add text on deterministic CBOR encoding

draft/digital-credentials-harmonized-presentation.md

@@ -88,6 +88,17 @@ To be completed.
 # Symbols and abbreviated terms
 
 To be completed.
+
+# CBOR Encoding {#cbor-encoding}
+
+All CBOR data items defined in this document shall be encoded in accordance with the core deterministic encoding requirements defined in [RFC 8949, Section 4.2.1](https://www.rfc-editor.org/rfc/rfc8949#section-4.2.1).
+
+The floating-point values NaN, Infinity and -Infinity shall not be used.
+
+These requirements do not apply to the content of byte strings that carry structures defined outside this document (e.g. mdoc data structures like `Document` or `DeviceEngagement`). Those external data structures are conveyed and processed as received.
+
+> **Note:** The deterministic serialization defined in draft-ietf-cbor-serialization [2] is the same as RFC 8949, Section 4.2.1 except for the encoding of NaN values, which are not used in this document.
+
 # Credential Request
 > This section does not yet have working group consensus, which is tracked in [issue #24](https://github.com/openid/dchp/issues/24).
 
@@ -246,6 +257,8 @@ The transaction transcript provides a cryptographic context binding across all p
 
 Because deterministic CBOR encoding (RFC 8949 §4.2) is required throughout this protocol, the transcript is defined as a **CBOR map** rather than a fixed-order array. Deterministic CBOR guarantees a unique canonical byte encoding for any given map value, making it safe to hash or sign over without ambiguity. This is the key difference from the ISO/IEC 18013-5 `SessionTranscript` array, which used a fixed order precisely to achieve the same determinism property.
 
+The transcripts are never transmitted and the verifier and the wallet each construct them independently and shall encode them as specified in [CBOR Encoding](#cbor-encoding), so that both obtain identical byte representations.
+
 Two transcript types are defined:
 
 - **`ReaderTransactionTranscript`** — constructed by the **verifier** and used in reader authentication and response encryption.
@@ -518,7 +531,8 @@ SdJwtData = tstr   ; SD-JWT combined presentation string
 ```cddl
 ; ==========================================
 ; TRANSACTION TRANSCRIPTS
-; Deterministic CBOR encoding (RFC 8949 §4.2) is REQUIRED for all transcript values.
+; Transcripts shall be encoded as specified in the "CBOR Encoding" clause
+; (RFC 8949, Section 4.2.1).
 ; ==========================================
 
 ; Used by the verifier: for reader authentication and as info parameter for response encryption.
@@ -590,15 +604,19 @@ Clause 7 (see <https://www.iso.org/directives-and-policies.html>).
 [1] ISO/IEC Directives, Part 2, *Principles and rules for the structure and
 drafting of ISO and IEC documents*
 
+[2] IETF Internet-Draft draft-ietf-cbor-serialization, *CBOR Serialization and
+Determinism* (work in progress)
+
 # Acknowledgements {#Acknowledgements}
 
 We would like to thank TBD for their
 valuable feedback and contributions to this specification.
 
 # Document History
 
-   [[ To be removed from the final specification ]]
+[[ To be removed from the final specification ]]
 
-   -00
+-00
 
-   * initial working draft
+ * adds definition on deterministic cbor encoding
+ * initial working draft