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Implement TLS 1.3 random record padding #5398

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candrews opened this issue May 14, 2020 · 4 comments
Closed

Implement TLS 1.3 random record padding #5398

candrews opened this issue May 14, 2020 · 4 comments

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@candrews
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candrews commented May 14, 2020

The TLS specification (RFC 8446) section 5.4 defines optional Record Padding.

As a security improvement, I suggest that curl implement random record padding.

Record padding is primarily applicable to server as a way to mitigate vulnerabilities such as CRIME and BREACH that involve compression and reflection. But, who knows - there may be some future vulnerability that random record padding will address on the client - it couldn't hurt :)

In OpenSSL, this is done using SSL_CTX_set_record_padding_callback

@jay jay added the TLS label May 14, 2020
@jay
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jay commented May 14, 2020

it couldn't hurt :)

I'm not really feeling this one. I'm concerned about the already tenuous situation with middleboxes.

@candrews
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candrews commented May 14, 2020

Wouldn't middle boxes already be a problem for TLS 1.3 then?

Perhaps a flag/configuration option to optionally enable this would be nice, then down the line if all goes well, it could be enabled by default?

@jay
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jay commented May 14, 2020

Wouldn't middle boxes already be a problem for TLS 1.3 then?

There is middlebox compatibility in OpenSSL (and I assume others).

Perhaps a flag/configuration option to optionally enable this would be nice, then down the line if all goes well, it could be enabled by default?

I don't see a reason to do it by default. We may end up lessening security and compatibility for no good reason. It might allow for a vulnerability instead of preventing one. I really don't know what will happen. As an option I expect it would very obscure, this is the first I'm hearing of it. You could use CURLOPT_SSL_CTX_FUNCTION if you want it.

@bagder
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bagder commented May 18, 2020

Padding is in general a thing people invent when designing protocols and then nobody actually uses when running them since they're a waste of bandwidth. I suspect that's why we've never seen a demand for padding for TLS before.

@bagder bagder closed this as completed in 5646e56 May 18, 2020
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