Re: [quicwg/base-drafts] Define an anti-forgery limit (#3620)

[ianswett <[e-mail]>]

@ianswett approved this pull request.



> +The usage limits defined in TLS 1.3 exist to provide protection against attacks
+on confidentiality and apply to successful applications of AEAD protection. The
+integrity protections in authenticated encryption also depend on limiting the
+number of attempts to forge packets. TLS achieves this by closing connections
+after any record fails an authentication check. In comparison, QUIC ignores any
+packet that cannot be authenticated, allowing multiple attempts at defeating
+integrity protection.
+
+Endpoints MUST count the number of packets that are received but cannot be
+authenticated. Packet protection keys MUST NOT be used for removing packet
+protection after authentication fails on more than a per-AEAD limit. Endpoints
+MUST initiate a key update before reaching this limit. Applying a limit reduces
+the probability than attacker is able to successfully forge a packet; see
+{{AEBounds}} and {{ROBUST}}.
+
+For AEAD_AES_128_GCM and AEAD_AES_256_GCM, and AEAD_CHACHA20_POLY1305 the

```suggestion
For AEAD_AES_128_GCM, AEAD_AES_256_GCM, and AEAD_CHACHA20_POLY1305 the
```

> +number of packets that fail authentication MUST NOT exceed 2^36. Note that the
+analysis in {{AEBounds}} supports a higher limit for the AEAD_AES_128_GCM and
+AEAD_AES_256_GCM, but this specification recommends a lower limit. For
+AEAD_AES_128_CCM the number of packets that fail authentication MUST NOT exceed
+2^24.5; see {{ccm-bounds}}.
+
+Any TLS cipher suite that is specified for use with QUIC MUST define limits on
+the use of the associated AEAD function that preserves margins for
+confidentiality and integrity. That is, limits MUST be specified for the number
+of packets that can be authenticated and for the number packets that can fail
+authentication.  Any limits SHOULD reference any analysis upon which values are
+based and describe any assumptions used in that analysis.
+
+Note:
+
+: These limits were originally calculated based using assumptions about the

```suggestion
: These limits were originally calculated using assumptions about the
```

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