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Forbid the sender from sending duplicate supported groups entries. #1354

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Forbid the sender from sending duplicate supported groups entries. #1354

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3 changes: 2 additions & 1 deletion draft-ietf-tls-rfc8446bis.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2245,7 +2245,8 @@ Finite Field Groups (DHE):
{:br }

Items in "named_group_list" are ordered according to the sender's
preferences (most preferred choice first).
preferences (most preferred choice first). The "named_group_list"
MUST NOT contain any duplicate entries.
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When you specify a requirement on the sender, it always helps to specify how the receiver might react if the sender misbehaves. In this case, I think it best to only allow the receiver to reject the handshake, rather than require it. After all, I believe that some implementations are tolerant of that.

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MUST NOT contain any duplicate entries.
MUST NOT contain any duplicate entries. A sender MAY abort a connection
with a fatal illegal_parameter alert if it detects a duplicate entry.

(I'm guessing the alert type here.)

More generally, do we want to do this sort of thing with all such lists, not just groups? key exchange mode? certificate type? etc...

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yes, probably "MAY abort a connection with an illegal_parameter Alert"


As of TLS 1.3, servers are permitted to send the "supported_groups"
extension to the client. Clients MUST NOT act upon any information
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