Question about RFC 6455 Sec-Websocket-Key header

• From: Robert Rothenberg <robrwo@gmail.com>
• Date: Fri, 27 Jun 2025 19:00:06 +0100
• To: ietf-http-wg@w3.org
• Message-ID: <ef8b5d72-df7e-4eeb-a521-509d8d684ffb@gmail.com>

Looking at RFC 6455 on WebSockets, it says

 > The value of this header field MUST be a nonce consisting of a 
randomly selected 16-byte value that has been base64-encoded (see 
Section 4 of [RFC4648]).  The nonce MUST be selected randomly for each 
connection.

I am assuming this should use a CSPRNG to generate the random bytes. But 
as far as I can tell, there is nothing in the RFC that explicitly says 
that about this field.

Does it matter how those bytes are generated, or was this an oversight?

Note that the discussion of the masking key says "The masking key needs 
to be unpredictable; thus, the masking key MUST be derived from a strong 
source of entropy, and the masking key for a given frame MUST NOT make 
it simple for a server/proxy to predict the masking key for a subsequent 
frame."

Regards,
Robert

Received on Friday, 27 June 2025 18:12:13 UTC