em5

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  1. Hack time in seconds? I don't think its that much easy. 256 byte key (256! comibations) gives 1684 bit entrophy, which is huge for a brute force attack. Although I am not an expert on encryption, I think the only attack on substitution cipher is frequency analysis, that too probably done on (uncompressed) english text. If text input is compressed (lightning fast compression exists: LZ4 or LZ4_HC) before substitution, even the odd frequency analysis can't be done.
  2. With substitution cipher (a 256 bytes key, which maps what byte swaps to what other byte), it is just a simple assignment like *ciphertext++ = key[*plaintext++];inside the loop. I don't know how much hardware support is going to help in this regard. Is AES (with hardware support) faster than this?
  3. On this forum, someone(RomanZ?) recomemded not to use encrypted secret keys (stars with "D" instead of "A") as they require more work (checksum) and hence more load on ARMs. I just got an idea that if substitution cipher is used instead of AES, is there any way of not having to do more checksums (assuming sum of all bytes is the checksum, it wont change even after encryption). And the encryption would be fast as well and it is compressible as well. And if another encryption is done after compression, it is more hard to break I guess. I am not an expret, just some thoughts. Any possibility?