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Comment by hadcomplained | Hacker News Reader

For downvoters - constructive counterarguments are welcome.

I don’t mean to be rude, but it’s quite obvious by what you wrote that you are barely literate in cryptography, yet you are fairly certain of yourself. Your confidence is misplaced. This isn’t the type of thing that encourages actual experts to bother replying.

Examples: “side channel such as a backdoor that secretly stores keys used somewhere”, “blowfish”, nonsensical mixing of block ciphers and stream ciphers without regard for the complete construction or the implementation (by far the largest weak point), etc.

"by far the largest weak point"

Well, if the nested ciphers are all properly implemented AEAD schemes, use unique keys, and don't rely on public key crypto for key exchange, cascading crypto is fine.

Other than that their discourse was that of a novice, sure.

Combining standard algorithms doesn't constitute rolling your own crypto. Arguably, even increasing the number of rounds in a standard cipher doesn't, either.

A back door is not a side channel.

Rolling one's own crypto has become a catch-all phrase. It's of course very important to remember implementing standard algorithms in non-standard way can be incredibly dangerous too. I've seen unauthenticated AES-CBC way too many times. I've seen fingerprints calculated by hashing pre-master secrets (completely insecure), I've seen crypto libraries that rely on completely insecure structures for their RNGs (worst was probably LCG fed from math.random). I've seen fixed IVs with fixed keys, E2EE without fingerprints (way too often), ones with expired primitives (SHA-1 in PGP). I've seen RSA PKCS #1.5 deployed in brand new products (https://trailofbits.files.wordpress.com/2019/07/image13-1.pn...).

So the correct advice is, "don't deviate from best practices, and hire a cryptographer."

Reply on news.ycombinator.com