Merge pull request #172 from oauth-wg/pb/considerations2

add implementation consideration for Default Values and Double Alloca…

draft-ietf-oauth-status-list.md

@@ -692,10 +692,22 @@ TODO evaluate definition of Status List Provider?
 
 The lifetime of a Status List (and the Status List Token) depends on the lifetime of its Referenced Tokens. Once all Referenced Tokens are expired, the Issuer may stop serving the Status List (and the Status List Token).
 
-Referenced Tokens may be regularly re-issued to increase security or to mitigate linkability and prevent tracking by Relying Parties. In this case, every Referenced Token MUST have a fresh Status List entry.
+Referenced Tokens may be regularly re-issued to mitigate linkability of presentations to Relying Parties. In this case, every re-issued Referenced Token MUST have a fresh Status List entry in order to prevent this becoming possible source of correlation.
 
 Referenced Tokens may also be issued in batches, such that Holders can use individual tokens for every transaction. In this case, every Referenced Token MUST have a dedicated Status List entry. Revoking batch issued Referenced Tokens might reveal this correlation later on.
 
+## Default Values and Double Allocation
+
+Implementations producing Status Lists are RECOMMENDED to initialize the Status List byte array with a default value and provide this as an initialization parameter to the Issuer. The Issuer is RECOMMENDED to use a default value that represents the most common value for its Referenced Tokens to avoid an update during issuance.
+
+Implementations producing Status Lists are RECOMMENDED to prevent double allocation, i.e. re-using the same `uri` and `index` for multiple Referenced Tokens. The Issuer MUST prevent any unintended double allocation by using the Status List.
+
+## Status List Size
+
+The Status List Issuer may increase the size of a Status List if it requires indices for additional Referenced Tokens. It is RECOMMENDED that the size of a Status List in bits is divisible in bytes (8 bits) without a remainder, i.e. `size-in-bits` % 8 = 0.
+
+The Status List Issuer may chunk its Referenced Tokens into multiple Status Lists to reduce the transmission size of an individual Status List Token. This may be useful for setups where some entities operate in constrained environments, e.g. for mobile internet or embedded devices.
+
 # IANA Considerations
 
 ## JSON Web Token Claims Registration
@@ -927,6 +939,7 @@ for their valuable contributions, discussions and feedback to this specification
 
 -04
 
+* add implementation consideration for Default Values, Double Allocation and Status List Size
 * add privacy consideration on using private relay protocols
 * add privacy consideration on observability of outsiders
 * add security considerations on correct parsing and decoding