Defer base-encoding to each Create Proof algorithm.

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@@ -450,14 +450,12 @@ <h4>DataIntegrityProof</h4>
 The `cryptosuite` property of the proof MUST be `ecdsa-rdfc-2019` or `ecdsa-jcs-2019`.
           </p>
           <p>
-The value of the `proofValue` property of the proof MUST be an ECDSA signature
-produced according to [[FIPS-186-5]] using the curves and hashes as specified in
-section [[[#algorithms]]], encoded according to section 7 of [[RFC4754]]
-(sometimes referred to as the IEEE P1363 format), and encoded using the
-base-58-btc header and alphabet as described in the
-<a href="https://www.w3.org/TR/vc-data-integrity/#multibase-0">
-Multibase section</a> of [[VC-DATA-INTEGRITY]]. The ECDSA signature SHOULD use
-the <em>deterministic</em> ECDSA signature variant described in [[FIPS-186-5]].
+The value of the `proofValue` property of the proof MUST be an ECDSA signature,
+expressed according to section 7 of [[RFC4754]] (sometimes referred to as the
+IEEE P1363 format), produced according to [[FIPS-186-5]] using the curves,
+hashes, and base-encoding as specified in section [[[#algorithms]]]. The ECDSA
+signature SHOULD use the <em>deterministic</em> ECDSA signature variant
+described in [[FIPS-186-5]].
           </p>
 
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