public int getCiphertextOverheadSizeBytes() {
    if (variant == Variant.NO_PREFIX) {
      return getTagSizeBytes() + getIvSizeBytes();
    }
    if (variant == Variant.TINK || variant == Variant.CRUNCHY) {
      return getTagSizeBytes() + getIvSizeBytes() + PREFIX_SIZE_IN_BYTES;
    }
    throw new IllegalStateException("Unknown variant");
  }
Returns the size of the overhead added to the actual ciphertext (i.e. the size of the IV plus
the size of the security relevant tag plus the size of the prefix with which this key prefixes
the ciphertext.
java_src/src/main/java/com/google/crypto/tink/aead/AesCtrHmacAeadParameters.java