fix 543: improve COSE_Key spec language and add COSE_Key examples

index.bs

@@ -2487,7 +2487,7 @@ object=] for a given credential. It has the following format:
     <tr>
         <td><dfn>credentialIdLength</dfn></td>
         <td>2</td>
-        <td>Byte length L of Credential ID</td>
+        <td>Byte length <strong>L</strong> of Credential ID</td>
     </tr>
     <tr>
         <td><dfn>credentialId</dfn></td>
@@ -2498,16 +2498,92 @@ object=] for a given credential. It has the following format:
         <td><dfn>credentialPublicKey</dfn></td>
         <td>variable</td>
         <td>
-            The [=credential public key=] encoded in COSE_Key format, as defined in Section 7 of [[!RFC8152]].
-	        The encoded [=credential public key=] MUST contain the "alg" parameter and MUST NOT contain any other optional
-	        parameters. The "alg" parameter MUST contain a {{COSEAlgorithmIdentifier}} value.
+            The [=credential public key=] encoded in COSE_Key format,
+            as defined in Section 7 of [[RFC8152]], using the [=CTAP canonical CBOR encoding form=].
+            The COSE_Key-encoded [=credential public key=] MUST contain the optional "alg" parameter and MUST NOT
+            contain any other optional parameters. The "alg" parameter MUST contain a {{COSEAlgorithmIdentifier}} value.
+            The encoded [=credential public key=] MUST also contain any additional required parameters stipulated by the
+            relevant key type specification, i.e., required for the key type "kty" and algorithm "alg" (see Section 8 of
+            [[RFC8152]]).
         </td>
     </tr>
 </table>
 
   NOTE: The names in the Name column in the above table are only for reference within this document, and are not present in the
   actual representation of the [=attested credential data=].
 
+#### Examples of `credentialPublicKey` Values encoded in COSE_Key format #### {#sctn-encoded-credPubKey-examples}
+
+This section provides examples of COSE_Key-encoded Eliptic Curve and RSA public keys for the ES256, PS256, and RS256
+signature algorithms. These examples adhere to the rules defined above for the [=credentialPublicKey=] value, and are presented in [[CDDL]] for clarity. 
+
+[[RFC8152]] [Section 7](https://tools.ietf.org/html/rfc8152#section-7) defines the general framework for all
+COSE_Key-encoded keys.
+Specific key types for specific algorithms are defined in other sections of [[RFC8152]] as well as in other specifications,
+as noted below.
+
+Below is an example of a COSE_Key-encoded Eliptic Curve public key in EC2 format (see [[RFC8152]]
+[Section 13.1](https://tools.ietf.org/html/rfc8152#section-13.1)), on the P-256 curve, to be used with the ES256 signature
+algorithm (ECDSA w/ SHA-256, see [[RFC8152]] [Section 8.1](https://tools.ietf.org/html/rfc8152#section-8.1)):
+
+<pre class="example" highlight="json">
+  {
+    1:   2,  ; kty: EC2 key type
+    3:  -7,  ; alg: ES256 signature algorithm
+   -1:   1,  ; crv: P-256 curve
+   -2:   x,  ; x-coordinate as byte string 32 bytes in length
+             ; e.g., in hex: 65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c08551d
+   -3:   y   ; y-coordinate as byte string 32 bytes in length
+             ; e.g., in hex: 1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd0084d19c
+  }
+</pre>
+
+Below is the above Eliptic Curve public key encoded in the [=CTAP canonical CBOR encoding form=], whitespace and line breaks
+are included here for clarity and to match the [[CDDL]] presentation above:
+
+<pre class="example" highlight="json">
+  A5
+     01  02
+
+     03  26
+
+     20  01
+
+     21  58 20   65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c08551d
+
+     22  58 20   1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd0084d19c
+</pre>
+
+
+Below is an example of a COSE_Key-encoded 2048-bit RSA public key (see [[RFC8230]] [Section 4](https://tools.ietf.org/html/rfc8230#section-4)),
+to be used with the PS256 signature algorithm
+(RSASSA-PSS with SHA-256, see [[RFC8230]] [Section 2](https://tools.ietf.org/html/rfc8230#section-2)):
+
+<pre class="example" highlight="json">
+  {
+    1:   3,  ; kty: RSA key type
+    3: -37,  ; alg: PS256
+   -1:   n,  ; n:   RSA modulus n byte string 256 bytes in length
+             ;      e.g., in hex (middle bytes elided for brevity): DB5F651550...6DC6548ACC3
+   -2:   e   ; e:   RSA public exponent e byte string 3 bytes in length
+             ;      e.g., in hex: 010001
+  }
+</pre>
+
+Below is an example of the same COSE_Key-encoded RSA public key as above, 
+to be used with the RS256 signature algorithm (RSASSA-PKCS1-v1_5 with SHA-256, see [[#sctn-cose-alg-reg]]):
+
+<pre class="example" highlight="json">
+  {
+    1:   3,  ; kty: RSA key type
+    3:-257,  ; alg: RS256
+   -1:   n,  ; n:   RSA modulus n byte string 256 bytes in length
+             ;      e.g., in hex (middle bytes elided for brevity): DB5F651550...6DC6548ACC3
+   -2:   e   ; e:   RSA public exponent e byte string 3 bytes in length
+             ;      e.g., in hex: 010001
+  }
+</pre>
+
 
 ### Attestation Statement Formats ### {#attestation-formats}