Addition to alphadin.bst that enables overriding of labels by the key attribute of BibTeX entries.

alphadin.bst

FUNCTION {key.label}
{ key #20 text.prefix$ } %% Length of 20 chars should be sufficient

FUNCTION {calc.label}
{ type$ "book" =
  type$ "booklet" =
  type$ "inbook" =
  or or
    'author.editor.key.label
    { type$ "proceedings" =
        'editor.key.organization.label
        { type$ "manual" =
            'author.key.organization.label
            'author.key.label
          if$
        }
      if$
    }
  if$
  duplicate$
  year field.or.null purify$ #-1 #2 substring$
  *
  'label :=
  key empty$ 'label 'key.label if$ 'label := %% Override automatically generated label with key, if it exists
  year field.or.null purify$ #-1 #4 substring$
  *
  sortify 'sort.label :=
}