@Override
protected Builder withCore(KeyVersionCore kvCore)
throws InvalidProtocolBufferException {
super.withCore(kvCore);
HmacKeyVersionCore core =
kvCore.getExtension(HmacKeyVersionCore.extension);
// Extract info from core
this.matterVector(core.getMatter().toByteArray());
switch (core.getAlgorithm()) {
case MD5:
this.algorithm(HMAC_MD5);
break;
case SHA1:
this.algorithm(HMAC_SHA1);