A pet nit, and the standards probably don't permit this, but for encoding 128-bit numbers, I prefer base-57 in my own implementations. 22 characters for a 128-bit encoding, same as base-64. You can split it into two 11-character 64-bit encodings. You can avoid the two non-alphanumeric characters in base-64 as well as the similar-looking characters like l1 and oO0. And it takes less visible space, so a bit easier for debugging and tabular output with otherwise no loss of generality.