HashedMessageSchema
digeststringrequired
Example: 
sha256:abcdef1234567890algorithmstringrequired
Example: 
SHA-256HashedMessageSchema
{
  "digest": "sha256:abcdef1234567890",
  "algorithm": "SHA-256"
}
sha256:abcdef1234567890SHA-256{
  "digest": "sha256:abcdef1234567890",
  "algorithm": "SHA-256"
}