Golang AES StreamReader加密 – 示例省略了对加密数据的任何身

我正在实现一个基于official Golang cipher example的文件加密后台守护进程：

func ExampleStreamReader() {
    key := []byte("example key 1234")

    inFile,err := os.Open("encrypted-file")
    if err != nil {
        panic(err)
    }
    defer inFile.Close()

    block,err := aes.NewCipher(key)
    if err != nil {
        panic(err)
    }

    // If the key is unique for each ciphertext,then it's ok to use a zero
    // IV.
    var iv [aes.BlockSize]byte
    stream := cipher.NewOFB(block,iv[:])

    outFile,err := os.OpenFile("decrypted-file",os.O_WRONLY|os.O_CREATE|os.O_TRUNC,0600)
    if err != nil {
        panic(err)
    }
    defer outFile.Close()

    reader := &cipher.StreamReader{S: stream,R: inFile}
    // Copy the input file to the output file,decrypting as we go.
    if _,err := io.Copy(outFile,reader); err != nil {
        panic(err)
    }

    // Note that this example is simplistic in that it omits any
    // authentication of the encrypted data. If you were actually to use
    // StreamReader in this manner,an attacker could flip arbitrary bits in
    // the output.
}

func ExampleStreamWriter() {
    key := []byte("example key 1234")

    inFile,err := os.Open("plaintext-file")
    if err != nil {
        panic(err)
    }
    defer inFile.Close()

    block,err := os.OpenFile("encrypted-file",0600)
    if err != nil {
        panic(err)
    }
    defer outFile.Close()

    writer := &cipher.StreamWriter{S: stream,W: outFile}
    // Copy the input file to the output file,encrypting as we go.
    if _,err := io.Copy(writer,inFile); err != nil {
        panic(err)
    }

    // Note that this example is simplistic in that it omits any
    // authentication of the encrypted data. If you were actually to use
    // StreamReader in this manner,an attacker could flip arbitrary bits in
    // the decrypted result.
}

以下引用是什么意思？关于我应该注意什么才能提供安全的加密和解密？

Note that this example is simplistic in that it
omits any authentication of the encrypted data. If you were actually
to use StreamReader in this manner,an attacker could flip arbitrary
bits in the output.

谢谢！