Extend the token type registry for batched issuance

draft-ietf-privacypass-architecture.md

@@ -504,6 +504,10 @@ of public metadata.
 arbitrary private information, i.e., information that the Client does not observe
 during Token issuance or redemption. See {{metadata-privacy}} for privacy
 considerations of private metadata.
+1. Batched issuance. This means that Clients can request multiple Tokens in a single
+batch, rather than requesting many Tokens with multiple token requests. Not all
+cryptographic protocols underlying the issuance protocol support batched issuance.
+See {{batch-privacy}} for privacy considerations of batched issuance protocols.
 
 The issuance protocol itself can be any interactive protocol between Client,
 Issuer, or other parties that produces a valid token bound to the Client's
@@ -1101,7 +1105,7 @@ in applying these consistency checks across clients. Failure to apply a
 consistency check can allow Client-specific keys to violate Origin-Client
 unlinkability.
 
-## Partitioning by Side-Channels
+## Partitioning by Side-Channels {#side-channels}
 
 Side-channel attacks, such as those based on timing correlation, could be
 used to reduce anonymity set size. In particular,
@@ -1114,6 +1118,15 @@ be small. Applications should take such side channels into consideration before
 choosing a particular deployment model and type of token challenge and
 redemption context.
 
+## Partitioning by Batched Issuance {#batch-privacy}
+
+Clients that choose to use a batched version of an issuance protocol allow
+the Issuer to link each of the individual token requests in a batch to the
+same Client. If Clients choose different batch sizes, this may reveal
+information to the Issuer that was not otherwise available (except via timing
+side channels; see {{side-channels}}). Consistency in batch sizes is therefore
+an important mitigation against partitioning attacks; see {{rotation-and-consistency}}.
+
 # Security Considerations {#security}
 
 This document describes security and privacy requirements for the Privacy Pass

draft-ietf-privacypass-auth-scheme.md

@@ -371,7 +371,7 @@ Clients ought to store cached tokens based on all of these fields, to
 avoid trying to redeem a token that does not match. Note that each token
 has a unique client nonce, which is sent in token redemption ({{redemption}}).
 
-If a client fetches a batch of multiple tokens for future use that are bound
+If a client fetches multiple tokens for future use that are bound
 to a specific redemption context (the redemption_context in the TokenChallenge
 was not empty), clients SHOULD discard these tokens upon flushing state such as
 HTTP cookies {{?COOKIES=I-D.ietf-httpbis-rfc6265bis}}, or if there is a network
@@ -579,7 +579,7 @@ origins SHOULD include random token types, from the Reserved list of "greased"
 types (defined in {{token-types}}), with some non-trivial probability.
 
 Additionally, for deployments where tokens are not required (such as when tokens
-are used as a way to avoiding showing CAPTCHAs), origins SHOULD randomly

+are used as a way to avoiding showing CAPTCHAs), origins SHOULD randomly
 choose to not challenge clients for tokens with some non-trivial probability.
 This helps origins ensure that their behavior for handling clients that cannot
 redeem tokens is maintained and exercised consistently.
@@ -729,6 +729,11 @@ Private Metadata:
   private metadata; see {{Section 3.5 of ARCHITECTURE}}
   for more details about this property.
 
+Batched Issuance:
+: A Y/N value indicating if the token type supports batched
+  issuance. see {{Section 3.5 of ARCHITECTURE}} for more
+  details about this property.
+
 Nk:
 : The length in bytes of an output authenticator
 
@@ -795,6 +800,9 @@ Public Metadata:
 Private Metadata:
 : N/A
 
+Batched Issuance:
+: N/A
+
 Nk:
 : N/A
 

draft-ietf-privacypass-protocol.md

@@ -138,7 +138,8 @@ Issuers MUST provide two parameters for configuration:
 
 1. Issuer Request URL: A token request URL for generating access tokens.
    For example, an Issuer URL might be
-   https://issuer.example.net/request.
+   https://issuer.example.net/request. Unless otherwise specified and configured, this
+   resource only accepts content with the media type "application/private-token-request".
 2. Issuer Public Key values: A list of Issuer Public Keys for the issuance
    protocol.
 
@@ -793,6 +794,7 @@ following entries.
 * Public Verifiability: N
 * Public Metadata: N
 * Private Metadata: N
+* Batched Issuance: Y
 * Nk: 48
 * Nid: 32
 * Reference: {{private-flow}}
@@ -808,6 +810,7 @@ following entries.
 * Public Verifiability: Y
 * Public Metadata: N
 * Private Metadata: N
+* Batched Issuance: N
 * Nk: 256
 * Nid: 32
 * Reference: {{public-flow}}