>UDP for reporting market data because you can't have any latency and TCP for 
>order placement
That is my understanding as well. A recent summary from a company providing 
technology to the financial sector confirms this.
https://www.pico.net/kb/what-are-the-relative-merits-of-tcp-and-udp-in-high-frequency-trading/

>Since HFT is sort of front-running the market but technically it's not so it’s 
>not illegal
Not anymore. However, in 1837 the French government criminalized the private 
use of telegraphic machines, partly to prevent unfair advantages in stock 
markets. This law followed the 1834 optical telegraph hack, often cited as the 
first cybercrime, which involved an early form of "high‑frequency” trading.
https://www.diva-portal.org/smash/get/diva2:2035158/FULLTEXT01.pdf

Cheer,
John

From: Peter Gutmann <[email protected]>
Date: Wednesday, 18 February 2026 at 09:12
To: [email protected] <[email protected]>
Subject: [TLS] Re: forwarding draft-ietf-tls-mlkem-05 use case

Viktor Dukhovni <[email protected]> writes:

>This does not look to me like a compelling rationale.  A high-frequency
>trading system that does not route trades over a connection that was
>established well before market open, and expects to beat the competition by
>minimising connection establishment latency, is perhaps doing it wrong. For
>already established TLS connections latency does not depend on which key
>agreement group was used in the initial handshake.

The following is some years out of date so things may have changed since then
but HFT uses (used) UDP for reporting market data because you can't have any
latency and TCP for order placement because you need reliability, but even
that's modded TCP with anything that would introduce delays or stalls removed.
The interesting stuff isn't the software but the custom hardware used to
minimise any kind of delay, at the time eyewateringly expensive FPGAs (Virtex
UltraScales) but now presumably ASICs.

>One might also point out that the payload of high-frequency trades is not
>likely to be a long-term secret.

Since HFT is sort of front-running the market but technically it's not so it's
not illegal, the secret may only be valuable for a few hundreds of
milliseconds and even if you discover it you can't react fast enough to act on
it yourself.  As you mention above, the logical thing to do would be to set up
the TLS connection before market open and not hope that your TLS handshake
completes in time to get your urgent buy order through.

Peter.
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