alt Hacker News> Opening an encrypted connection means one very large multiplication. On a 4.77 MHz 8088 it takes minutes.
I've done it.
It took a lot of loop unrolling and optimizations in order to get the TLS 1.2 handshake to complete before the server timed out the connection, but I've successfully gotten it to work, and with only 384 KB of RAM.
The implementation doesn't verify the server certificate (would certainly take too long), but it successfully performs an HTTPS request to Wikipedia as a proof-of-concept.
One of these days I'll clean up the code and post it here.
Replies
Better off just using http://frogfind.com/
and with only 384 KB of RAM.
A 2048-bit RSA key is 256 bytes. A 256-bit symmetric key is 32 bytes and ECDH keys are roughly the same size. The state size of AES is 16 bytes and its S-box is 256 bytes. Efficient implementations use only a few KB of state. The vast majority of cryptographic algorithms just aren't that big, relatively speaking; although as you mention, they are very computationally intense. Hash states are in the dozens to low hundreds of bytes. For TLS implementation, the record buffers are probably going to use the most RAM; 16K each direction + additional overhead.
I‘ve recently tried implementing the Noise protocol on a 7.8 MHz 68000, while it runs in 10 seconds I don’t think there is a way to make it constant time without using addition and running an order of magnitude more slowly :(
MULU operations are not constant time but depend on popcount. That has an easy work around just also do the MULU of the bitwise inverse, both instructions sum to a constant cycle count.
The brick wall I hit is related to the Macintosh SE ram being shared between CPU and video system. Every few cycles the CPU stalls instruction fetching, which turns the both MULUs together take the same amount of time each time into there is slowdown depending on the popcount of the first instruction.
I don’t know if anyone has any solution for this, there is prefetching of one instruction so all should be well, but it seems like the cpu stalls the in progress instruction if the prefetch is stalled.