticator) NonceSize() int { return 0 } // Overhead implements cipher.AEAD.NonceSize(). func (*SimpleAuthenticator) Overhead() int { return 6 } // Seal implements cipher.AEAD.Seal(). func (a *SimpleAuthenticator) Seal(dst, nonce, plain, extra []byte) []byte { dst = append(dst, 0, 0, 0, 0, 0, 0) // 4 bytes for hash, and then 2 bytes for length binary.BigEndian.PutUint16(dst[4:], uint16(len(plain))) dst = append(dst, plain...) fnvHash := fnv.New32a() common.Must2(fnvHash.Write(dst[4:])) fnvHash.Sum(dst[:0]) dstLen := len(dst) xtra := 4 - dstLen%4 if xtra != 4 { dst = append(dst, make([]byte, xtra)...) } xorfwd(dst) if xtra != 4 { dst = dst[:dstLen] } return dst } // Open implements cipher.AEAD.Open(). func (a *SimpleAuthenticator) Open(dst, nonce, cipherText, extra []byte) ([]byte, error) { dst = append(dst, cipherText...) dstLen := len(dst) xtra := 4 - dstLen%4 if xtra != 4 { dst = append(dst, make([]byte, xtra)...) } xorbkd(dst) if xtra != 4 { dst = dst[:dstLen] } fnvHash := fnv.New32a() common.Must2(fnvHash.Write(dst[4:])) if binary.BigEndian.Uint32(dst[:4]) != fnvHash.Sum32() { return nil, newError("invalid auth") } length := binary.BigEndian.Uint16(dst[4:6]) if len(dst)-6 != int(length) { return nil, newError("invalid auth") } return dst[6:], nil }