I recentely faced the issue of random access decryption while AES-GCM was being used. I said this person that the underlying CTR should allow parallelization but I have no idea how authentication comes into play.
Now I know that one of the cool features of CTR is that you can decrypt any block without needing to involve any other blocks. I also know that CTR is part of the basis for GCM.
Now my question(s) are:
- Can one somehow parallelize encryption of data in GCM mode (only CTR part? Parts of the MAC as well?)
- Is it possible to get random access to decrypted ciphertexts (+ fast verification?) or is at least somehow possible to parallelize decryption and authentication (do either of both in parallel or internally parallelize?)?