code: func EncryptSymmetric(plaintext []byte, secret []byte) (ciphertext []byte) {
  	if len(secret) != secretLen {
  		PanicSanity(Fmt("Secret must be 32 bytes long, got len %v", len(secret)))
  	}
  	nonce := CRandBytes(nonceLen)
  	nonceArr := [nonceLen]byte{}
  	copy(nonceArr[:], nonce)
  	secretArr := [secretLen]byte{}
  	copy(secretArr[:], secret)
  	ciphertext = make([]byte, nonceLen+secretbox.Overhead+len(plaintext))
  	copy(ciphertext, nonce)
  	secretbox.Seal(ciphertext[nonceLen:nonceLen], plaintext, &nonceArr, &secretArr)
  	return ciphertext
  }
docs: // secret must be 32 bytes long. Use something like Sha256(Bcrypt(passphrase))
  // The ciphertext is (secretbox.Overhead + 24) bytes longer than the plaintext.
  // NOTE: call crypto.MixEntropy() first.